Ariane ; Dupont-Kieffer

Merle

Nicolas

Hivert

QUETELARD, Bernard Laurent

Laurent Hivert

QUETELARD Bernard Laurent

Environment Energy Assessment of Trips: Lille Region

Keywords:

This paper deals with sustainable mobility in an urban context. We investigate the assessment of the impacts of the evolution of travel behaviour (travelled distance and modal choice) in terms of energy consumption and greenhouse gases (GHG) emissions at the local level. Indeed, today, the control of exhausts generated by the mobility within the urban areas is at the core of the environmental policies and the stabilisation of GHG emissions is one of the main goals of 'sustainable development'. To face this challenge in the transport sector, the national government and local authorities need a better understanding of the link between urban development choices, the operation of the different modes of transport systems, and residents and non residents' attitude, and mobility patterns at the local level.

For this purpose, INRETS defined a new approach enabling to estimate and relate the inventory of mobility-related energy consumption and pollutant emissions to the individual behaviours, as they are decribed in the local mobility surveys.

 2 is based on trips made by individual on a casual weekday within his regions of residence and provides spatialized energy consumption and GHG emissions assessment of it. It includes at the disaggregated level:

on the one hand, a "daily Transport-related energy Budget" (TEB), which gives the sum of energy consumption related to the daily mobility of each individual, -on the other hand, several "daily Pollutant Emissions Budgets" (PEB) accounting for the carbon dioxide and each of the regulated pollutants (carbon

The assessment method is applied to the case of Lille, the largest Metropolitan Urban Area of in the Northern part of France. We adopt a longitudinal perspective over the 1990s, based on the 1987[START_REF] Certu | Inventaire des émissions de gaz à effet de serre en France au titre de la convention cadre des nations unies sur les changements climatiques[END_REF]/2006 Household Travel Surveys, showing then the salient dynamic patterns. The paper is two-fold. On the one hand, we develop an analysis of the environmental balance of the residents of the area, computing daily energy and air pollutants budgets over two decades. We compute then EEBT for the Lille residents in a context of a slight fall of mobility. On the other hand, the original initial method is enriched in order to take into account all types of traffics (as to say residents and non-residents flows and freight flows within the Lille Region but also crossing the Region); this updated methodology is applied to provide a 2006 enlarged assessment.

Concerning the results in perspective, we point out that the decrease of energy consumption and CO2 emissions related to transport activities has a double impact both in change in travel behaviour but also in the renewal of the car fleet integrating new technological improvements (section 2). But the enlargement of the analysis balances these results. Indeed, we show that the reduction of EEBT for the residents is not compensating the huge growth of CO2 emissions due the important development over the two decades of the flows of non-residents and of freight external flows (section 3). This situation is the result of the overwhelming share of haulage and road passengers' traffics (with more longer distance trips, notably due to urban sprawl) also observed in other France and Europe metropolitan areas, but especially here in a strategic region being at the cross-road of the different business centres of Europe.

Environmental balance of the inhabitants of Lille Region: stabilisation of GHG emissions 21 Methodology

A. Environmental assessment of air pollution of the transport sector The Mobility Environmental Diagnosis (MED) aims to estimate the energy consumption (in goe or grams oil equivalent with one unique unit which is 1 liter of gasoline = 750 goe, 1 liter of diesel = 840 goe), and the emissions of Air Regulated Pollutants and Greenhouse Gases directly related to transportation and traffics.

> Greenhouse Gases (GHG):

Though the GHGs have no direct and local health impact, they contribute to the mid-and long-term climate change. The current and/or probable future consequences of Climate change are: modification of average earth surface temperatures and level of precipitations more or less important according to the regions, increasing frequency of extreme weather events (tempests, hurricanes, and heatwave), rise in the level of oceans, modification of landscapes, and reduction of biodiversity.

Carbon dioxide (CO2) accounts for 95 % of the GHG emissions by the transport sector. Our method of diagnosis, the MED, computes the contributions of transportation by a unique indicator, the CO2 equivalent (eqCO2), which «adds up» the contributions of the different GHGs by using an equivalence defined in terms of the century global warming potential of each atmospheric gas. For example, the emission of one ton of methane (CH4) contributes 23 times more than one ton of carbon dioxide to global warming. This rate is of 130 in the case of nitrogen protoxide (N2O), third and last GHG taken into consideration in this indicator.

> Local air pollutants:

These gases (when present in the air) contribute to the worsening of air quality at the scale of urban areas (downtowns, suburbs and peri-urban areas). Their harmfulness (in high concentrations) has been acknowledged for many years now (Several epidemiological studies dealing with the health effects of air pollution from automobiles): -carbon monoxide (CO), is a poison gas (suffocation) which, at high concentrations, settles in haemoglobin, and prevents the transport of oxygen by blood; -nitrogen oxids (NOX) are mainly composed of nitrogen monoxid (NO), which generates cyanosis and of nitrogen dioxid (NO2), which harms respiratory tracts and can generate severe poisoning in case of exposure to high concentrations; -hydrocarbons or volatile organic components (VOC)3 , very worrying from the health point of view, gather many pollutants as aldehides, benzene, toluene, etc. several of them being carcinogenic; -total particles hanging in the air (pm) group together very heterogeneous suspended substances (aerosols, smokes, ashes, pollen, smog…), without any consideration to their chemical composition and nature. As the particles emitted by diesel engines, the smallest particles can deeply penetrate into the respiratory system4 .

The latest results are used to establish dose-effect relationships, distinguishing: -The short term, following several days of minimal increases in daily levels of some of these pollutants. Are studied cardiopulmonary mortality, and acute episodes of bronchial asthma attacks, particularly along the known risk groups (infants and young children, elderly, cardiac or respiratory failure); -And the long-term effects of cumulative effects over a long period, observing the effects of increasing concentrations of annual averages, with the onset of cancers, including lung, and installation of chronic diseases such as bronchitis chronic.

Knowing the exposure of the population, the dose-effect relationships can calculate a number of cases of these diseases due to air pollution. Finally, epidemiological surveillance, in a large number of towns in France and Europe, allows to highlight the (short and long term) health effects of urban air pollution, for wihich around half (decreasing share) is due to road traffic. The risks are "low" at the individual level, but, considering the importance of exposed population size, the numbers of cases related to this pollution are finally significant. Moreover, CO, NOX and VOC chemically change with solar radiance and produce ozone and other dangerous substances (species) for health and environment. Despite significant decreases in CO and VOC emissions, the concentration of ozone in the atmosphere is regularly increasing. Ozone spreads on large geographical scales and contributes to greenhouse effect.

B. EEAT method to compute energy consumption and air pollution due mobility if residents

The quantities of CO2 emitted by the residents during their trips whithin their urban area are estimated by INRETS, according to our previously developed EEAT method (for this assessment and budgets method, see details in [START_REF] Gallez | Environment energy budget of trips (EEBT) : a new approach to assess the environmental impacts of urban mobility[END_REF], [START_REF] Quételard | Diagnostic Énergie-Environnement des Déplacements dans l'arrondissement de Lille[END_REF] and (Hivert, 2007)), using the emissions coefficients recommended at the European level in COPERT III methodology, MEET Project [START_REF] Inrets | Methodology for calculating transport emissions and energy consumption[END_REF].

The "Environment Energy Budget of Trips" is based on trips made by an individual on a casual weekday within his or her region of residence. It includes:

-on the one hand, a "Transport-related Energy Budget" (TEB), which is equivalent to the overall energy consumption resulting from his or her trips ;

-on the other hand, several "Pollutant Emissions Budgets" (PEB), accounting for carbon dioxide and each of the four regulated pollutants (carbon monoxide, hydrocarbons, nitrogen oxides and particulate matters) the total volume of pollutants emitted during those trips.

