INTRODUCTION

A riveted steel bridge located in Switzerland was built in 1897 and is composed of an arch of 48m span and approach viaducts. Columns support girders approximately every 10m over a total bridge length of 79.1m. The girders carry a single normal gauge railway open track (sleepers are directly fixed on the steel structure) for bi-directional passenger trains (Fig. 1).

Figure 1 The railway bridge with the scaffolding for installation of monitoring.

The superstructure consists of two girders built-up as double T girders from plates and L-shaped elements riveted together. The girder-to-girder connection is a butt joint formed of L-angles over the web height only, while the flanges are discontinuous. The structural and fatigue safety of the bridge was initially evaluated by "re-calculation" using the Swiss standards SIA 269 for existing structures. While sufficient structural safety at ULS resistance was found, the fatigue safety was evaluated to be insufficient. Consequently, intervention was recommended.

It is well known that fatigue safety assessment of existing bridges based on "re-calculation" using current code provisions are over-conservative, usually resulting in calculated insufficient fatigue safety triggering, sometimes, invasive interventions. This unsatisfactory situation is a theoretical, pseudoscientific "problem on paper" and does not reflect the real performance of the existing bridge.

Subsequently, it was decided to conduct a monitoring campaign in order to measure effective fatigue stresses in fatigue relevant details. This paper reports on the results.

MONITORING SET-UP

The aim of monitoring was to measure the stress variation at specific locations of the girders and to estimate the structural response under the train loading action. The first span from the abutment was se-Fatigue safety verification of a steel railway bridge using short term monitoring data

M. Nesterova

Laboratoire Expérimentation et modélisation pour le génie civil et urbain (EMGCU), The French institute of science and technology for transport, development and networks (Ifsttar), 77420, Champs-sur-Marne, France ABSTRACT: The case study of the fatigue safety examination of the 120 years old steel riveted bridge carrying a single railway track on two main girders is presented. The overall assessment according to the Swiss Standard SIA 269 for existing structures indicated sufficient resistance at Ultimate Limit State but not at Fatigue Limit State, and the replacement of girders was recommended. To challenge this, the detailed examination was performed using data obtained from short term monitoring by the system installed on the main girders of one span over a period of four weeks. Fatigue stress histograms were constructed, and it was shown that measured stress ranges are smaller than the fatigue endurance limit, indicating a theoretically infinite fatigue life. No structural intervention is thus necessary. This case study shows that a simple short term monitoring is very useful for the fatigue examination of bridges allowing for reducing or avoiding (costly) interventions on structures.

lected for the monitoring since the expected bending moments were highest, and for the sake of accessibility.

Both girders were instrumented using electrical strain gauges. Two cross-sections were instrumented with three strain gauges each (Fig. 2). Cross section 1 was located at mid-span of the girder, while Cross-section 2 was -as close to support as possible but outside of the joint area.

Strains were measured with a frequency of 300 Hz, and the measurement duration was 17 s per train. During the 4 weeks of monitoring, the strain histories of about 2'200 trains were recorded.

Figure 2 The scheme of monitoring. Dimensions in mm.

MEASURED ACTION EFFECTS

Data treatment

From the measured signals, the effects of train traffic were extracted by using the signal from the unloaded structure as zero value. In the present case, strain amplitudes due to temperature variation were not considered because of the short measurement dura-tion of each train passage. Also, they do not contribute to fatigue damage (Treacy, 2014).

Nature of traffic on the bridge

The entire set of recorded signals due to train passages, transformed into stress values using a modulus of elasticity of 210GPa, is presented in Figure 3 where the maximum value for each train is marked. Counting the peaks of each recorded strain history allowed determining the number of axles per train and thus the train type. The identified train types are given in Figure 5 showing the distribution of the rolling stock operating as follows:  4 cars, i.e. four module trains, further referred to as A-type  4+4 (4+3) cars, i.e. train composed of two fourmodule or three-and four-module A-type trains  Locomotive + 5 cars, i.e. train composed of the locomotive and 5 cars  Locomotive, i.e. locomotive without cars  Long train, i.e. train that could not be classified to any of above, probably with more passenger cars than 5.

When the histogram of extremes per train is plotted with distinction between train types (Fig. 5), the clear difference can be found between the Type A trains and the ones hauled by a locomotive. This is because of the much higher weight of the power car.

Figure 5 Histogram with division into train types. The border between two types of trains is marked with dashed line.

Figure 4 Stresses obtained from strains registered by gauge 1F during passage of train composed of the locomotive (pushing) and 5 cars.

Verification of monitoring duration

To verify whether the monitoring duration of 4 weeks was long enough to obtain reliable results, evaluation using an Extreme Value Theory (EVT) was conducted.

Given that a clear border exists between light multiple unit A-type trains (with recorded stresses below 27.5 MPa) and trains with locomotives (with stresses higher than 27.5 MPa), the two data sets were treated separately.

The threshold for tail fitting was chosen using Mean Residual Life plot. It was set to 21.5 MPa for first group and 32.5 MPa for the second one.

It was found that the return levels for the return period were close to the measured values (Fig. 6). This was expected, as the railway traffic is highly consistent and repetitive. Also, there was no isolated extreme event as can often be observed for road bridges (Treacy, 2014). This confirms also that the monitoring campaign was sufficiently long

Dynamic amplification

The dynamic amplification effects are largely overestimated in existing codes (Ludescher, 2003). For the investigated span (10.4m) the amplification factor according to European Standards is equal to 1.30, understood as an increase in vertical forces of 30%.

The amplification of loads due to dynamic effects of moving trains depends not only on the length of the span, but also on the velocity and weights of the trains. When comparing the recorded strain histories of same types of trains travelling at different times (thus possibly with different velocities), similar structural responses were found. Furthermore, the peak stresses due to passages of the subsequent axles of the same train were similar (Fig. 4).

Consequently, no amplification due to dynamic interaction between the moving trains and the bridge structure was found, despite the fact that the railway track is opened. The continuous rails of good rolling quality may explain this favourable result.

The above leads to the conclusion that the dynamic amplification effects are negligible and, as such, are included in the monitoring results. No further consideration of dynamic effects is needed.

Structural response

During the "re-calculation", it was assumed that each span acts as a simply supported beam and the girder-to-girder joint is a hinge.

The measurements revealed compressive strains at Gauge 2F (bottom of the beam, Fig. 2), indicating that a hogging moment exists near the supports. Figure 7 shows exemplary strain profiles over the height of the sections due to a random train passage. The measured strains are indicated with dots and the linear strain distribution is extrapolated over the entire height. A hogging moment for the section closer to the support is evident.

This means that the girder system acts similar to a continuous beam system. Consequently, the degree of fixity of connection was investigated Since the joint between two adjacent girders has some fixity, the loading on each span produces responses in the other. To compare the measured stresses with the results of structural analysis, the direction of train passage had to be considered. Passages of the trains coming from the abutment on the bridge were selected. Stresses were identified at the exact instant when the first boogie of the train was above the mid-span, providing the maximum stress there. Next, the ratio between stresses at the bottom of the girder were compared in the two monitored sections (gauges 1F and 2F). This ratio is depending mostly on the degree of fixity of the connection, and in average was equal to R=-0.25. The ratio is negative because the moment is changing from sagging to hogging.

Beam model

One girder of the monitored span was modelled by means of the ROBOT® Structural Analysis software using beam elements. At one end, a pinned support was modelled, and at the other end a vertical support and rotating spring. The rotating spring was simulating the fixity due to the girder-to-girder connection.

Because the stress variation due to train passage was measured, only the train loading was modelled. The first boogie of the Type A train was used, since this is the most common train on this line. Then, the rotating spring was tuned such as to obtain the same response as the measured one. Stiffness from 0, i.e. pinned support, up to infinity, i.e. clamped or full fixity, was used. The determined variation of stress ratio depending on spring stiffness is given in Table 1 with the best fit value in bold. The physical meaning of the numbers in terms of structural response is analyzed below.

Modelling of the girder-to-girder connection

The girder-to-girder connection was modelled using the commercial FEM package Idea StatiCa® connection module. All plates and elements were modelled with shell elements. The transfer of forces due to contact was enabled and the rivets were modelled as pre-tensioned bolts. The sectional forces found from the beam model were applied, i.e. M = 59 kNm and V = 53 kN.

In opened-deck railway bridges, continuous rails contribute to the structural behaviour (Herwig, 2008). To model this contribution, the slip and stiffness of sleepers and connectors need to be known. As no precise information was available, this contribution was estimated by modelling the rail being attached with C-shaped steel profiles to the girder, as shown in Figure 8. The results are presented in Table 2. In the model, only one rail to girder connection was used for each span, which is significantly increasing the stiffness. When using stiffer connectors or a higher number of those, like in the structure, the stiffness found from the beam model could be easily obtained. Such modelling was however not performed since no information on the connector's stiffness was available. Still, the model of connection allowed for the verification of the beam model's results.

Findings from the stiffness modelling

The partial fixity of the girder was proven, and thus the assumption taken during the "re-calculation" was not correct. The distribution of moments along the girders shows significantly smaller bending moments at mid-span than the initially "re-calculated" ones. Table 3 gives the comparison of bending moment distributions along the girder with different degrees of fixity. The following cases are considered:  Discontinuous, i.e. no connection with adjacent span, simply supported bridge  Monitored bridge, i.e. with same degree of fixity as in the bridge, stiffness from model found above  3 point continuous, i.e. multispan beam with point load in the middle  4 point continuous, i.e. multispan beam with two point loads spaced at 1/3 span  Fixed, i.e beam clamped over the support.

The loading due to Type A train's first boogie was used, and positive moments are sagging.

The results indicate that the fixity is partial, and the static scheme of the girder is between the two cases: simply supported and continuous beam. Therefore, the bending moment at mid-span is 16% smaller for the real static scheme comparing to the simply supported beam.