As opposed to more traditional methods aimed at drawing up an inventory of pollutant emissions from transport activity as observed on the networks, the approach related to the Environment Energy Budget of Trips is not intended to determine the overall pollutant emissions generated by traffic. Its purpose is rather to simulate the variations of energy and environmental impacts of the population mobility within a given urban area as a result of the global change in individual behaviour.

Applying this experimental method to three great French urban regions (Grenoble, Paris, Bordeaux and Lille for two consecutive mobility surveys, 1987 and 1998) led us to outline some conclusive results:

-First, at the disaggregated level, we have confirmed the influence of land use on individual mobility demand and, consequently, on its environmental impacts: for instance, higher densities go with lower Transport Energy-related Budget;

-Second, after answering the question "Who pollutes?", we have tried to answer the question "Where do we pollute ?", by drawing pollutant emissions maps at the local level. Those maps, obtained from trips assignment on the transport network, emphasize the respective weights of the different types of links in concentrating traffic and pollutant emissions with particular attention to the long distances generated form or to the farthest outlying suburbs.

Based on successive household mobility surveys (1987[START_REF] Certu | Inventaire des émissions de gaz à effet de serre en France au titre de la convention cadre des nations unies sur les changements climatiques[END_REF]and 2006 THS for Lille) describing the daily mobility on a working day, this method determines energy consumption and pollutant emissions (including CO2) at the disaggregated level of each trip (of each individual) described in the survey, with respect to trip length, speed and used modes. For the car trips, the vehicle technological characteristics (fuel type, age and cubic capacity) and cold starts are taken into account, while occupancy rates intervene in estimation for PT trips.

In the initial EEBT method, estimating of the fuel consumption and the pollutant emissions due to the trips within the urban region of residence relies on two distinct statistical sources and is based on the main following assumptions:

- and coll. 1990, 1991, 1992). For car driver trips, the unit rates of consumption and pollutant emissions are estimated from relatively complex equations, taking into account, besides the type of fuel, the age and power of the vehicle, the speed of the trip as well as the cold starts. For other motorized modes, unit rates do not depend on the average speed.

-And last, the hypothesis of nullity of energy consumption and pollutant emissions is retained for the passengers of the trips made by car, in the absence of information on the occupation rate of the vehicles. This hypothesis means that the totality of the fuel consumption and the pollutant emissions are allocated to the driver of the vehicle.

C. Data and Zoning

« PDU » zoning for the Lille Metropolitan Area

The Lille conurbation, with multipolar urban form, is the fourth of France.

The zoning for Lille has been elaborated for the "Urban Mobility Plan"6 . The territory is structured by: -two main city centres (only 4% of the total surface), Lille and Roubaix-Tourcoing, -two zones of suburbs around these poles (respectively 25% and 13% of the total surface for Lille and Roubaix-Tourcoing suburbs; 31% of the population for Lille suburb)

Environment Energy Assessment of Trips: Lille Region DUPONT-KIEFFER, Ariane; MERLE, Nicolas, HIVERT, Laurent, QUETELARD, Bernard 6 -and a peri-urban zone (55% of the surface for 17% of the population). These 5 PDU areas, also used for the presentation of our MED results, include the 57 zones of the THS (household survey).

The Mobility Environmental Diagnosis made for that current research covers the territory of the Lille urban community (LMCU for Lille Métropole Communauté urbaine, established in 1967), which corresponds to the urban transport perimeter of the Lille built-up area.

In 2006, the LMCU counts 85 districts for an area of 611.45 km 2 and a total population of 1 107 861 inhabitants. The main towns of this territory are:

-Lille : 226 014 inhabitants -Roubaix : 97 952 inhabitants -Tourcoing : 92 357 inhabitants -Villeneuve d'Ascq : 61 151 inhabitants Two urban poles structure this territory: the main one being Lille, and a secondary one, Armentières, with 24 836 inhabitants.

LMCU Household Travel Survey

As the surveys carried on in 1987 and in 1998, the 2006 survey was conducted according to the national methodology of the «travel households survey7 » defined by the CERTU (Centre d'Études sur les Réseaux, les Transports, l'Urbanisme et les constructions publiques) [START_REF] Certu | Inventaire des émissions de gaz à effet de serre en France au titre de la convention cadre des nations unies sur les changements climatiques[END_REF][START_REF] Certu | Inventaire des émissions de gaz à effet de serre en France au titre de la convention cadre des nations unies sur les changements climatiques[END_REF].

But, the 2006 edition referred to the « updated » THS methodology, as to say:

• Specially trained pollsters carry out Interviews at the home of the surveyed individuals;

• One or two persons over 5 years old, living in the place of residence, are interviewed (only one person if the size of the household is one or two persons, and two persons when the size of the household is over two persons), this latter aspect being the peculiar characteristic of the methodological updating of the THS.8 ;

• All the trips made the previous day by the interviewee are listed and detailed in all their characteristics.

Indeed, these characteristics include purpose at destination, modal choice9 , origin and destination zones, departure and arrival time. All modes are taken into account including walking.

This precise picture of daily mobility in the urban area, obtained with the last edition of the THS, has to be compared to the previous ones in order to catch mobility patterns (and behaviours) changes overtime.

For the 2006 edition, between January and June, 8 990 inhabitants were selected to be representative of the population of the 85 districts of LMCU and were interviewed at their home about their "yesterday" trips.

The selected households were stemmed from:

• A random draw, on 57 geographical zones shaping the Lille Urban Community, in the lists of place of residence (housing) established by the Tax Administration 10 ;

• A sample of 41 student households living in residence halls. All in all, 36 244 trips were registered (see below the descriptive scheme of the sampling).

No possible distinction between the "internal" households and the "non internal" households, as a consequence of the updated methodology

Results: the (internal) mobility of Lille Region inhabitants and its environmental impacts over two decades

The 2006 THS shows, for the first time since the 1970s, a mobility decrease in terms of number of trips, and a stabilization of road traffic in terms of travelled kilometers by the Lille Urban Community inhabitants. When carrying out the exercise of the "classical" EEAT estimation, we can note that this stabilization is translated in a decrease by 8 % up to 9 % of the energy consumption and GHG emissions as well as in a striking decrease of the emissions of the air local pollutants.

Less and less polluting trips, but their contribution remains high

The main part of the energy consumption and of the related emissions is the results of car use: the observed changes over the three succssive THS (1987, 1998 and 2006) follow from the one hand the technological improvements and from the other hand the evolutions observed in car use. The GHG emissions follow the same trend with a higher growth between 1987 and 1998 (+38 %), time period where the technological improvements of vehicle engines were mainly focused in reducing local air pollutants (NOx, VOC in particular), more than dealing with CO2 concern.

Apart from the particles, the emissions of local air pollutants have strongly decreased, on a continuous trend, for 20 years since 1987: -50 % for NOx, -80 % for CO and VOC.

• The special case of particles

The specificity of particles emissions is the following: in the 1987-1998 period, these emissions were multiplied by 4, as the result of an intense «dieselization » of the car fleet (from 10 % up to 34 % of the whole fleet at the National level and from 7 % up to 33 % in the Lille region case). But in the next period, between 1998 and 2006, they decreased by 25 %, thanks to particles filter, while the share of diesel car on the total fleet was still increasing. Indeed, from 1/15 in 1987, this share was of 1/3 in 1998 and almost 1/2 in 2006.

Observing the new vehicle market in Europe, we notice that diesel seems no longer to be a 'French exception' since the early 2000s: the share of Diesel among new vehicles market becomes higher in Austria, Belgium and Luxembourg than in France, and the average share is growing continuously in Europe since 1998. The level and nature of the polluting emissions related to individual trips are dependent of the modal choices, and of the travelled distances in each (consecutive) mode. The kilometers travelled by car are the most determining, whereas trips practices are tightly related to age, level of income, lifecycle and residence locations.

• A/ Important disparities among modes in terms of contributions to emissions

Not surprisingly among all the modes, individual road vehicles represent the higher fossil energy consumer and the main supplier of GHG and local air pollutants. In Lille Urban Community, more than half of the trips are done by car (54 % of the total number of trips, in summing drivers and passengers of car), but they also account for 74 % of the travelled distances. Thus, car is identified, in an even much larger proportion, as the main transport mode for energy consumption (92%) and for exhausts with 93 % of the GHG emissions, and even 95 % carbon monoxide emissions.

Other modes

Car

Acknowledging the overwhelming weight of road transport is particularly meaningful when compared to the impact of 'soft' (or active) modes as cycling and walking. Their modal share is 35 % of the total number of trips, they account for 8 % of the travelled distances and, of course, they are completely free of GHG and local air pollutants. Other modes

2-wheel vehicles

Motorized two-wheel vehicles are a very important source of VOC (volatile organic components) emissions. In spite of their low modal share (only 0,7 % of the total number of trips), bikes, scooters and other mopeds contribute to 8 % of VOC emissions. Finally, one can underline that one kilometer travelled by motorized two-wheel vehicles produces 8 times more VOC than one kilometer travelled by car.

• B/ Labour force, main contributor to energy consumption and polluting emissions

Most of the GHG emissions are produced by members of the labour force; and between these active emitters, men are far ahead women (+ 30 %). This huge difference is explained by the fact that men travel longer distances than women and that they more often use car as transport mode than women. People without work emit three times less GHG than workers. This situation can be explained by the significant contribution of home-to-work commuting trips to the total mobility, and even more to the total emissions, wehter GHG or local air pollutions.

GHG emissions (g) according to individuals' status

• C/ Some trip purposes appear predominant > Pollution is mainly generated by trips related to work

Trips related to professional occupation account for :

-20 % of the total number of trips done by inhabitants, -but 34 % of travelled distances -and 40 % of the emissions of GHG, NOx and particles. Indeed, such trips are longer, and partly for this reason, very more often done by car (80 % against 54 % in average, considering modal share in number of trips).

Share of public transports in the number of trips, distance and GHG emissions

Other purposes

Studies

Work

> Trips for education purposes contribute less to polluting emissions… Education as destination purpose (home-to-school trips) represents 14 % of the total number of trips, but only 4 % of GHG emissions, due to shorter travelled distances and massive use of modes like public transport, walking and cycling.

>… While accompaniment trips are an important (noticeable) source of pollution Indeed, accompaniment is often made by car: 15 % of trips, 12 % of travelled distances, and 17 % of GHG emissions. Most of accompaniment trips have school as destination purpose.

We can notice that, in perspective between both last THS in 1998 and 2006, the share of this trip purpose seems to have decrease, while the global traffic stabilized.

• D/ The hourly distribution of pollution is directly related to hourly distributin of road traffic

The temporal distribution of emissions strictly follows up the one of trips made by car. Defining this distribution allows to identify the periods of strong emission peaks, preceding periods of high concentrations of nocive local gases in the air. This analysis by hourly schedule confirms the impact of work related trips on traffic peaks and congestion and thereby on the peaks of emissions in the morning and early evening (especially for NOx, main indicator for local pollutants emissions for cars, but one can observe the same trends for other local pollutants).

Hourly distribution of NOx emissions

0% 2% 4% 6% 8% 10% 12% 0 h 2 h 4 h 6 h 8 h 1 0 h 1 2 h 1 4 h 1 6 h 1 8 h 2 0 h 2 2 h 2 4 h
Home-to-work and/or home-to-school distances (and finally schools, works and residents locations) and the accessibility to transport infrastructures strongly matter in order to reduce GHG emissions. Not only density is a silver bullet to sustainable mobility but also diversity of activities over the territory (mixed uses or functional mixity of the spaces), the design of transport infrastructures, the distance to transit and the destination accessibility.

• E/ The environmental impact of trips is closely related to the individual position in the life cycle

> Education is a key determinant of mobility patterns and therefore of the level of energy consumption and generated emissions. The relationship between the level of education and the GHG emissions is almost linear: the more graduated the individuals are, the more they use their car and the more they contribute to greenhouse effect and to worsening of air quality. The level of education is certainly related to the age but this correlation has been observed for each age group.

GHG emissions (g) according to the level of education

Studies

> Income is also a main determinant of travel patterns and then of their environmental impact. Indeed, the daily average quantity of GHG emited by individual has been computed by classes of household income by consumption unit11 and the result is crystal clear: Members of households with monthly income are less than 1 000 € per consumption unit, have an average level of GHG emissions of 1700 g by individual. This figure is doubled for households belonging to the second class (monthly income between 2 000 € and 3 000 €).

The increase in GHG emissions between the individuals of this second class of income and the individuals belonging to the last class (i.e. with a household monthly income over 3 000 € per consumption unit) is less strong, but a step is still identified. This disaggregation of GHG emissions by class of income confirms the results obtained by disaggregating by education level. There is no surprise in there, since these two variables are obviously highly correlated: the higher the level of education is, the higher the level of income is. Moreover, Individuals with the highest incomes also have most of the time the highest activity rates and therefore their working activity generates many more trips than the average and these individuals favor faster transport modes and cars in particular. Despite the fact their high level of education allows them a better access to the knowledge and a better awareness on environmental issues, the travel behaviour of the most educated and wealthy individuals and households in the population remains the most energy consuming and pollution generating.

GHG emissions (g) according to the level of household's income

• F/ Urban sprawl generates longer travelled distances, and then pollution

Rsidential location, density of settlement, and diversity of activities in the same places (housing, work places, shopping, leisure …) are all together key factors in explaining distortions in the level of emissions related to trips of the inhabitants of a geographical zone.

The results of Lille are no exception, and confirm different effects already underlined in our previous local case studies (comparing disaggregated estimations), as well as in Newman and Kenworthys' more aggregated works about "cities and automobile dependence".

Population density (inhabitants/ha) and individual GHG emissions (g) according to households' location of residence.

Mapping based on the 57 zones of the Lille Urban Community, zoning used for the 2006 LMCU THS.

The number of inhabitants by hectare and the individual emissions of GHG of inhabitants are directly and strongly correlated: the less the territory is densely populated, the higher is the level of individual emissions, and vice versa, as previous EEBT as shown in the past.

> The difficulty to provide an efficient PT supply in outer suburbs and periurban areas Density and diversity of activities by zone favor proximity trips and thereby cycling and walking, but also promote the development of quite efficient and attractive for all public transit. [START_REF] Newman | Cities and automobile dependence : an international sourcebook[END_REF], 1999) On the opposite, population living in the fringes of the urban area is induced to travel longer distances to reach jobs (often in the city-centre(s)), activities equipments and services, provided by the Urban Community, because all these amenities are generally not close to their home. The cluster of traffic flows related to urban sprawl does not allow the implementation of efficient collective public transit: this explains the huge amount of kilometers travelled by cars by the residents of these zones and the important emissions related to these flows.

> The level of emissions is getting higher as the places of residence are far from downtowns.

Urban sprawl is inducing an overwhelming use of car as transport mode but more a growing car dependency. The contrasted results for GHG and local air pollutants emissions according to the places of residence, wether they are located in downtowns, in inner suburbs or in the farthest fringes of the urban area are especially speaking for themselves (even in the multipolar specific case of Lille).