FATIGUE SAFETY OF THE BRIDGE

Methodology

According to the more than 30 years old approach in the domain of fatigue safety, several levels of verification are performed with the objective to verify sufficient fatigue safety and to avoid construction interventions.

Level 1 verification with respect to the fatigue limit, is the simplest and most difficult verification. If Level 1 verification fails, Level 2 has to be performed.

Level 2 is more complex as it includes the determination of an equivalent fatigue stress (considering fatigue stress spectra) that is compared to the fatigue strength (fatigue detail category).

Level 3 verification includes explicit fatigue damage accumulation using Palmgren-Miner Rule.

Level 4 verification is based on Linear Elastic Fracture Mechanics to calculate fatigue crack propagation due to fatigue stresses and comprises explicit consideration of inspection methods (to detect fatigue cracks) and their intervals.

Construction interventions like strengthening or replacement of fatigue critical elements are only conducted if the fatigue verification at the highest Level is not fulfilled. Consequently, if the fatigue safety verification at a lower level is fulfilled, no higher level verification is needed.

This methodology is prescribed in the Swiss Standards SIA 269 for Existing Structures and was applied in the present case.

Fatigue safety verification on Level 1

On Level 1, the fatigue action effect is described by the maximum fatigue stress range that is compared with the Constant Amplitude Fatigue Limit (CAFL) describing the fatigue resistance.

Fatigue action effects:

Using the measured stresses histories, histograms were produced using the Rainflow counting method. The histogram for the bottom of the girder at midspan (gauge 1F), showing the highest stress values, is presented in Figure 10.

The cumulative histograms after each week of measurements remained consistent, thus indicating that one week of monitoring would have been sufficient to obtain reliable results from the present regular passenger train traffic. The first bin, from 0 to 5 MPa, contains mostly measurement noise and was disregarded.

Since the monitored span was the longest of the entire bridge and the first span, the highest stress variations could be expected.

Because the girder does not act as a simply supported beam, the maximum moment is not located at the mid-span. From the beam model it could be deduced that the maximum stress ranges were about 5% higher than the measured ones at mid-span, so this increase has to be taken into account.

For the determination of fatigue relevant stresses in riveted members, the net section stress outside the riveted detail must be considered (i.e., no "hot spot" stress must be determined !). The gauges were thus intentionally not aligned with rivets in order to measure uniform gross section stresses. For the fatigue safety verification, the measured stresses are increased by 10% to account for net section stresses. However, the change of stress from gross to net section is not immediate, so this increase is quite conservative.

The standard SIA 269 allows for disregarding fatigue actions applied historically before year 1940 as historic train loads were smaller. The owner assured that cargo trains that can lead to stresses higher than measured are not operated on the line. However, the isolated event of a heavy train is not relevant in terms of fatigue loading.

The induced maximum fatigue stress range is Δσmax = 42.5 MPa × 1.05 × 1.10 = 49 MPa.

Fatigue resistance:

The constant amplitude fatigue limit (CAFL) is used in the present case. According to SIA 269/3 the detail category is 80MPa for riveted girders. As the girder can be inspected, the partial factor γMf,act =1.0; leading to the CAFL: ΔσD,80 = 58 MPa.

Fatigue safety verification:

Thus, the highest fatigue stress range in the girder is below the CAFL (Fig. 9) and no further verification is needed. The fatigue safety is verified and no intervention is justified.

Comment regarding the connection:

The girder-to-girder connection was shown to act as a semi-rigid connection. Consequently, stresses due to the train loading are transferred through the joint formed by the plate connecting the transversal truss to the girder (marked in Figure 8 with an oval), the vertical angle profiles forming the butt-joint and the continuous rail. Refined structural analysis indicated rather high fatigue stresses locally. However, local fatigue damage leading to failure of the joint is acceptable as it would only lead to a change in the static system to the (initially assumed) isostatic system. Such a change should be detected by inspection. Previous inspections did not reveal any indication of a fatigue damage in these details. In addition, it is planned to add a lamella to realize a continuous upper flange that will effectively strengthen the girderto-girder connection. 1. The monitoring allowed to determine real structural behaviour and realistic fatigue relevant stresses. It also eliminated the need for application of codified load models which are not appropriate for realistic fatigue safety verification.

2. In addition, uncertainty in structural behaviour could be reduced and refined numerical structural models could be calibrated to account for real structural behaviour. Monitoring thus allows to gain more precise and realistic information than "recalculation".

3. The utilized simple monitoring set-up turned out to be relatively easy to install and robust, leading to reliable readings.

4. Overall, examination by means of data from monitoring is economic since sufficient fatigue safety could be proven, and thus no intervention is needed, while conventional "assessment" by "recalculation" recommended strengthening.

Figure 3

 3 Figure 3 Stresses as obtained from all recorded trains during the monitoring. The marks show the maximum value per train.

Figure 6

 6 Figure 6 Return levels plots and goodness of fit for two sets of trains (27.5 MPa threshold).

Figure 7

 7 Figure 7 Strain distribution in cross-section due to train passage. Values measured by gauges are marked.

Figure 8

 8 Figure 8 FEM of the connection with the transversal truss connecting plater marked.

Figure 9 S

 9 Figure 9 S-N curve from SIA 269 for riveted details with stress range in girder.

Figure 10

 10 Figure 10 Stress variation histogram, 28 days of monitoring, gauge 1F.

  . Sawicki & E. Brühwiler Laboratory of Maintenance and Safety of Structures (MCS), École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland

B

Table 1 .

 1 Stress ratio depending on spring stiffness. ___________________________________________________

	Spring stiffness kNm/deg MNm/rad ___________________________________________________ Stress ratio -
	0 1800 2200 2500 Infinity	0 103 126 143 Infinity	0.29 -0.18 -0.25 -0.30 -2.11

Table 2 .

 2 Stiffness of modelled joint.

	MNm/rad ___________________________________________________ MNm/rad
	No rail With cont. rail ___________________________________________________ 38.4 41.5 67.2 87.1

___________________________________________________ Connection

Sj,ini (initial stiffness) Sjs (secant stiffness)

Table 3 .

 3 Moment distribution for different static schemes.

	___________________________________________________
	Case ___________________________________________________ Moment Moment Moment mid-span over support ratio kNm kNm -
	Discontinuous Monitored bridge 156 185 3 point continuous 169 4 point continuous 118 Fixed 114 ___________________________________________________ 0 0 -59 -0.38 -156 -0.92 -138 -1.17 -143 -1.25

  Herwig, A. 2008. Reinforced concrete bridges under increased railway traffic loads. Doctoral thesis. École Polytechnique Fédérale de Lausanne Ludescher, H. 2003. Berücksichtigung von dynamischen Verkehrslasten beim Tragsicherheitsnachweis von Strassenbrücken (in German). Doctoral thesis. École Polytechnique Fédérale de Lausanne Treacy, M.A. 2014. The use of monitored data in the verification of structural and fatigue safety of existing post-tensioned concrete highway bridges. Doctoral thesis. École Polytechnique Fédérale de Lausanne 7 ACKNOWLEDGEMENT This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 676139.


Chloé Eyssartier
email: chloe.eyssartier@cerema.fr

Marc Lanfranchi

Isabelle Ragot-Court

Lane splitting experiment: comparative analysis of how this is accepted by motorcyclists and car drivers

Keywords:

Lane splitting is a common riding practice although forbidden by the traffic rules in France. Since February 1st, 2016, a secure shape of traffic, respectful of certain rules is allowed on motorways and urban expressways in several French departments. The objective here is to present the results concerning the acceptability of this secure form of lane splitting for motorcyclists and car drivers. 908 car drivers and motorcyclists, representative samples of the French population (in terms of sex, age and socio-professional category) were interviewed. 751 lived in the experimental area and 157, in the control area where lane splitting is not allowed. The results show that the car drivers and the motorcyclists evaluate positively the experiment, the attitude of the experiment is even more positive for the motorcyclists. But, the car drivers have some reservations about the difficulty to understand where lane splitting is allowed. The results are discussed. As we will be replicating this research in 2017 and 2018, in order to study changes in how the experiment is accepted in the long term, at the end we will have some helpful elements, to decide if LS could be allowed in France.

Introduction

Although mobility using powered two-wheelers (PTW) accounts for only a small percentage of mobility for all modes of transport combined -2.5% in terms of kilometres travelled - [START_REF] Onisr | La sécurité routière en France. Bilan de l'année 2011. La documentation française[END_REF], it is greatly overrepresented in highly urbanized areas (Commissariat General for Sustainable Development, 2013). Lane splitting (LS), which consists of powered two-or three-wheelers moving between stationary or slowly moving queues of vehicles, or riding at slower speeds in dense and congested traffic, and more generally all types of overtaking between lanes, is in fact most often the consequence of an increase in the number of motorcyclists in increasingly congested traffic. These practices allow motorcyclists to take advantage of a section of unused road that allows them to pass between the lanes of other vehicles when stationary or moving slowly [START_REF] Sperley | Motorcycle lane-sharing[END_REF]. Untill 2016 , although common practiced by motorcyclists, LS was not authorized by the highway code throughout France. The Conseil National de la Sécurité Routière (National Concil of Road Safety) that brings together all the main actors in road safety adopted in 2013, a measure to experiment this practice. In this context, since 1 February 2016, LS by powered two-or three-wheelers, less than one meter wide, is being tested over a period of four years in the 11 departments. In these departments, a secure form of cross-line traffic complying with certain rules is allowed on motorways and motorway-like roads. The road users were informed about the experiment by spot radio, flyers or on the web site of the Délégation à la Sécurité et à la Circulation Routières (French delegation for road safety and traffic) .

In order to have a complete picture of the effects produced by authorizing LS in experimental areas, the Délégation à la Sécurité et à la Circulation Routières (French delegation for road safety and traffic) commissioned Cerema to study the behaviour of motorcyclists and car drivers (section 1), and to examine the acceptance of this new measure (section 2). The purpose of this paper is to present only this second part of the study for the first year of the experiment. Our objective is to study the acceptability of the experiment by the motorcyclists, those LS is a common practice, and by the car drivers that have to deal with this practice. The results could help to decide if the LS could be authorized by the highway code throughout France.