The inhabitants of the zones far away from city centres are those who generate the most polluting trips: when traveling, a inhabitant of periurban areas emits twice as much GHG as compared to an inhabitant of the city of Lille. In 2006, inhabitants of suburbs and peri-urban zones account for two-third of the LMCU population but for three-quarters of the total transport GHG emissions.

GHG emissions per individual per day

> Growing gaps

This phenomenon has become more and more important as shown by the evolutions of individual GHG emissions since 1987.

Emissions mostly and strongly increased in peri-urban areas over the period (+ 46 %) when the increase was lower in downtowns (+ 10 % in Roubaix/Tourcoing and + 5 % in Lille). The gap in polluting travel behavior between urban and Periurban inhabitants, already existing in 1987, is growing over time.

Enlargement of the assessment to all traffics (internal, transit and exchange for both passengers and freight) no compensation but contrasted evolutions

Methodology

The Mobility Environmental Diagnosis (MED) enlarges the EEBT assessment by completing it: the updated methodology accounts for the internal trips of the inhabitants as in the EEBT, but also on the one hand includes the exchange trips of these inhabitants and all individual transit trips, and on the other hand all types of freight traffics (internal, exchange and transit).

As the EEBT, the MED computes energy consumption and emissions for both GHG and local air pollutants. The assessment is still carried at the global geographical level of LMCU, the Urban Community of Lille, and all the trips made outside this area are not taken into account. The geographical boundaries of the environmental assessment are the main difference between the MED and the "territorial Carbon Balance" (Bilan Carbone© in French, according to the methodology developed for the French Environment and Energy Management Agency 12 ). The latter only includes internal and exchange trips directly related to running activities on the Urban community Territory -but the total GHG emissions are computed on the overall trip, and by including emissions related to production of the vehicle and fuels.

About internal trips of LMCU inhabitants, MED relies on the previous EEBT methodology of assessment. But for the other types of traffic (passengers trips of transit and exchange, freight traffics), the computation of emissions is done at an aggregate level by multiplying traffic data (travelled kilometers) by unitary emissions coefficients (emissions for one travelled km).

The MED is a global environmental assessment aiming to give a exhaustive picture of energy consumption plus GHG and local air pollutants emissions to be related to the entire transport flows by extending the assessment to all types of transport traffics on the territory of the considered urban area.

Contrary to the «internal» EEBT (allowing detailed analyses), the main goal of the MED is on the one hand to determine the relative weights of the different transport modes and of the different types of traffic in the total emissions assessment, and on the other hand to establish the temporal distribution of their relative contributions to pollution. Thus, the present extended methodology doesn't aim, unlike the EEBT, at identifying and analyzing the different determinant of energy spending related to transport and air pollution, and GHG emissions.

The MED method is not yet officially validated on various local cases and standardized as the EEBT is. The MED relies on a 4-step methodology:

Inventory of all the traffics to take into account;

Collection of traffic data;

Research of the relevant and updated emissions factors Computation of energy consumption and emissions.

Results: striking growth of GHG emissions in Lille Region

The low increase of CO2 exhausts and of fuel consumption observed for the 1998-2006 period in Lille Metropole marks great disparities in the evolution trends among the different types of traffic. In this way, the balance of passengers is slightly decreasing: it results in a decreasing contribution of the trips made by the inhabitants of the Lille Urban Community, partly compensated by a strong rise of the contribution of passengers exchange and transit flows. The contribution of freight transport to emissions has sharply ridden over the period. And in any case, road traffic remains the main energy consuming mode and the more polluting mode generating, with, for example, more than 90 % of CO2 emissions.

• A/ More and More GHG emissions are related to transport: an increasing trend

The Carbon Balance conducted on the territory of LMCU 13 has shown the importance of the transport sector in the GHG emissions on the Lille urban community area (43 % of total).

The MED shows that, all in all, transport sector in 2006 is accountable for around 4,430 tons of GHG emissions by average working day. This represents a slight increase by 5 % compared to 1998.

Freight transport participation to GHG emissions is considerable: it accounts for one third of the total emissions on the LMCU area. But as regards the energy consumption related to transport we can note a relative stability over the period (+ 2 % between 1998 and 2006). • / Disparate situations according to individuals traffic types If the emissions of GHG in relation to passengers traffic are characterized by stability over the period (-1 %), discrepancies exist between on the one hand the striking rise of emissions generated by passengers exchange and transit traffics (respectively + 24 % and + 19 %) and on the other hand the diminishing level (decrease) of emissions related to the internal trips (-7 %).

Stabilization of internal traffic allows benefiting from technological improvements of (passenger cars) engine. The greatly dominant share of internal flows among the totality of passenger transport (81 % in 1998 and 79 % in 2006) explains the stability of GHG emissions related to passenger trips.

• C/ Freight transport growing strongly

Freight traffic presents a very different structure compared to passengers one: in 2006, the composition of the traffic was of 8 % for transit, 30 % for exchange and only 12 % of internal flows related to urban logistics. All in all, freight traffic increased between 1998 and 2006, but transit and exchange increased the most: + 36 % for exchange vs. + 31 % for transit and only 3 % for internal traffic.

Energy consumption and GHG emissions are divided into three equal shares among the three types of freight traffics, in spite of the unequal distribution mentioned above. This is explained by the fact that one kilometer travelled on an urban way consumes more energy that one kilometer travelled on highway (partly due to a speed effect).

• D/ Road modes remain mainly responsible for all polluting emissions

Road traffic remains the main cause of air pollution and GHG emissions related to transport in urban areas.

For passengers as well as for freight, road mode is greatly prevailing among trips. Car (driver and passengers) accounts for 79 % of passenger flows (in passenger*km) in 2006, this share being slightly decreasing in comparison to 1998 (81 %). The contribution of car to polluting emissions is more important: car generates 95 % of GHG emissions, and from 91 % (volatile organic components) to 96 % (carbon monoxide) of local air pollutants related to the passengers' trips.

In the same way, 84 % of freight are brought by road in 2006 (flows in tons*km), and the share is increasing with respect to 1998 (82 %), generating 98 % CO2 emissions related to freight transport.

In addition, the strongest increases observed in traffics are occurring in road transport: > Road traffics generated by exchange and transit trips of passengers with the Lille Urban Community have increased by + 30 % over the period; > Road traffics generated by freight transport have increased by + 27 % in the same time.

Conclusion

The application developed here in the case of Lille urban area proves the feasibility of the MED methodology, upadating and extending the former methodology of EEAT we previously developed.

In order to assess the global contribution of transport to greenhouse effect (and climate change) (for example for environmetal assessments of "urban mobility plans"), a relevant evaluation should a priori consider all kinds of traffic and the complete length of the trips, including the part made outside the concerned area: precisely GHG emissions by transport activities is then twice higher than the ones identified by the MED. Thus, a particular care should be devoted to exchange trips and their relative environmental impacts.

Indeed this aspect should not to be neglected: the part of the exchange trips made outside the territory o Lille Urban Area. The MED methodology does not take into account the length of the exchange trips that is done only in the perimeter of the LMCU area. For example, considering exchange trips of passengers made by car, the MED only includes the 10.5 kilometers travelled on the Lille Community territory for the computation of the GHG and air pollutants emissions when the total length of the trip is of an average of 49 km.

The two dimensions of the issue of polluting air emissions makes essential and imperative to carry on different types of actions (political measures on urbanism and on transport sector) in order to get results and emissions reduction at the scale of Lille region but also in order to meet national and international commitments on climate change and nature preservation.