2-Theoretical background

From a global point of view, the rare accident analyses, recent or older, at national or international level [START_REF] Maids | In-Depth Investigations of Accidents Involving Powered Two Wheelers Version 2.0[END_REF], Clarke, et al. 2004[START_REF] Hurt | Motorcycle accident cause factors andidentification of countermeasures[END_REF], referring to this specific practice, conclude it has little impact on the occurrence of accidents ranging from less than 0.5% to 5% depending on the geographical area concerned. Not surprisingly, [START_REF] Crundall | Car drivers' attitudes towards motorcyclists: A survey[END_REF] found that these accidents occur more often on weekdays and at peak times (8 am and 5 pm). In France, traffic accident analysis bulletin (bulletins d'analyse d'accident corporel de la circulation -BAAC) data for the year 2010 reveals an accident rate involving motorcyclists "between two lanes" of traffic averaging 4%. Moreover, this specific accident rate is concentrated in Ile-de-France (Paris region) with a rate of 89.1% in 2010 and more particularly on the Paris ring road, with nearly one accident out of three (31.4%) [START_REF] Roy | L'accidentalité des motocyclistes en circulation entre deux files[END_REF]. However, specific work in France and more locally situated suggests that the issue related to PTW lane splitting is probably underestimated. The reason for this is that the manoeuvre identified in the BAAC as close to lane splitting is limited to the item "between 2 lanes". Specifically, these are situations where motorcyclists are moving at a moderate speed while vcar drivers are stationary or almost so. This results in deducing low accident severity, given the generally low speeds. The BAAC indication also does not take into account lane-changing accidents caused by motorcyclists moving to a position between lanes A detailed reading of the records for the year 2007 [START_REF] Clabaux | Contribution écrite au groupe de travail "Circulation interfiles / équipements de protection individuelle" de l'observatoire interministériel de sécurité routière[END_REF] shows that lane splitting accidents on the nonconcessionary motorway network of the Marseille urban area probably amounted to 7 cases, whereas according to manoeuvres identified only from the BAAC, it is noted that the police identified among these 7 cases only 2 for which the motorcyclists' "main manoeuvre before the accident" was "lane splitting".

The literature does not report information against lane splitting, but only in favour of it. However, we have no idea of the objective reality of the benefits put forward [START_REF] Sperley | Motorcycle lane-sharing[END_REF]. Lane splitting, and more generally all types of overtaking between lanes, is said to have environmental benefits by reducing traffic congestion [START_REF] Wigan | Motorcycles as a Full Mode of Transportation[END_REF], greenhouse gas emissions and damage to roads, infrastructure and cars. It is said of the specific practice of lane splitting that it might potentially reduce certain types of accident involving motorcyclists such as rear or front impacts in vehicle queues in the event of a sudden slowdown in traffic. But, driving in a narrow space can make accidents happen by simple lateral contacts with vehicles. Here too, available data on the question, for example on the Paris ring road, show no convincing effect [START_REF] Guyot | Circulation inter-files des deux-roues motorisés[END_REF]. The observation made by CETE Méditerranée (2012) in the south-east of France regarding lane splitting by certain motorcyclists (a minority) at a speed lower than that of vehicles in the left-hand lane could provide a basis for a strategy to prevent this risk of sudden slowdowns in queues during congested periods. As for the main perceived advantages of lane splitting by motorcyclists themselves, these are a reduction of journey time and reliability of travel time [START_REF] Hurt | Motorcycle accident cause factors andidentification of countermeasures[END_REF]Burge et al. 2007), by keeping vehicles moving. But for the car drivers, if motorcyclists lane splitting is a common practice for motorcycslits, it should be better to make a secure form of cross line trafic complying with certain rules (Autofil, Ragot-Court et al. , 2014).

Presentation of the experiment

The rules governing LS in the experimental zone are presented in the box below (Table 1):

Aim

The aim of this work is to learn how motorcyclists and car drivers understand, judge, conform to, or appropriate the rules of lane splitting. We made the hypothesis that motorcyclists have a more positive attitude on the experiment that the car drivers. We base this hypothesis on the idea that for the motorcyclists, LS is a common practice, while car drivers have to deal with it.

In the départements mentioned above, lane splitting is allowed...  on roads with several traffic lanes in the same direction  when traffic flowing in the opposite direction is separated by a central reservation  when motoryclists are travelling between the two leftmost lanes of the carriageway  when traffic is dense and it is running in uninterrupted lines on all lanes  when the maximum authorized speed is greater than or equal to 70 km/h Lane splitting is prohibited ...  for motorcyclists more than 1m wide  when the space between the lines of vehicles is insufficient  when roadworks are being carried out on at least one of the lanes  when weather conditions are unfavourable (snow, ice or strong wind)

Motorcyclists when lane splitting ...  must not exceed 50 km/h  must indicate when entering and exiting lanes  must not overtake another motorcyclists engaged in lane splitting Motorists must ...  leave sufficient space to facilitate lane splitting by motorcyclists  check their rear-view mirror and check blind spots before changing lanes  indicate before changing lane  avoid sudden manoeuvres

Method

Population examined

The scope of study on the acceptability of lane splitting covers: two distinct areas: the experimental zone, which includes all the departments subjected to the experiment, and the control area (one department ) not subjected to the experiment the 2 main populations concerned by lane splitting:  Dual-mode drivers defined as motorcyclists   Single-mode drivers defined as car drivers 

Method

After a pre-test phase with 61 respondents, the final questionnaire to study LS was distributed by a survey institute TNS Sofres, from June 16 to June 29, 2016 to 908 respondents distributed equally among the 12 departments (11 in the experimental area and 1 in the control area). The data collected in this way were weighted in order to obtain representative samples of the French population (in terms of sex, age and socio-professional category). The data from the questionnaires were processed using SPSS software. ANOVA and χ² were used for statistical analysis.

Questionnaire

In addition to socio-demographic information (age, gender, vehicle type), the questionnaire was divided into several separate sections to examine acceptance of the experiment as fully as possible.

However, here we will present only the main results dealing with  knowledge of the experiment: the experiment was presented in a few lines. Respondents were then asked whether they had any knowledge of it  the various dimensions composing the acceptability of the experiment were presented to the respondents who had to evaluate each according to whether they judged it to be more or less relevant on a 4-point scale: 1 perfectly relevant, 2; fairly relevant; 3 fairly irrelevant; 4 not at all relevant  the acceptability of the experiment was then evaluated by 8 items. 6 of them are about the understanding of the instructions, the dangerousness of the LS in link with its authorization or its , the ban, the ease of compliance with instructions and the utility of the experiment. Respondents had to score each of the 8 items on the scale 4-point scale: 1 perfectly agree, 2; fairly agree; 3 fairly disagree; 4 perfectly disagree.

 the practice of driving: the impact of the experiment on practices: whether LS had had an impact on how they drive both on and off urban expressways. More precisely, it was asked if they changed or not their practice since the beginning of the experiment.

Results

Population

In the experimental area, 379 LV and 372 motorcyclists were interviewed.

Relevance of the dimensions making up the measure

Whatever the types of road users or the area of living (experimental or control), the users evaluate the relevance of the measures positively. The means are between 1, 23 and 1,88. In other words, the respondents evaluate the measure as fairly relevant or perfectly relevant. About the measures about the speed limit, the means are between 2,02 and 2,32, in other words the respondents evaluate this item as fairly relevant or fairly irrelevant.

In fact, on a positive backdrop evaluation, the fact of whether or not they reside in the experimental area does not seem to have an impact on the acceptability of the experiment. On the other hand, it is essentially the type of user that seems to affect the relevance of the measure.

Motorcyclists evaluate the relevance of the following measures more positively compared to car divers in each of the experimental and control conditions (Table 3):  LS is allowed on multi-lane roads going in the same direction  LS is allowed when traffic flowing in opposite directions is separated by a central reservation,  LS is allowed when motorcyclists are travelling between the 2 leftmost lanes of the carriageway  LS is allowed when traffic is dense and is running in uninterrupted lines in all lanes (experimental condition  motorists must leave sufficient space to facilitate lane splitting by motorcyclists (experimental condition  motorists must avoid sudden manoeuvres However, some differences are found only with respect to one or the other condition, experimental or control . So for the experimental condition, motorcyclists find that it is better for LS to be allowed only when the speed is limited to 70 km / h while car drivers are more supportive of the idea that LS should be prohibited when there are roadworks on at least one lane .

For the control condition, motorcyclists are more favourable to the following items than car drivers:  Motorcyclists must indicate when entering or exiting lanes  Motorists must check their rear-view mirror and check blind spots before changing lanes  Motorists must indicate before changing lanes

4. Attitude to the experiment

First, regarding the set-up for the experiment, in terms of ease of application, dangerousness and utility of the measure, motorcyclists and car drivers have a positive (or a very positive) attitude : no respondent choose the " irrelevant" point of the scale. But we can note some differences, motorcyclists differ from car drivers independently of their area of residence (Table 4). motorcyclists consider that:

 the instructions are clear  it is easy to observe the instructions  it is useful  LS should be allowed everywhere However, the understanding of the areas where the LS is allowed seem difficult for the two types of road users, in keeping with the idea that « the experiment tends to make motorcyclists engage in lane splitting even where it is prohibited ». Futhermore, motorcyclists and car drivers have different answers on the more negative items about the LS and the experiment. So the motorcyclists consider that « Lane splitting is not dangerous per se: it should be allowed everywhere » and the car drivers do not agree with this item As a corollary, even having a mixed advice, the car drivers agree this the idea that « Lane splitting is dangerous per se, so it should remain prohibited » against the opinion of the motorcyclists. The car drivers are more worried about some perverse effects of the experiment tends to make motorcyclists engage in lane splitting even where it is prohibited, but only in the experimental area . The motorcyclists do not have a very different attitude on this item, which is coherent with the difficulty understanding in which areas lane splitting is allowed

Modification of behaviour

Most of the users declare not having modified their behaviour since the beginning of the experiment. However car drivers users in the experimental group were more likely to report that they changed their off-motorway and urban expressway behaviour than those in the control condition (χ2 = 4.65; p = 0.03). On the other hand, this result cannot be found for car drivers on motorways and urban expressways, in other words in areas where lane splitting is allowed (χ2=0.96 ns).