The strong decrease of the emissions of the local air pollutants should continue owing to more and more restrictives norms. However, the impacts of these norms will not fully matter before twenty years because of the complete renewal of the car fleet. Even if the 2006 level of emitted particles was over the 1987 level, the emissions should be reduced with the spreading of filter particls in the car fleet. Technical improvements would obviously not be enough to reach the aimed and desired decrease of GHG emissions of 20%-30% for 2020 for the transport sector and moreover the decrease by 75 % for 2050. Such a reduction can be reached only with strong political actions aiming to reduce car dependency by a better spatial organization of the activities on the territory and by promoting low carbon modes and public transit. The success of these policies relies on changing attitudes and travel behaviors, at the individual and the collective level towards an eco-friendly standing. Eco-mobility implies to change our way of thinking trips.

  « internal » trips 267 155 « non internal » trips 93% 7%internal trip means that the origin and the destionation of the trip are within the considered urban area. By extension, internal individuals and internal households correspond to individuals and households, for which all registered trips are internal.

  The situation is different when considering GHG emissions in relation to transport on the Lille Urban Community territory: computations show a rise by 45 % between 1990, based year for climate change policy goals, and 2006. Focusing only on the transport sector, reaching the target defined by these policies imposes to divide by 6 the GHG emissions compared to 2006 on the LMCU area.The 4 factor of 1990 -a decrease by 75% of GHG emissions by 2050 -then becomes a 6 factor relatively to 2006. By 2020, the expected effects of the renewal of the ancient car fleet by new and less polluting cars should only allow to reach the 1990 level, under the assumption of a stabilization of all road traffics at their level of 2006.

Evolution 2006/1987 of consumption and GHG emissions of internal trips made by LMCU inhabitants 0 50 100 150 1987 1998 2006 Energy consumptio n GHG Evolution 2006/1987 of CO, NOx and VOC emissions of internal trips made by LMCU inhabitants 0 50 100 150 1987 1998 2006 CO NOx VOC

  These technological advances were not sufficient to balance the sharp increase of internal road traffic between 1987 and 1998. At the opposite, the stabilization of this traffic during the next period between 1998 and 2006 allows to fully enjoy their benefits.However, if the energy consumption related to internal trips made by car by LMCU inhabitants decreased by10% between 1998 and 2006, it remains in 2006 5% over the 1987 level.

		Euro 1	Euro 2	Euro 3	Euro 4
		1993	1996	2000	2005
	Oil		maximum emissions (g/km)
	CO	2,72 (4,05) 2,20 (3,28)	2,30	1,00
	HC	/	/	0,20	0,10
	NOx	/	/	0,15	0,08
	COV+NOx	0,97	0,50	/	/
	Diesel oil		maximum emissions (g/km)
	CO	2,72	1,00	0,64	0,50
	NOx	/	/	0,50	0,25
	COV+NOx	0,97	0,90	0,56	0,30
	Ps	0,14	0,10	0,05	0,025

The spread of technological improvements (catalytic exhaust pipe, particles filter, etc.), which have led to the decrease in unit consumption and emissions of road vehicles, have been greatly accelerated by the adoption of more and more restricting European Norms. The latters, since the beginning the 1990s, impose more and more lowered (about every four or five years) maximum level of emissions for regulated local pollutants.

Share of soft modes in the number of trips, distance and GHG emissions

  If we consider the unit of the travelled kilometer, car remains the most polluting mode -at the vehicle level-in terms of GHG emissions. But -at the individual level-(taking into account the occupancy rate of the vehicle), and then considering the passenger*km unit, one kilometer travelled by one individual by car emits in average 172 g of GHG.In comparison, the average unit GHG emission factors by passenger*km are finally: 72 g for motorized two-wheel vehicles and 42 g for Public Transit.

	100%
	80%
	60% 40%	65%	92%	100%	Other modes
	20%	35%			Soft modes
	0%		8%	0%
		Number of trips	Distance	GHG emissions
		Share

of public transports in the number of trips, distance and GHG emissions

	100%
	80%
	60%	91%	83%	95%
	40%
	20%
	0%	9%	17%	5%
		Number

of trips Distance GHG emissions Other modes Public transports But

  'Public Transit' is not a homogenous category in terms of energy consumption and emissions. Disparities are noticeable: subway and tramway, running with electrical energy (largely on peut retrouver le % dans mon wctr2007 produced by nuclear power stations in France) have very low level of emissions when the emission factor for bus is of 100 g by passenger*km. All in all, public transit accounts for 5 % of GHG emissions and for 17 % of the travelled distance.

	Share of 2-

wheel vehicles in the number of trips, distance and GHG emissions

	100%
	80%
	60%	99%	99%	92%
	40%
	0% 20%	0.7%	0.9%	8%
		Number of trips	Distance	GHG emissions

Share of different traffics in GHG emissions (2006) 71% 29% Passengers Freight These

  results fit and confirm the trends observed at the national level: the share of emissions related to the transport in the total of GHG emissions at the national level for France was of 21 % in 1990 and has raised up to 26 % en 2006 14 .

		Evolution 2006/1998 of GHG emissions
			by category of traffic
	25%
				+21%
	20%
	15%
	10%
	5%	+5%
			-1%
	0%
	-5%	Total	Passengers	Freight
	• B/
	While GHG emissions are still rising, local pollutant emissions decrease substantially. The assessment for 2006 also shows that local air pollutant emissions, all types of pollutants included, have considerably decreased relatively to 1998: -62 % for carbon monoxide, -35 % for nitrogen oxides, -56 % volatile organic components and -36 % for fine particles.

13 Source : LMCU (Carbon Balance according to ADEME methdology) 14 Source : CITEPA, for Centre Interprofessionnel Technique d'Etudes de la Pollution atmosphérique, in French. CITEPA is an inter-professional network in which relevant and up-to-date information about policy and technology on atmospheric pollution circulates

Passengers and freight, contrasted evolutions over the period

  From 1998 to 2006, GHG emissions related to passenger trips are stable (-1 %). On the contrary, those related to freight trips have strongly progressed (+ 21 %). The share of freight transport in the total of GHG emissions has gone from 25 % to 29 % between 1998 and 2006.

The term was coined by a Ministerial decision issue the 1rst of March 1993.

Abbey DE , Mills PK , Petersen FF , Beeson WL Long-term ambient concentrations of total suspended particulates and oxidants as related to incidence of chronic disease in California Seventh-Day Adventists. Environ HealthPerspect, 94: 43-50 1991

now LTE for "Laboratoire Transport et Environnement", former LEN for "Laboratoire Energie et Nuisances"

For PDU : Plan de Déplacements Urbains, in French

For EMD : enquêtes ménages déplacements, in French

This methodological point is of importance; in particular this updated method does not allow the complete and exhaustive sum (distance-budget, time-budget, energy consumption and emissions) for all the members of the household: the energy and emissions budgets computed with the EEBT are then done only for individual and not at the household level.

In the case of individual modes, the description of the fleet owned by the households allows.to assign the technical characteristics of the vehicle to the trip.

the classical (or usual) weighting system is used to affect a certain coefficient to each member of the household. By doing so, it allows to compare living standard for same size or differently composed households. On this schedule, the number of individuals is brought back to a number of consumption units (CU) (value: 1 CU for the first adult of the household; 0,5 UC for the other members over 14 years old and 0.3 for the children less that 14).


Cecilia Cruz
email: cecilia.cruz@inrets.fr

How is own account transport well adapted to urban environments?

Keywords: urban freight, own account transport, density of deliveries, time delivery

Own account transport is commercially invisible but its importance in urban freight is significant: it represents half of deliveries. Generally research efforts focus mainly on thirdparty transportation because data is more available in spite of a lack of urban data. Nevertheless, the organization of transport by a shipper is not the same than third-party transport. The products transported, the constraints, the demand of transport are different. This analysis shows that own account transport is well-adapted to urban areas because of the density of deliveries and an increase of the number of establishments of the shipper who extends its areas of customer and makes profitable its fleet.

INTRODUCTION

It is difficult to define the extent of cities. In France, urban areas are referred to as 'urban units' (unité urbaine),1 when they meet certain morphological criteria (the continuity of the built environment) and surpass a population threshold of 2000 inhabitants. This same threshold is often used in international comparisons [START_REF] Moriconi-Ebrard | Geopolis, Pour comparer les villes du monde[END_REF]. This definition of cities was established by the INSEE 2 in 1954, but as suburbanisation progressed additional definitions were created. In 1997, the INSEE created a new kind of zone called the 'urban area' (aire urbaine) which is composed of an urban hub and a suburban ring (Fig. 1). This second definition of cities, which is the one used in this article, allows for a more functional vision of urban space because it takes employment into account. Through the th WCTR, July 11-15, 2010 -Lisbon, Portugal 2 distinction between urban hub and the suburban ring, it is possible to consider conditions specific to the density of areas without ignoring less dense zones in the urban periphery, which may be home to industries with strong connections to the rest of the urban area. The polycentric dimension of cities is also better accounted for. The urban environment is characterized by a concentration of production and consumption. As [START_REF] Ogden | Urban Goods Movement: A Guide to Policy and Planning[END_REF] said, the freight is "complex and heterogeneous" and means that "there is a multitude of "actors" in the urban freight scene, and therefore a multitude of perceptions of the "problem"." This space is regularly the subject of tensions, from both an urban planning perspective and that of human and freight traffic. Urban freight transport, which can be defined as all movement of goods within an urban environment, is often considered to be a nuisance because of the predominance of road-based modes. It is nonetheless necessary for the city to function.

There are two basic ways to organize freight transport: a shipper may organize and carry out transport using its own means, which is referred to as own-account (OA) transport; otherwise it uses an external transport service provider, which is called third-party (3P) transport. Ownaccount transport is rarely studied, and literature on the subject is limited. In 1992, Ogden published a book on urban freight but own account transport is not analyzed in details. The lack of information is probably due to the difficulty of identifying and contacting own-account shippers. These firms see freight transport as an essential, strategic aspect of their work, 3and as such they are often hesitant to reveal details.

The studies on own-account freight transport that do exist tend not to mention the fact that this kind of organisation is quite urban. However, its presence in the city is far from negligible: in France, the Transport and Goods in Cities surveys4 have shown that the majority of urban delivery and pick-up operations are done on an own-account basis (Patier, th WCTR, July 11-15, 2010 -Lisbon, Portugal 3 2004). More than three fourths of paths 5 in Bordeaux and Marseilles are handled on an ownaccount basis, and half of those in Dijon [START_REF] Patier | La logistique dans la ville[END_REF]. Thus, the urban territory seems to be conducive to own-account shipping. In this article, we will explore the reasons for using ownaccount shipping in urban environments, and the relevance of its use in a context where the overall share of own-account traffic is decreasing (in France, its share dropped from 26% of tonne-km in 1995 to 16% in 2007; in Germany, the share fell from 35% to 21% over the same period 6 ). Though its share of all traffic is diminishing, own-account transport is still very present over short distances. In France, its share over short distances has been increasing for two decades [START_REF] Cruz | La région, échelle de pertinence du transport pour compte propre en France : état des lieux et éclairages par les caractéristiques du service de transport[END_REF]. In Germany, 47% of tonne-km travelling less than 50km were own-account, and in the UK the figure is 45% (2007).

In 2004, the INRETS 7 conducted an original survey on transport practices (Inset 1). In this survey (ECHO 2004) shippers were questioned about their shipping practices, revealing connections between the production system and transport. Another objective of this survey was to take the increasing complexity of transport chains into account. To do so, shipments were traced from their departure point to their destination, revealing the different steps that a single shipment passes through to reach its recipient. Here, we have complemented this quantitative approach with a more qualitative case study of a specific firm that uses ownaccount transport, allowing us to examine the relevant spatial extent of this kind of shipping.

Inset 1: the 2004 ECHO survey Reliance on own-account transport is the result of logistic constraints which are specific to those sectors that use it. First, we shall see how the concentration of activity in the city makes it a place where shippers can achieve cost savings by managing their own transport. Secondly, we will evaluate the role that timing plays in this choice, and the implications at the metropolitan scale. Next, we will attempt to identify which territories are most relevant for the use of own-account transport through a case study. Finally, we will examine the role of legal constraints on transport choice, looking at both vehicle type and delivery hours, and discuss transport supply in urban environments.

5 Path: All points passed through by the delivery driver to pick up or deliver goods. 6 Data: Eurostat 7 The French National Institute for Transport and Safety Research 3000 firms were surveyed, representing a total population of more than 69,000 firms Scope: All firms with 10 or more employees belonging to the industrial sector (apart from mining) and the wholesale trading sector. Only sending shipments of at least 1 kg were surveyed. Principle: Monitoring shipments sent by the shipper until they reach the consignee and reconstructing the entire transport chain. A shipment is a group of goods sent between one consignee and one consignor.

Goals: -

To link shippers" production activity to their choice of transport, -To monitor the shipper"s shipments until they reach the consignee in order to perceive the multiplicity of journeys and modes of organization. th WCTR, July 11-15, 2010 -Lisbon, Portugal 4

MANY FIRMS USING OWN-ACCOUNT TRANSPORT ARE CONCENTRATED IN THE CITY

The urban environment is conducive to the use of own-account shipping. The 2004 ECHO survey shows that own-account shipments are predominantly urban. 92% of own-account shipments have urban points of origin, and 80% have urban destinations. 50% of ownaccount shipments are carried out within a single urban area8 . These figures confirm the urban character of own-account transport. In our analysis, we will concentrate on flows within a single urban area in order to highlight the local role of own-account shipping.

The use of own-account shipping is related to economic sector

To understand goods mobility in urban areas, one must decompose the urban economy into sectors, as each type of business generates a different volume of flows with different shipment frequencies. As Dablanc has observed (2007), within a business sector there is no real difference from city to city. From a logistic point of view, firms of the same size and sector will function almost identically in any city in France. The major differences appear from one sector to another. Knowledge of the interactions between freight activity and economic structure is essential to understand the mechanisms of urban freight transport [START_REF] Ogden | Urban Goods Movement: A Guide to Policy and Planning[END_REF][START_REF] Woudsma | Understanding the Movement of Goods, Not People: Issues, Evidence and Potential[END_REF].

Differentiation by sector is also useful in explaining reliance on own-account shipping, as observed by [START_REF] Patier | The part of own account transport in urban logistics[END_REF] (Fig. 2). It is essentially retail, wholesale, the crafts, and services who rely on own-account shipping for more than half of their needs, and this figure can be as high as three fourths for small shops (Chiron-Augereau, 2009). These business sectors have specific needs in terms of reliability, and timing is essential. Because they are more serviceoriented than industrial, they need to offer high-quality service or ensure proper reception of supplies (in the case of own-account consignee). th WCTR, July 11-15, 2010 -Lisbon, Portugal 5

Figure 2: Management of delivery operations by type of business. Source: [START_REF] Patier | The part of own account transport in urban logistics[END_REF] One explanation for the preponderance of own-account transport in urban areas is the location of its main users: in 2008, 83% of wholesale establishments were located in urban areas, whereas only 72% of industrial sites were located there 9 . Some characteristics of own-account freight are explained by the types of business involved (wholesale and retail) which are more likely to carry out shipments in delivery runs. Ownaccount transport makes up 82% of multi-stop delivery runs carried out within a single urban area.