Opposite result are observed with motorcyclists. For motorcyclists, more people report having modified their behaviour in areas where experimentation is permitted than motorcyclists in the control area (χ2 ² = 4.74, p = 0.03). There were no differences off motorways and urban expressways between the two conditions for this population of users ( χ² = 2.025) (table 5).

Tableau 5: Number of people report having modified their behaviour since the beginning of the experiment

Conclusion

The results show that it is more the type of user, motorcyclists vs car drivers, which has an impact on the acceptability of the LS experiment than whether the respondents live in the experimental zone or the control zone. The knowledge of the experiment varies from one area to an other with about 2/3 of the users that are already informed in the experimental area and only half of them in the control area. It should indeed be noted that motorcyclists are more likely to have been aware of the experiment than car drivers, regardless of where they live.

When one looks at the relevance of the different measures that govern lane splitting, all users judge them positively but motorcyclists consider them to be more relevant overall than car drivers, regardless of where they live.

In other words, the experiment is judged positively and even more positively for the motorcyclists, probably because they already had this practice, lane splitting, before the experiment. This interpretation is based on the items that were more positively evaluated by the motorcyclists than by the car drivers in the control area (i.e. motorcyclists drivers must indicate when entering and exiting lanes / Motorists must check their rear-view mirror and check blind spots before changing lanes / Motorists must indicate before changing lane) . We will note a drawback that seems share by the two types of users, the understanding of the line in which areas lane splitting is allowed. This drawback could be explained by the fear expressed by the car drivers that the line splitting could tend to make motorcyclists engage in lane splitting even where it is prohibited. Maybe in the same logic, we can observe that more car drivers declared having modified their behaviour off-highway and urban expressed ways in the experimental area. For them, LS is a dangerous behaviour and many of them think that it should be forbidden.

About changing behaviours since the beginning of the experiment, first, most of the users declare not having changed their behaviours since the beginning of the experiment. However, if more car drivers than motorcyclists declare not having changed their behaviours on the type of road where the LS is allowed, it is perhaps because they think that their behaviours were already adapted to this practice that is not new . The other explanation could be that they feel less concerned and/or they think that they do not have to change their behaviour to conform a measure that is perceived as in favor to motorcyclists.

The main limitation of this work is that we do not interrogate the road users before the implementation of the experiment (acceptability). We could not compare the acceptability of the experiment with its acceptance. But as we will be replicating this research in 2017 and 2018, in order to study changes in how the experiment is accepted in the long term, at the end we will be able to know if LS could be allowed in France.

Table 1 :

 1 Rules governing lane splitting

Table 2 :

 2 Motorcyclists represent 82.5% (N = 296) of motorcyclists and female motorcyclists represent 17,5% (N=76) of motorcyclists. Car drivers represent 55,3% (N=214) of car drivers and female car drivers represent 44,7% (N=165). The mean age of car drivers is 49.98 years old (SD=15,09) and those of motorcyclists is 42.69 years old (SD=12,62). Concerning driving experiment of motocycle, the mean is 2.51 years (SD=1,09). Most of the motorcyclists ride a moto (65,5% N=298) and 34,5% a scooter. In the control area, 82 users are car drivers and 75 motorcyclists. Male motorcyclists represent 79,8% (N=71) of motorcyclists and female motorcyclists represent 11,2 % (N=4) of motorcyclists. Male car drivers represent 38,7% (N=25) of car drivers and female car drivers represent 61,3% (N=57). The mean age of the respondents is quite the same as those of the experimental area 43.10 years (SD=14,99) for motorcyclists and 45.49years (SD=14,62) for car drivers. Concerning driving experiment of a motorcyclist, the mean is 2.68 years (SD=1.11).More than half of the users reported having had knowledge of the experiment, except for the car drivers in the control group with 42% of informed users. For each of the studied population, the road users in the experimental areas are better informed about the experiment than car drivers in the control area[car drivers ; χ²=10.672 p=0.001 ; motorcyclists, χ²=4.068 p=0.044]. However, motorcyclists were better informed about the experiment than car drivers (experimental area :χ²=18.80 p=0.0001 ; control area :χ²=9.682 p=0.002) (table 2) with, in keeping with the previous data, a person rate having knowledge of the experiment higher for motorcyclists (75,7 vs. 65,2% ) (table2). Knowledge of the experiment

	Most of the motorcyclists drive a moto (71,1% N=64) and 28,9% (N=26) a scooter.
	6.2. Knowledge of the experiment:
	Experimental group	Control Group
	PTW	LV	PTW	LV
	75,7% (N=271 )	60,7% (N=224)	65,2% (N=58)	41,9% (N=39)

Table 3 :

 3 Evaluation of the measures governing LS

		Experimental Group	Control Group
		Motorcyc lists (M)	Car drivers( M)	Test and significance	Motorcyc lists(M)	Car drivers (M)	Test and significance
	LS is allowed on roads with several traffic lanes going in the same direction	1.68	1.95	F(1 ;724)=42.51; p=0.0001)	1.69	1.92	F(1 ;179)=3.98; p=0.048
	LS is allowed when traffic flowing in the opposite direction is separated by a central reservation	1.55	1.91	F(1 ;724)=21.99; p=0.0001	1.72	2.07	F(1 ;179)=3.98; p=0.005
	LS is allowed when PTWs are travelling between the two leftmost lanes of the carriageway	1.74	2.08	F(1 ;724)=36.38; p=0.0001	1.68	1.95	F(1 ;179)=36.38; p=0.003
	LS is allowed when traffic is dense and is running in uninterrupted lines in all lanes	1.64	1.97	F(1 ;724)=33.06; p=0.0001	1.74	2.08	F(1 ;179)=5.66; p=0.0001
	LS is allowed when the maximum authorized speed is greater than or equal to 70 km/h	2.02	2.31	F(1 ;724)=18.64; p=0.0001	2.32	2.25	Non-significant result
	Lane splitting is prohibited for motorcyclists more than one metre wide	1.72	1.7	Non-significant result	1.62	1.76	Non-significant result
	LS is prohibited when the space between the lines of vehicles is insufficient	1.61	1.62	Non-significant result	1.56	1.65	Non-significant result
	LS is prohibited when roadworks are being carried out on at least one of the motorcyclists lanes	1.85	1.65	F(1 ;724)=9.17; p=0.003)	1.75	1.76	Non-significant result
	LS is prohibited when weather conditions are unfavourable (snow, ice or strong wind)	1.73	1.64	Non-significant result	1.65	1.74	Non-significant result
	Motorcyclists must not exceed 50 km/h	1.85	1.9	Non-significant result	1.88	1.81	Non-significant result
	Motorcyclists must indicate when entering and exiting lanes	1.48	1.44	Non-significant result	1.32	1.6	F(1 ;179)=8.99; p=0.003)
	PTW drivers must not overtake another motorcyclist engaged in lane splitting	1.56	1.51	Non-significant result	1.46	1.53	Non-significant result
	Motorists must leave sufficient space to facilitate lane splitting by motorcyclists	1.52	1.85	F(1 ;724)=20.85; p=0.0001	1.57	1.95	F(1 ;179)=13.68; p=0.0001
	Motorists must check their rear-view mirror and check blind spots before changing lanes	1.33	1.39	Non-significant result	1.23	1.54	F(1 ;179)=13.678; p=0.0001)
	Motorists must indicate before changing lane 1.31	1.35	Non-significant result	1.24	1.43	F(1 ;179)=5.316; p=0.022
	Motorists must avoid sudden manoeuvres	1.3	1.85	F(1 ;724)=42.513; p=0.0001	1.29	1.64	F(1 ;179)=14.941; p=0.0001

Table 4 :

 4 Attitudes to the LS experiment

			Experimental Area		Control Area
		Motorcycl ists	Car drivers	Test and significance	Motorcyclis ts	LV	Test and significance
	The instructions are clear	1.8	2.18	F(1 ;724)=14.863; p=0.0001)	1.84	2.1	F(1 ;179)=5.13; p=0.025)
	It is easy to respect the instructions of the experiment	1.83	2	F(1 ;724)=9.606; p=0.002)	1.69	2.02	(F(1 ;179)=10.10; p=0.002)
	You have difficulty understanding in which areas lane splitting is allowed	2.44	2.43	Non-significant result	2.33	2.27	Non-significant result
	This experiment is useful in order to assess whether or not lane splitting is dangerous	1.86	2.07	F(1 ;724)=12.601; p=0.0001)	1.69	2.02	F(1 ;179)=5.175; p=0.024)
	Lane splitting is not dangerous per se: it should be allowed everywhere	2.21	2.78	F(1 ;724)=76.294; p=0.0001)	2.13	2.74	F(1 ;179)=26.054; p=0.0001)
	Lane splitting is dangerous per se, so it should remain prohibited	2.83	2.27	F(1 ;724)=64.889; p=0.0001)	2.69	2.25	F(1 ;179)=9.677; p=0.002
	The experiment tends to make
	motorcyclists engage in lane splitting even where it is	2.27	2.06	(F(1 ;724)=10.12; p=0.002)	2	1.99	Non-significant result
	prohibited.
	This experiment is pointless
	because it will not influence the behaviour of those motorcyclists who already engage in lane	2.08	2	Non-significant result	1.94	1.93	Non-significant result
	splitting


De Nicolò
email: m.denicolo@poliba.it

ONTOLOGY-BASED MODEL FOR PRODUCTION-CONTROL SYSTEMS INTEROPERABILITY

Keywords: Enterprise interoperability, Information modelling, Production-control systems integration, Ontological model, IEC 62264, OWL

One of the emerging control problem in manufacturing systems is the -information interoperability (I 2 )‖ problem: information is required to be coherent and congruent with the specific use, particularly in interfacing manufacturing processes, at any stage of the product lifecycle management. Lack of comprehension, misunderstandings as well as redundant activities are typically signs of I 2 problems. Standardisation initiatives, in the frame of ISO and IEC (IEC 62264), try to answer these problems by specifying the information related to products, manufacturing resources and processes. These represent the most assessed corpus of knowledge for business to manufacturing (B2M) applications interoperability, available so far for studying and solving the I 2 issues. This paper tries to trace a path for studying the I 2 problems in production-control systems, by a formalisation procedure to build an ontology-based model, based on the IEC 62264 standard.

PROBLEM STATEMENT

Managing distributed and delocalised productions is one of the strongest issues to address in the present era of market globalisation. Information becomes even more a key issue to face the emerging complexity of managing disperse manufacturing processes.

One of the emerging control problems in manufacturing systems concerns -information interoperability (I2)‖ problems. The problem of managing heterogeneous information coming from different sources, in order to achieve a unique meaning is typically an interoperability problem.

Interoperability can be defined as the ability of two or more systems or components to exchange information and to use the information that has been exchanged (IEEE, 1990). In more general terms, interoperability can be defined as that intrinsic characteristic of a generic entity (organization, system, process, model, …) allowing its interaction with other entities -to a different extent of simplicity -to cooperate for achieving a common goal within a definite interval of time, while pursing its own specific goal. Heterogeneous manufacturing systems, either inside a single enterprise or between networked enterprises, need to share information and to cooperate in pursuing their scopes. This information may be stored, processed and communicated in different ways by different systems, according to the scopes for which these have been collected and they will be used. Each enterprise system, in fact, uses an information repository, which refers to a Reference Information Model (RIM). A RIM specifies the structure and embeds the semantics of the information treated, in relation to the scope of the application to which it is devoted [START_REF] Dassisti | Product-driven Enterprise Interoperability for Manufacturing Systems Integration‖[END_REF].

The -Babel tower effect‖ induced by the heterogeneity of applications and their specific scopes, of users and of domains may cause information understanding problems, leading systems to fail in collecting information from different and heterogeneous sources to effectively ensure their local objective.

In order to manage heterogeneous information, it is appropriate to develop models able to trace all relevant information related to the product lifecycle (design, manufacturing, sales, use and disposal). This information is, in fact, quite often scattered within organizations: it is a matter of the materials adopted, of the applications used to manage technical data (e.g: Product Data Management systems (PDM)), of the applications that manage business data (e.g.: Enterprise Resource Planning (ERP)) and, finally, of the applications that manage manufacturing data (e.g.: Manufacturing Execution Systems (MES)).

The information problem born because the information need to be coherent and congruent with the specific use, particularly in interfacing manufacturing processes, at any stage of the product lifecycle management. Coherence addresses completeness and validity of information, meaning that information sets should be complete and reliable enough for the scope of their use in the manufacturing processes, independently of the IT applications adopted to manage them. Congruence addresses the matter of pertinence of information, i.e. usefulness and temporal significance of information. These two are sensible aspects to consider before reasoning about I 2 problems.

Questions pertinent to information exchange and its support may complicate the I 2 problem: lack of comprehension, misunderstandings, as well as redundant activities are some examples of loss of efficiency influenced by information exchange tasks. In fact, a problem of misunderstanding when information is exchanged between enterprise applications can occur, due to different view points, for which they have been developed and, consequently, a risk of loss of information semantics may arise when exchanging between heterogeneous systems. This latter seems to be the most important issue addressed so far, particularly in the IT research domain, even though also the coherence and congruence problems before cited are important as well from a technological point of view.

In a word, I 2 problem is not only a matter of how information is managed, but also on what kind and meanings of information is needed at different stages of the manufacturing processes during product lifecycle.

Standardisation initiatives (ISO and IEC) witness this problem, trying to solve the emerging problems of merging heterogeneous information, scattered within organizations and their IT applications, by formalising the knowledge related to product and process technical data.

Standardisation initiatives, in the frame of ISO and IEC (IEC 62264), try to answer these problems by structuring the information related to products, manufacturing resources and processes, thus representing the most well assessed corpus of knowledge for business to manufacturing (B2M) applications interoperability available so far for addressing the I 2 issues. Furthermore, even though prescriptive, this approach represents a widely shared and consensual knowledge useful for addressing interoperability of manufacturing systems.

In this paper a path for studying the I 2 problems in production-control systems is traced, by proposing a formalisation approach to build an ontology-based model, centred on the IEC 62264 standard. The use of a formalised approach and of a information model is here sustained to be a valuable one to address interoperability issues, either inside a single enterprise or between cooperating networked enterprises. Addressing the heterogeneity of IT applications adopted to control different manufacturing processes is in fact a matter of finding a common ontological meaning. Test cases on the proposed ontology, using Protégé tool and inference engines are presented to demonstrate the feasibility of the approach for production-control systems interoperability.

IEC 62264 STANDARD AND B2MML

Information interoperability (I 2 ) asks for common shared approaches: in fact, interesting standardisation initiatives already exist, such as the IEC 62264 set of standards (IEC 62264, 2002) and the ISO 10303 technical specifications (ISO/TS 10303,2004). They try to solve the problem of managing heterogeneous information coming from different systems by formalising the knowledge related to products technical data. Both these standards are related to Product Data Management at the business and the manufacturing levels of enterprises (B2M). In this paragraph a short review will be done of these two standards. The IEC 62264 set of standards specify a set of reference models extending the ANSI/ISA S95 (ANSI/ISA, 2000) specifications, that defines an information exchange framework to facilitate the integration of business applications and manufacturing control applications, within an enterprise. It is composed by six different parts designed for defining the interfaces between enterprise activities and control activities. Among all its parts, part 1 describes the relevant functions within an enterprise and within the control domain of an enterprise, stating which objects are normally exchanged between these domains (Figure - The model shows the hierarchical levels at which decisions are made. The interface addressed in the standard is between Level 4 and Level 3 of the hierarchy model. This is generally the interface between plant production scheduling and operation management and plant floor coordination. Levels 2, 1, and 0 present the cell or line supervision functions, operations functions, and process control functions, not addressed by this standard. Level 0 indicates the process, usually the manufacturing or production process. Level 1 indicates manual sensing, sensors, and actuators used to monitor and manipulate the process. Level 2 indicates the control activities, either manual or automated, that keeps the process stable or under control. There are several different models for the functions at these levels based on the actual production strategy used. To take into account the various exchanged information, through the product representation, the standard defines a set of eight models that specifies all concepts for enterprise-control integration. Each model concerns a particular view of the integration problem. Those models show increasing detail level and are operational models or resource models The different models from IEC 62264 are linked together in a logical way in order to define a hierarchy of models ( Product Definition Model (Figure -4): the product definition model is information shared between production rules, bill of material, and bill of resources. A product definition contains a listing of the exchanged information about a product. The information is used in a set of product segments that are the values needed to quantify a segment for a specific product. A product segment identifies, references, or corresponds to a process segment. It is related to a specific product, while a process segment is product independent. The collection of product segments for a product gives the sequence and ordering of segments required to manufacture a product in sufficient detail for production planning and scheduling. The corresponding production rule presents the additional detail required for actual production.

Material Model: the material model defines the actual materials, material definitions, and information about classes of material definitions. Material information includes the inventory of raw, finished, and intermediate materials. Material classes are defined to organise materials. A Material definition is a means to describe goods with similar characteristics for purposes of scheduling and planning.

Equipment Model: the equipment model contains the information about specific equipment, the classes of equipment, equipment capability tests, and maintenance information associated with equipment.

Personnel Model: the personnel model contains the information about specific personnel, classes of personnel, and qualifications of personnel.

Process Segment Model: the process segment model contains process segments that list the classes of personnel, equipment, and material needed, and/or it may present specific resources, such as specific equipment needed. A process segment may list the quantity of the resource needed. A process segment

Production Capability

Product Definition

What must be defined to make a product

Process Segment

Segment Property

Resource Segment Capability

Process Specification

What can be done with the resources is related to a product segment that can occur during production, as presented in the product definition model.

Production Schedule Model: a request for production shall be listed as a production schedule. A production schedule shall be made up of one or more production requests. A request for production for a single product identified by a production rule shall be shown as a production request. A production request contains the information required by manufacturing to fulfil scheduled production. This may be a subset of the business production order information, or it may contain additional information not normally used by the business system. A production request may identify or reference the associated production rule. A production request shall contain at least one segment requirement, even if it spans all production of the product.

Production Capability Model: the production capability information is the collection of information about all resources for production for selected times. This is made up of information about equipment, material, personnel, and process segments. It describes the names, terms, statuses, and quantities of which the manufacturing control system has knowledge. The production capability information contains the vocabulary for capacity scheduling and maintenance information.

Production Performance Model: the performance of the requested manufacturing requests shall be listed as production performance. Production performance shall be a collection of production responses. The responses from manufacturing that are associated with a production request shall be used as production responses. There may be one or more production responses for a single production request if the production facility needs to split the production request into smaller elements of work. A production result may include the status of the request, such as the percentage complete, a finished status, or an aborted status.

Even if all models specified in the standard are important for trying to answer the I 2 problem of an enterprise, the paper will focus on analysing one of them: the material model (Figure -3).

The material model is a resource model that defines the actual materials, material definitions, and information about classes of material definitions. Material information includes the inventory of raw, finished, and intermediate materials. Material classes are defined to organise materials. A material definition is a means to describe goods with similar characteristics for purposes of scheduling and planning.