Business sector is the main factor explaining why a firm chooses one kind of organisation over the other. However, the geographic configuration of the city also affects the circulation of goods: for example, the existence of a bypass road may encourage use of own-account transport, as infrastructures of this kind can reduce trip time, and thereby reduce costs.

The role of density in own-account transport organisation

Urban freight varies according to a city"s geographical areas. City centres concentrate a high density of freight movements: 5,000 to 30,000 deliveries and pick-ups per km² per week for European cities 10 . According to [START_REF] Patier | La logistique dans la ville[END_REF] one third of a conurbation's pick-up or delivery operations occur in the hypercentre. 11 The structure and compactness of the urban context encourage the use of own-account transport, which is particularly present in dense urban areas. According to the ECHO survey, 72% of shipments carried out within a single urban hub are own-account. This observation is not limited to France: according to data from the Politecnico di Milano The hypercentre is characterized by a historic centre with narrow streets, a strong concentration of employment, and mixed use, rarity of space which leads to growing land costs. (...) The concentration of independent or franchised shops leads to dense traffic." [START_REF] Patier | La logistique dans la ville[END_REF] th WCTR, July 11-15, 2010-Lisbon, Portugal 6 (2000) 12 , 63% of deliveries and pick-ups in the centre of Milan are own-account. The proportion of own-account shipments is higher near the centre of cities: in a 2004 study on the Emilia-Romagna region [START_REF] Bestufs | Du transport de marchandises en ville à la logistique urbaine, quels rôles pour un opérateur de transports publics urbains ? Le cas de la RATP[END_REF] we see that the use of own-account transport decreases as geographic scope increases. Of all own-account shipments in this region, 51% are in the district of Bologna, 34% in the province of Bologna, and only 15% of own-account shipments are at the regional scale. Thus, own-account shipping is used more frequently in dense parts of the urban area; this fact is strongly related to the business sectors which manage their own shipping.

TIME: AN ESSENTIAL FACTOR FOR URBAN FREIGHT, AND A KEY ELEMENT IN THE ANALYSIS OF OWN-ACCOUNT TRANSPORT

Taking the client's needs into account: more reactivity and better service

Timing is essential in urban freight transport: the density of commercial activity and consumption amplifies the role of just-in-time (JIT) logistics, which are all the more valuable in that urban environments are close to consumers. Maximum delivery leadtime requested by clients can be a good indicator of JIT practices and requirements for tight control over freight transport. We observe shorter maximum delivery leadtime requested on own-account shipments: for wholesale own-account shipments within a single urban area, the mean was 1 day as opposed to 2.5 days for wholesale shipments carried out by third parties; for industry own-account shipments within a single urban area, the mean was less than 3 days as opposed to less than 32 days for industry shipments carried out by third parties 13 . This demonstrates that own-account shipments participate more in low time limit production systems, where clients expect rapid delivery or pick up their own orders, as in the case of the Rungis, a wholesale market for fruits, vegetables and agricultural produce in Paris Urban area.

For 50% of shipments of own-account transport, the maximum delivery leadtime requested is 24h versus 48h for third-party for all of activities. Reductions in shop inventory have repercussions on intermediate links (wholesalers), who serve as a buffer between industries reducing inventory and shops that wish to do likewise. Thus we observe that wholesalers who rely on own-account transport for their shipments within a single urban area retain more days of inventory: on average, 46 days as opposed to 22 days for those who use third party shipping. Intermediaries play an increased role in this fragmented production system [START_REF] Guilbault | Demand for transport and production systemsshipper surveys in France in 1988 and 2004[END_REF].

Transport reliability is a major issue for this kind of business. [START_REF] Thompson | Chapter 25 City logistics and freight transport. Handbook of Logistics and Supply Chain Management[END_REF] remark that retail shops have a stronger need to be supplied (for example) with fresh products, which necessitates higher shipment frequencies, thereby increasing the number of deliveries over restricted time windows. In fact, we observe that shipper-recipient relationships are stronger among wholesalers who use own-account delivery: on average the annual number of shipments sent between each origin/destination pair within a single urban area is 1086, versus 173 for wholesalers who use third-party shipping under the same conditions 14 . The median of the annual number of shipments sent between each origin/destination pair within a single urban area is 250 shipments annually for wholesalers using own-account shipping for the surveyed shipment, and 30 for wholesalers using third-party shipping 15 .

The difference between these two types of transport organisation increases with urban density: for shipments within a single urban hub, the average client requested a maximum delivery time of 1 day for wholesale shipments versus more than 3 days for third-party 16 . For industry own-account shipments, the average is less than 4 days, versus 54 days for thirdparty 17 . Spatial proximity is essential to satisfy this sort of demand. The figure helps us to understand this: the left part link the production with the time and the consequences in terms of uncertainty, the right part illustrates the phenomenon in spatial terms. As Rodrigue has shown (Fig. 3), while increasing the number of links in logistic chains may reduce the higher level of uncertainty and offer more proximity, it also implies an increase in inventory costs, as discussed above. Differences are also visible with increasing density on a given shipperrecipient link: for shipments within a single urban hub, the annual number of shipments is higher for wholesalers using own-account shipping (1260) than for those relying on third parties (217) 18 . The denser shipment links are, the more it is in a firm's best interest to carry out transport on its own account. In own-account organisation, client relationships are important, but recipients may be more than just clients: for firms that use own-account transport for shipments within the same urban area, the share of shipments that are destined for other sites of the shipper's parent firm or group is 14% on average, as opposed to 19% for firms using third-party shipping. This demonstrates that own-account shipping is not preferred for intra-establishment exchanges within a firm or group.

Delivery schedules discourage mutualisation: two different ways to deliver

Figure 4 shows that unloading takes longer in the sectors that use own-account shipping most, except for very large retail centres whose high volumes lead to longer times. Users of own-account transport take their clients' specific expectations into account: for example, a manufactured products wholesaler may offer inventory storage, or a Parisian caterer might offer personalised delivery schedules and goods. Specialized service increases unloading time, which takes an average of 47 minutes for own-account shipments (direct trips carried out by vehicles less than 3.5 T Gross Vehicle Weight Rating) versus 26 minutes for thirdparty shipments of the same kind. For delivery runs with less than 30 stops, the average own-account unloading time was 13 minutes, versus 9 for third-party [START_REF] Patier | The part of own account transport in urban logistics[END_REF]. This observation holds independent of vehicle dimensions: the gap between own-account and third-party unloading time persists for larger vehicles. Thus we see that own-account and third-party transport imply different ways of delivering due to special client requirements. This is also true from the perspective of delivery schedules. For example, drivers for a caterer in the Paris region start very early in the morning (5AM) and end their shift at around noon. At this point other drivers begin a second shift that ends at 8 PM. They may be called upon to carry out operations at unusual hours for special events. Considering the unusual schedules and trips involved, it is difficult to find a suitable third-party carrier.

The delivery driver's job is unique. The maps in figures 5 through 8 represent delivery runs made by such drivers in urban environments. They are from the Transport and Goods in Cities surveys (TMV) carried out by the Transport Economy Laboratory (LET) in Bordeaux (1995) and Dijon and Marseilles (1997).

Figures 5 and6 show the path of own-account delivery runs. These drivers work morning shifts: 7 to 9 AM for the meat delivery driver and 6 AM to 1 PM for the frozen foods distributor. The meat delivery points are scattered throughout the city, whereas the frozen foods deliveries are more concentrated toward the centre. This difference can be explained by the clients: kosher butchers are not very numerous and are dispersed throughout the urban area, whereas frozen foods retailers are also located throughout the city, but are distributed more evenly, which makes concentrated delivery runs possible. Another point is that own-account transport is better adapted to certain business' schedules.