A material class is a means for defining sets of material definitions. A material class may be further characterised through zero or more material class properties. The material class properties usually define the nominal or standard values for the material. A material definition property does not have to match a material class property. A material lot uniquely identifies a specific amount of material, as defined by its Material Definition. It defines specific instances, where Material Lot Properties have specific values, regarding a particular Material Definition and its Material Definition Properties. Material lots and Material sublots may be used for traceability when they contain unique identification. A material lot may be stored as a separate identifiable quantity. Each separate identifiable quantity of the material is identified in a material sublot object. The semantics attached to these constructs realises a semantic interoperability between business applications (level 4) and manufacturing operations (level 3). Information described in IEC 62264 is collected into information categories. The categories of information provide the overview for the object model (Brandl 2001, IEC 62264-1 2002). Information required producing a product: this is ‗Product Definition Information' dealing with ‗how to make a product'. It answers the question of ‗What does it take to make a product?'. This may be a specific product, such as a specific model of a car, or may be a rate of production, such as a production rate of liquid gas, etc. Information on the capacity to produce a product: this is also called ‗Production Capacity Information'. It answers the question ‗What is available'? It defines what the production system is capable of doing: (1) to the level of detail required for planning and scheduling; (2) taking into account maintenance activities; and (3) taking into account committed and available capacity and capacity. Information about actual production of the product: also called ‗Production Information'. This is concerned with ‗what to make and results'. In other words, it answers the questions: ‗What should be used to make the product?', ‗When is it due?' or ‗When can it be made?' It also provides production follow-up information and answers the question ‗What was made?', i.e. what was actually used to make it, when it was made, how long it took, etc. Some information in each of these three areas is shared between the production control systems and the other business systems. These three information categories are used to define formal information models which are detailed sufficiently for actual enterprise-integration projects. In other words, each category of information is detailed further by one or several models. The eight object models developed in IEC/ISO 62264 aim at: (1) identifying categories of information; and (2) defining formal definitions of shared information. The term ‗formal' does not have a mathematical sense; instead, it is concerned with the set of necessary data attributes that contribute to better define the semantic of the information (Tursi et al, 2007).

FROM THE STANDARD TO THE ONTOLOGY

The IEC 62264 standardisation initiative tries to answer the I 2 problems by specifying the information related to products, manufacturing resources and processes, thus representing the most assessed corpus of knowledge for business to manufacturing (B2M) applications interoperability, available for studying and solving the I 2 issues.

This approach is rather prescriptive, but it represents a widely shared and consensual knowledge useful for addressing interoperability of manufacturing systems. In fact, the IEC models represent a common standardised knowledge built by expert of the domain.

The standard's models can be defined a sort of ontology. An ontology, in fact, provides formal definitions of basic concepts in a domain and the relationships among them in a usually logic-based language [START_REF] Gruninger | Ontology -applications and design‖[END_REF].

In order to overcome questions pertinent to information exchange and its support, such as loss of information, problems of misunderstanding as well as redundant activities, which may complicate the I 2 problem, it's necessary to define an ontology-based information model, to support information exchange between IT applications adopted to control different manufacturing processes and systems.

There have been, in many different sectors, some efforts examining the use of ontologies in supporting the semantic integration task (e.g. Gehre et el, 2005;[START_REF] Guo | Ontology-based product data integration‖[END_REF][START_REF] Katranuschkov | An ontology framework to access IFC model data‖[END_REF][START_REF] Lima | Interoperability among semantic resources in construction: is it feasible?‖[END_REF], Patil et al., 2005). Aware of the efforts demonstrating the integration of models using ontologies, the matter of the approach, discussed here, is to trace a path for studying the I 2 problems in production-control systems environment, by appropriately formalising an ontology-based model, based on the IEC 62264 standard. In this sense, standards efforts can be taken into account, in term of useful bases for the ontology of the domain. To the scope of the present paper, in order to develop the abstraction meaning of the concepts, based on the standard (which is more at a logical level), we have de-normalised and conceptualised its models and then represented them using the UML class diagram notation. This was done because UML is the most used and known language to model application structure behaviour.

THE ONTOLOGY IMPLEMENTATION AND ANALYSIS

This This scenario is composed of 2 ATL transformations: the core transformation UML2OWL takes as input a UML model and produces an ontology conforms to the OWL meta-model (OWL ontology + OWL Individuals from a UML Model + UML Instances). The second transformation is an XML extractor that produces an XML document conforms to the OWL/XML syntax, as defined by the W3C specification. The core transformation (UML2OWL) includes two distinct parts. The first part is dedicated to the mapping from UML model to ontology, i.e. UML classes are mapped into OWL classes, attributes into datatype property, associations into object property, etc.. The second part of the transformation deals with instances that are defined in the same class diagram as the UML model. Those instances are converted into OWL individuals (OWL term for instances). This method offers the possibility to manage UML instances and populate the ontology with corresponding knowledge.

The UML2OWL transformation can produce an OWL model in ecore format or an OWL document conform to the OWL/XML presentation syntax. To obtain this XML file, the tool implements an OWL/XML extractor that transforms a model conforms to the OWL metamodel into an OWL document. This makes it possible to use the obtained OWL files under ontology tools like Protégé, the one available under the UML eclipse project (eclipse.org/uml2).

OWL (Web Ontology language) is the most expressive language for representing and sharing ontologies over the Web. OWL is designed for use by applications that need to process the content of information instead of just presenting information. It facilitates greater machine interoperability of Web content than other description languages like XML, RDF and RDF-S by providing additional vocabulary along with a formal semantics. The OWL metamodel is implemented in by extending the RDFS metamodel. This ATL scenario makes possible the conversion of an arbitrary UML model into an OWL ontology, that is, provides a solution for bridging modeling tools based on UML or MOF and tools for the Semantic Web and ontology development. The complete scenario of this transformation is given in figure below.

CONCLUSIONS

The approach proposed to build an ontology-based model tries to face information interoperability problems by using two main concepts: formalisation (using appropriate knowledge management tools) and standardisation (using shared standards). The final result, which is in phase of completion, will be a model with a final aim to address interoperability issues either inside a single enterprise or between cooperating networked enterprises, as well as addressing heterogeneity of IT applications adopted to control different manufacturing processes. The paper serves to present the idea and trace the technical path to follow for the construction of the ontological model. Proof are not possible here because test cases of reasoning analysis on the proposed ontology, using Protégé tool and inference engines, need to be performed to demonstrate, in the next future, the efficacy and efficiency of the approach for production-control systems interoperability.

Figure 1 -

 1 Figure 1 -Functional hierarchy as defined in IEC 62264

  Figure -2). The production information presents what was made and what was used. Its elements correspond to information in production scheduling that listed what to make and what to use. The production scheduling elements correspond to information in the product definition that shows what is specified to make a product. The product definition elements correspond to information in the process segment descriptions that present what can be done with the production resources.

Figure 2 -

 2 Figure 2 -The IEC 62264 models hierarchy (IEC 62264, 2002)

Figure 3 -

 3 Figure 3 -The conceptualized IEC 62264 Material Model

  paragraph traced the engineered procedure used to transform the conceptualized IEC 62264 models into a ontology-based model useful to solve the I 2 problem in production-control systems. The tool considered for the UML-to-OWL transformation has been realized in the Eclipse platform (http://www.eclipse.org) by the SIDo Group from the L3I lab in La Rochelle. It is freely available from the Eclipse website at the following address: http://www.eclipse.org/m2m/atl/atlTransformations/. The work is an implementation of the Object Management Group (OMG) Ontology Definition Metamodel (ODM) specification using the Atlas Transformation Language (ATL). ODM offers a set of meta-models and mappings for bridging the meta-modelling world and the ontologies. The solution supports the UML (Unified Modeling Language) 2.0 meta-model and the OWL (Web Ontology Language) meta-model as defined in ODM. The ODM is a recently adopted standard from the OMG that supports ontology development and conceptual modeling in several standard representation languages. It provides a coherent framework for ontology creation based on MOF (Meta Object Facility) and UML. In this way it played a central role for bridging Model Driven Architecture based standards and Semantic Web technologies.

Figure 5 -

 5 Figure 5 -OWL overview

Figure 7 -

 7 Figure 7 -UML2OWL complete transformation scenario

Figure 6 -

 6 Figure 6 -The engineered system to build the ontological model in OWL

Automation Science and Engineering ;Vol. 2, 2005, pp 213-225. Terzi S. (2005)


Magnus Blomkvist
email: mblomkvist@audencia.com

Johannes Kortekangas

Hitesh Vyas

Credit Rating Levels and Acquisitions: The European Evidence

Keywords: JEL Classification: G30, G32, G34 Mergers and Acquisitions, Credit Ratings, Financial Constraints

This study examines the impact of credit rating levels on acquisitions in Europe. In line with a financial constraints explanation, we find that improving the credit rating level by one notch increases the acquisition likelihood by 1.87pp or 8.1% (from baseline estimates). As the rating level further increases, firms begin to forego acquisition opportunities resulting in an inverse U-shaped relation between credit rating levels and acquisitions. The pattern is consistent with that high rated firms manage their credit rating levels by mitigating acquisition-induced downgrades. Overall, our results imply that European managers give relevance to their credit rating and that higher ratings relaxes financial constraints facilitating acquisitions.

Introduction

We study the impact of credit rating levels on acquisitions in Europe. Acquisitions are mainly debt financed and leverage increasing [START_REF] Harford | Do firms have leverage targets? Evidence from acquisitions[END_REF], which ultimately leads to credit rating downgrades [START_REF] Aktas | Credit ratings and acquisitions[END_REF] 1 . Survey evidence by [START_REF] Graham | The theory and practice of corporate finance: evidence from the field[END_REF] points out that maintaining credit rating levels is the second most important criteria when determining capital structure. The manager's priority to maintain credit rating levels can thereby disincentivize acquisitions. Meanwhile, a higher credit rating is also linked to enhanced access to acquisition financing [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF][START_REF] Aktas | Credit ratings and acquisitions[END_REF] and may cause firms to conduct acquisitions, where the increased capital supply can even lead to potential overinvestment [START_REF] Harford | Bond market access and investment[END_REF]. Hence, the credit rating level offers several predictions on the firm's M&A activities.

The European setting offers a unique laboratory, traditionally Europe's banking sector is wellfunctioning (Van Lanschoot, 2008), meanwhile the bond markets relevance have been questioned (Von Beschwetz and Howels, 2016). As a result only 7.3% of the European public firms [START_REF] Blomkvist | Bond market access and acquisitions: empirical evidence from the European market[END_REF] have a credit rating compared to 28.1% in the U.S. [START_REF] Harford | Bond market access and investment[END_REF]. Furthermore, the European M&A markets differ substantially due to market fragmentation, varying levels of market development and legal standards [START_REF] Porta | Legal determinants of external finance[END_REF][START_REF] Martynova | The performance of the European market for corporate control: Evidence from the fifth takeover wave[END_REF]Drobetz and Momtaz, 2020). With this background, we contribute to the literature by studying how credit rating levels affect acquisitions in a European setting.

Recent studies analyze the interaction between credit ratings, capital supply and M&A activity on U.S. data. Bond market access measured by having a credit rating relaxes financial constraints [START_REF] Faulkender | Does the source of capital affect capital structure?[END_REF]. In line with a financial constraints explanation, [START_REF] Harford | Bond market access and investment[END_REF] find evidence that credit rated firms conduct more but have lower average returns to acquisitions relative to non-rated firms. However, as their study shows nonnegative CARs, which does not suggest that credit rated firms use their additional capital supply to overinvest. Not only having a credit rating impacts capital supply but also the credit rating level. [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF] report that firms with higher credit ratings settle transactions to a greater extent with cash. [START_REF] Aktas | Credit ratings and acquisitions[END_REF] find an inverse U-shaped relation between credit rating levels and acquisitions.

Our study extends the work of [START_REF] Aktas | Credit ratings and acquisitions[END_REF] and [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF] to a European setting. We test two competing hypotheses: the financial constraints and the managing for rating hypotheses. First, the financial constraints hypothesis postulates that debt market frictions lead to a potential underinvestment problem [START_REF] Stiglitz | Credit rationing in markets with imperfect competition[END_REF]. In the absence of frictions, firms conduct all NPV positive acquisitions. Meanwhile, financially constrained firms selectively invest in the highest NPV projects. This results in less acquisitions and greater announcement returns among financially constrained acquirers. Hence, rating levels should be positively related to the acquisition likelihood and the use of cash, but negatively related to the acquirer announcement returns. A related explanation to the financial constraints hypothesis, stems from that managers can deviate from their investors' objectives and use their additional capital supply to overinvest [START_REF] Jensen | Agency costs of free cash flow, corporate finance, and takeovers[END_REF][START_REF] Harford | Corporate cash reserves and acquisitions[END_REF]. Overinvestment suggests a greater acquisition likelihood and below zero CARs. Second, the managing for rating hypothesis [START_REF] Aktas | Credit ratings and acquisitions[END_REF], postulates that managers are concerned about downgrades and thereby more conservative in their acquisition activities, particularly at higher rating levels. Consequently, firms are reluctant to pursue cash settled acquisitions due to the potential acquisition-related downgrades. Hence, the managing for rating hypothesis predicts that the credit rating level is negatively related to the acquisition likelihood and using cash as acquisition currency.

To study this in a European setting slightly alters the interpretation of the two main hypotheses. The financial constraints hypothesis is only indirectly related to bond market financing. Because a higher rating level also correlates with characteristics associated with greater access to bank credit. Instead, studying the curve-linear relationship between credit ratings and acquisitions shows if managers perceive bond ratings as irrelevant. Conveying if firms at the higher rating levels forego acquisition opportunities to mitigate downgrades. Such a behavior results in an inverse U-shaped relation between credit rating levels and acquisitions.

Using a sample of 2,959 European firm-years between 1.1.2000-31.12.2017, we find a positive relation between credit rating levels and acquisitions. We attribute this finding to lower financial constraints and enhanced capability of highly rated firms to access financing. As the rating level further increases firms begin to forego acquisition opportunities resulting in an inverse U-shaped relation between credit rating levels and acquisitions. The pattern is consistent with that high rated firms manage their credit rating levels by mitigating acquisitioninduced downgrades. When further taking into account the method of payment, we find a stronger curve linear relation for cash payments relative to mixed and stock payment, to avoid potential downgrade risk.

We perform several tests to analyze the robustness of our results. First, we test for the severity of potential omitted variable biases using the Oster (2019) coefficient stability test. The Oster (2019) test analyzes if observable characteristics are at least as important as unobservable characteristics in determining the acquisition likelihood. Second, we explore a channel of reverse causation, that firms increase their credit rating by freeing up debt capacity to conduct acquisitions (Morelec and Zhdanov, 2008;[START_REF] Uysal | Deviation from the target capital structure and acquisition choices[END_REF]. Our results hold up after including lagged upgrade and downgrades in our main analysis. Third, we test for potential biases due to our variable construct, where we transform credit ratings into a continuous variable. After creating indicators for credit rating categories, our curve linearity results remain intact. We further rule out an alternative explanation, that our results are due to overinvestment by high rated firms with greater access to cheap debt capital.

The study is structured as follows. Chapter 2 presents the data and method. In chapter 3 we present the results and chapter 4 concludes the study.

Data and Method

We retrieve our sample from the Eikon database covering 1.1.2000-31.12.2017. The sample includes all listed firms from the EU-11 countries that adopted the euro in 1999 and non-euro countries: Denmark, Sweden, UK, Norway and Switzerland. In accordance with previous studies (e.g., [START_REF] Blomkvist | Bond market access and acquisitions: empirical evidence from the European market[END_REF][START_REF] Harford | Bond market access and investment[END_REF], we exclude financial firms and regulated utilities, and firm-years with sales below €1 million. After our initial filtering and further excluding firm-years with missing data, our sample consists of 28,697 firm-year observations. Out of these firm-year observations, we exclude all firms without a S&P longterm issuer credit rating, and end up with a final sample of 2,959 credit rated firm-years. As in [START_REF] Aktas | Credit ratings and acquisitions[END_REF] we construct our main independent variable (Rating Level), by the S&P rating, numerically assigning AAA (C) as 20 (1).

In accordance with Harford and Usyal (2014), our M&A sample includes majority bids with deal value greater than 1% of the total assets of the acquiring firm. We drop firms with missing deal values. After the initial screening, we end with 547 acquiring firm-years. We construct our main dependent variable, the acquisition likelihood (ACQ) as an indicator that equals one if the firm conducts at least one acquisition during the given year. We include ln(Sales), Cash/Assets, Market Leverage, 12-Month Return, Market-to-Book, EBITDA/Assets, Herfindahl, M&A Liquidity as control variables as in [START_REF] Harford | Bond market access and investment[END_REF]. We winsorize all accounting variables at the 99 th percentile. All variables are defined in Table A1.

We conduct four set of tests. The first set replicates [START_REF] Aktas | Credit ratings and acquisitions[END_REF] and aims to explain the acquisition likelihood with the credit rating level. We estimate the following model:

(1) 𝐴𝐶𝑄 𝑖,𝑡 = 𝛽 ′ 𝑅𝑎𝑡𝑖𝑛𝑔 𝐿𝑒𝑣𝑒𝑙 𝑖,𝑡-1 + 𝜸 ′ 𝑿 𝒊,𝒕-𝟏 + 𝜀 𝑖,𝑡 , where X is a matrix of control variables. In our main specifications we further include the squared rating level (Rating Level^2) to test for curve linearity. The second set of tests, include only completed transactions, to study the rating levels effect on the CAR and the propensity to pay with 100% cash as in [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF]. In these tests, the sample size reduces to 467 observations due to the availability of payment method and return data. We further conduct two robustness tests. First, to analyze if past rating level changes cause firms to conduct acquisitions. Second, we split the rating level variable into indicators building on rating categories.

Table 1: Descriptive statistics

This table reports descriptive statistics. ACQ is an indicator variable taking the value of one if the firm conducts an acquisition during year t. Rating level is the firm's credit rating classified as AAA (20) to C (1). Market leverage is (Total debt)/(Total Assets -Book equity + Market Capitalization). M/B is (Total Assets -Book equity + Market Capitalization)/Total Assets. Size is the natural logarithm of sales in 2018 euros. Cash/Assets is cash holdings scaled by total assets. 12-Month Return is the firm's lagged stock return. Herfindahl is based on sales in the 3digit industry. M&A Liquidity is (Industry deal value/Industry total assets) measured on 3-digit industry level. All independent variables are measured at t-1. Our sample is shown in Table 1. What is striking is the high acquisition likelihood among European rated firms (23%) compared to 18% in [START_REF] Aktas | Credit ratings and acquisitions[END_REF]. In general, our descriptive statistics suggest that the credit rated European firm is different from U.S. firms. This is likely due to the higher boundaries for European firms to self-select into having a credit rating.

Variable

Results

We test two competing hypotheses offering different predictions on the relation between credit rating levels and acquisitions: the financial constraints and the managing for rating hypothesis. We report our main findings in Table 2. In columns (1) and ( 2), we study the cross-sectional relation between rating levels and acquisitions. 2 In non-reported marginal effects we observe that increasing the rating by one notch from the average rating leads to an increase in the acquisition likelihood by 1.87pp (8.1% from the mean value), suggesting that a higher credit rating relaxes financial constraints. In column (2), we include the squared rating level in the model and report a curve linear effect. The squared term is statistically different from zero (p<0.05). By including year fixed effects we capture differences in the macro environment and also changes in rating standards [START_REF] Alp | Structural shifts in credit rating standards[END_REF]. In columns ( 3) and ( 4) we control for crossindustry heterogeneity by including industry fixed effects. Our results remain intact, a positive relation between the credit rating level and acquisitions and a negative relation between the squared credit rating level and acquisitions. When studying the within-firm relation in column (5), we instead find no relation between credit rating levels and acquisitions.3 One possible explanation is that due to the low time-series variation in rating levels, the firm fixed-effects almost fully absorbs the rating level variation and makes it difficult to draw any inference (see, e.g. [START_REF] Bae | Creditor rights, enforcement, and bank loans[END_REF]). An alternative is to use random firm-level effects that take into account both cross-sectional and time-series variation. By including random effects in column (6), the relation becomes positive and gradually decreases over the rating levels as in [START_REF] Aktas | Credit ratings and acquisitions[END_REF]. In order to take into account country heterogeneity stemming from market fragmentation, we have in unreported tests added country fixed effects to Models (1) and ( 2) of Table 2. Our findings remain intact after the inclusion of country fixed effects. In general, our findings are in line with a financial constraints explanation. However, in specifications (2), ( 4) and ( 6) we further report that managers refrain from acquisitions at the highest rating levels. In Table 3 columns (1) and ( 2), we study the effect of credit rating levels on the 21-day cumulative abnormal return (CAR). We find no direct relation between the rating level and acquirer announcement returns. However, when we include the squared rating level in specification two, which indicates that mid rated firms have a higher CAR. Our results do not provide any conclusive evidence of overinvestment, since there is no direct linear relation between credit rating level and acquisitions. The overinvestment hypothesis postulates that higher rated firms should have lower announcement returns compared to low rated firms. To further test the financial constraints and managing for rating hypotheses we study the choice of payment method conditional on that an acquisition takes place. We argue that both the financial constraints hypothesis and managing for rating hypothesis are more sensitive to using cash as currency in the transaction. Cash payments are usually financed by debt issuance, bank loans or internal funds and thereby net-leverage increasing [START_REF] Martynova | What determines the financing decision in corporate takeovers: Cost of capital, agency problems, or the means of payment?[END_REF].

In columns ( 3) and ( 4), we test the relation between credit rating levels and the payment method. In line with our expectations, we find a positive but decreasing relation between rating levels and 100% cash payment relative to mixed and stock payment. We address potential endogeneity problems as follow. First, we conduct the Oster (2019) coefficient stability test on our main specifications [Columns (3) and (4) of Table 3]. The Oster methodology creates an omitted variable bias adjusted beta (lower bound for the coefficient estimates). A lower bound of beta that does not change sign indicates that the observables are at least equally important as the unobservable characteristics (δ=1) in determining the acquisition likelihood. In the Oster test we use the proposed 𝑅 𝑚𝑎𝑥 2 of 1.3*𝑅 2 as model inputs, where 𝑅 2 is the R-squared from the estimated models. After applying the Oster (2019) methodology for testing the coefficient stability both the Rating Level coefficient in Column (3) and Column (4) remain positive, suggesting that the omitted variable bias is not severe. Second, we explore potential reverse causality. Both Morelec and Zhdanov (2008) and [START_REF] Uysal | Deviation from the target capital structure and acquisition choices[END_REF] provide insight into how future acquisitions may cause changes in credit rating levels. They argue that firms free up debt capacity in order to have a greater possibility of winning a potential bidding contest. The potential de-leveraging is also likely to map into higher credit rating levels. Lower leverage ratios are correlated with higher rating levels (see, e.g, [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF]. To rule out this reverse causality channel, we include indicator variables for prior upgrades (downgrades) capturing changes in the credit rating level one and two years prior to the potential acquisition year. Our findings in Table 4 do not suggest that prior changes in credit rating levels drive our results. We also address concerns about multicollinearity, since the control variables correlates with the credit rating level. We perform a VIF test to ensure our results are not driven by bias stemming from collinearity of explanatory variables. In un-tabulated results, we find that the VIF in our main specification is above the recommended threshold of 10. Therefore, we exclude Size and obtain an acceptable VIF of 4.34 and re-estimate our results using this specification. The positive coefficient of Rating Level and negative coefficient of Rating Level^2 remain statistically different from zero.

The Rating Level variable is an ordinal variable transformed into a continuous variable. Since, increments in credit rating levels are not symmetric in terms of credit risk and cost of debt capital [START_REF] Jorion | Information effects of bond rating changes: The role of the rating prior to the announcement[END_REF][START_REF] May | The impact of bond rating changes on corporate bond prices: New evidence from the over-the-counter market[END_REF], we create indicators for rating categories and reestimate our main results in Table 5. In the first two columns we test the effect of having an investment grade rating on acquisitions. Our findings suggest that firms with an investment grade rating are more likely to conduct acquisitions relative firms with a speculative grade rating. In columns ( 3) and ( 4), we test for curve linearity, that firms at higher and lower rating levels refrain from conducting acquisitions. To test for this, we let AAA, B and C rated firms act as intercept and include indicators for AA, A, BBB and BB rated firms. Our results indicate that firms with a rating level in the middle of the spectrum have a greater acquisition likelihood. In unreported tests, we have further examined the effect of credit rating levels on other types of investments (CAPEX and Asset Growth). Our results do not suggest a similar pattern for other investments as for acquisitions. One possible explanation to this pattern is that firms with a credit rating are usually mature firms [START_REF] Blomkvist | Credit ratings and firm life-cycle[END_REF], and mature firms are more likely to grow through acquisitions instead of building new capacity.

Conclusions

We study the impact of credit rating levels on acquisitions in Europe. Europe offers a unique setting different from the U.S., due to market fragmentation and the lesser role of bond market financing. Our findings on the two hypotheses: the financial constraints and the managing for rating hypothesis lend support to both. In particular, the acquisition likelihood is positively related to the rating level. However, at higher rating levels firms refrain from conducting acquisitions which create a curve linear relation between credit rating levels and acquisitions. This relation is further strengthened when cash serves as payment currency in the transaction.

Our results suggest that that high rated firms take actions to maintain their higher rating levels. Due to the minor role of bond markets as debt financing source, our findings are less pronounced compared to U.S. studies (see, e,g., [START_REF] Karampatsas | Credit ratings and the choice of payment method in mergers and acquisitions[END_REF][START_REF] Aktas | Credit ratings and acquisitions[END_REF]. Nonetheless, our results highlight that managers are averse to downgrades and higher ratings are linked to enhanced access to acquisition financing.

Table 2 :

 2 Credit rating levels and acquisitions

	denotes

This table report Logit, OLS and Probit estimates using Acquisition likelihood (ACQ) as dependent variable. All variables defined as in Table

A1

. Singleton observations are dropped, this causes a lower number of observations in the firm fixed effects models. Clustered (Firm) robust t-values are reported in parentheses. ***, **,*

Table 3 :

 3 CAR and method of paymentThis table reports OLS and LOGIT estimates of the rating level effects on CAR and 100% cash payment. CAR is Horizontal takes the value of one if the acquirer and target have the same 3-digit industry code. Clustered (Firm) robust t-values are reported in parentheses. ***, **,* denotes 1%, 5%, 10% significance, respectively.

	(1)	(2)	(3)	(4)
	CAR -10/+10	CAR -10/+10	Cash 100%	Cash 100%

calculated using the market-adjusted model, i.e. the excess return over the MSCI Europe, -10/+10 day relative to the bid announcement. Cash100% is an indicator taking the value of one if the firm uses 100% cash as payment. Relative size is (deal value/acquirer total assets). Public Target takes the value of one if the target is publicly traded. Cross-Border takes the value of one if the acquirer and target originates from different countries.

Table 4 :

 4 Previous rating changes and acquisitionsThis table report Logit, estimates using Acquisition likelihood (ACQ) as dependent variable. All variables defined as in TableA1. Clustered (Firm) robust t-values are reported in parentheses. ***, **,* denotes 1%, 5%, 10% significance, respectively.

	(1)	(2)	(3)	(4)
	ACQ	ACQ	ACQ	ACQ

Table 5 :

 5 Rating categoriesThis table report Logit, estimates using Acquisition likelihood (ACQ) as dependent variable. Investment Grade is an indicator variable taking the value of one if the firm has a BBB-or above credit rating. AA, A, BBB and BB are credit rating category indicators. The control variables are identical to the ones in Table2. Clustered (Firm) robust t-values are reported in parentheses. ***, **,* denotes 1%, 5%, 10% significance, respectively.

		(1)	(2)	(3)	(4)
		ACQ	ACQ	ACQ	ACQ
	Investment Grade	0.5398***	0.4615***
		(2.993)	(2.603)
	AA			1.8569***	1.5165***
				(5.006)	(3.805)
	A			1.7610***	1.5760***
				(5.442)	(4.749)
	BBB			1.4936***	1.3051***
				(5.173)	(4.670)
	BB			1.1801***	1.0528***
				(3.921)	(3.493)
	Observations	2,959	2,959	2,959	2,959
	R-squared	0.0597	0.0837	0.0663	0.0886
	Controls	YES	YES	YES	YES
	Year Effects	YES	YES	YES	YES
	Industry Effects	NO	YES	NO	YES
	Firm Effects	NO	NO	NO	NO
	Model	LOGIT	LOGIT	LOGIT	LOGIT

We find a similar pattern in our sample (non-reported). Where the average acquiring firm lowers its credit rating by 0.43 notches within

years (t-value relative to non-acquiring firms is 2.7).

[START_REF] Pastor | Do funds make more when they trade more?[END_REF] show that using year fixed effects is similar to estimating a Fama and Macbeth cross-sectional regression with different weighting scheme, and that firm fixed effects mimics N time-series regressions.

We estimate the firm fixed effects models using a linear probability model (OLS) instead of Logit regressions due to the inclusion of a large number fixed effects, Logit and Probit are not consistent estimators in that case.[START_REF] Angrist | Mostly harmless econometrics: an empiricists companion[END_REF] show that using a linear probability model instead of Logit and Probit yields similar estimates.