For example, because a grocery wholesaler's delivery runs are done early in the morning, 20 it was more appropriate to opt for wholesale-specific labour restrictions than those of the transport industry. The 39-hour weekly limit fits the schedule, e.g. 5 AM to 12 noon with a half-hour break. Delivery drivers also rarely accumulate 4.5 hours 21 of driving in one daythey drive a total of about 100 km around their origin.

20 Interview with the transport manager of a grocery wholesaler, 6 May 2009. 21 Beyond 4.5 hours of driving, drivers are legally required to take a break of 15 minutes minimum.

THE RELEVANCE OF OWN-ACCOUNT TRANSPORT USE BASED ON SHIPMENT FREQUENCY, TONNAGE, AND ACCESSIBILITY

Here we present a case study on a manufactured products wholesaler. The firm studied uses own-account transport in the Paris region (Ile-de-France), and occasionally in the neighbouring Oise département (deliveries to one municipality in 2007). It is important to note that this firm does not sell products which might require the use of specialised delivery equipment. Own-account transport is used for quality of service reasons. The firm considers client relationships to be essential, and provides the complementary service of storing merchandise after orders, delivering it whenever the client is ready. Own-account transport is justified by the desire to assure delivery within 24 hours. Rapidity is a way to stand out among the competition, and thus own-account delivery is a selling point.

30% of the firm's shipments are own-account. Until 2001, this shipper handled all of its own shipments within the Parisian region. Then, the business redefined the borders of its ownaccount service zone in order to reduce transport costs. We clearly see that the areas with the highest frequency of deliveries (up to 94 shipments per week) are those that continue to receive own-account service (Fig. 9 and 10). The spatial distribution of tonnage (map not presented here), is similar to that of delivery frequency. The own-account service zone was largely defined by the volume of merchandise delivered. The firm's market is essentially the Parisian region; in other French regions, volumes are less concentrated.

13 These maps illustrate the fact that shippers rationalize costs, and that own-account shipping is a conscious strategic choice, rather than a simple decision made without knowledge of the environment.

We have also analyzed all of this firm's shipments (both own-account and third-party) to municipalities in Ile-de-France. Three parameters which affect transport cost (frequency, tonnage, time accessibility) have been calculated for each municipality. As mentioned above, the entire zone is not served on an own-account basis because costs are too high. We have grouped different values for these parameters into four categories:

15

-Category 1 (Own account service very relevant): Municipalities where the shipment frequency is high, tonnage is high, and time accessibility is good (defined as below 1.5 hours from the firm location). Own-account service is advantageous. Certain municipalities situated to the east but not currently in the own-account zone may be economically interesting. High delivery frequency and a location close to motorways allow a faster rotation of equipment and thus better profitability. -Category 2 (Own account service relevant in terms of tonnage and time):

Municipalities where tonnage is high and accessibility is good. Should be studied attentively, as heavy shipments may make service profitable. -Category 3 (Own account service relevant in terms of tonnage or of time):

Municipalities where either tonnage is high or accessibility is good. Own-account delivery is less advantageous. -Category 4 (Own account service not relevant): Certain municipalities are located away from motorways and not relevant, as all shipment parameters for these locations are negative.

While adjustments could be made to the initial service zone (cf. Fig. 9), they are minor (cf. supra category 1).

16 This case study shows that the spatial distribution of own-account shipments is not uniform throughout an urban area, and that the density of clients (and thus of shipments) helps explain reliance on own-account transport.

REGULATORY CONSTRAINTS SLOW THE DEVELOPMENT OF SPECIALISED PROFESSIONAL CARRIERS

The implementation of goods transport policies lacks coherence in urban areas. [START_REF] Dablanc | Transports de marchandises en ville, une gestion publique entre police et services[END_REF] has shown that legal constraints in the Paris region are heterogeneous. Since 1996 22 French urban areas must elaborate Urban Travel Plans (PDU) which include a section on freight. They are thus responsible for defining transport policy orientations. However, individual municipalities retain (police) power over vehicle traffic, and often take action which is not coherent with the urban area's general policy, or even neighbouring municipalities' traffic rules. Municipal ordnances often restrict access to heavy trucks. The resultant superposition of rules in the urban environment is not conducive to the emergence of service providers offering a true alternative to own-account transport.

It is interesting to note that the firm presented in the above case study records legal restrictions (such as vehicle size limitations) in their client database as soon as this information is known, which allows better delivery organisation. When the first delivery is made for a customer's first order, it is possible that the delivery vehicle is prohibited from using the street where the client is located. This system allows the firm to avoid repeating such errors. Knowledge of legal restrictions within the delivery area is necessary to optimise shipping and ensure high reliability of delivery times. Firms which rely on own-account shipping develop their own tools to increase efficiency and reduce the risk of additional transport costs.

Transport in urban environments is unique because activity is concentrated, causing specific problems. While this space is particularly susceptible to congestion problems, we have also seen that it requires the most reliable transport due to the large number of clients. Nonetheless, few large carriers handle their own deliveries in urban areas, and parcel delivery firms outsource service in major cities. These firms respond to the trend toward shipment fragmentation by grouping and degrouping small packages, and as most of their principal recipients are in urban environments, they contribute to the dominant role of subcontracting. Outsourcing certain links, particularly the final one, helps lower total transport cost and concentrate resources on activities that are more profitable than transport and logistics organisation. Research on outsourcing in urban environments (Cruz et al., 2009) shows that this practice is common, and that external factors beyond carriers' control such as traffic congestion also play a role. As traffic conditions worsen, drivers' tours lengthen and firms find it safer to employ a sub-contractor. Under these conditions, it is difficult to assure personalized service for the clients who constitute the majority of their demand.

According to a report from [START_REF] Pipame | La logistique mutualisée : la filière « fruits et légumes » du Marché d[END_REF], a large share of fruit and vegetable distribution in Paris is own-account. Legal restrictions on the transport of fresh products impede delivery optimization. Different kinds of products (meat, cheese, fish, etc.) cannot be mixed during th WCTR, July 11-15, 2010 -Lisbon, Portugal 18 transport23 . This study on Rungis Market underscores the lack of multi-compartment transport services. During our interviews, we encountered a case where a wholesale restaurant supplier using own-account transport was developing a multi-compartment vehicle to better solve this problem. This case shows that when transport supply does not respond to shippers' needs, they do not even consider outsourcing to be an option.

One French group called Star Service specifically deals with last-mile logistics for controlledtemperature perishable goods, and is diversifying its business through subsidiaries such as Toutadom, which delivers fully prepared meals. Nevertheless, this kind of large urban carrier is quite rare, with most outsourced flows handled by small organizations. Differences do exist between cities of different sizes and in different geographic locations. For example, cities that are subject to strong seasonal variations (such as those in the South of France) have high rates of outsourcing. The size of cities seems to be an influential variable (Cruz et al., 2009;[START_REF] Raia | La sous-traitance dans le transport de marchandises en ville : acteurs, déterminants, spécificités selon les villes[END_REF].

The transport supply is essentially composed of single-employee businesses, and does not seem to be conducive to the externalisation of what are currently own-account shipments, considering the importance of reliability and the shipment timings required by own-account transport users. The difficult conditions in urban areas seem to make them less attractive for professional carriers, and the city may therefore be a privileged zone for own-account transport.

From a sustainable development perspective, it is appropriate to explore the possibility of mutualising own-account shipments even if it is unauthorized yet in own account transport. In France, as in other European countries, several urban logistic experingents have been carried out in an attempt to reduce flows in an urban area. The principle is to mutualise flows through a logistic platform. This allows savings on transport costs, but these savings are not sufficient to compensate for those imposed by additional transloading [START_REF] Patier | La logistique dans la ville[END_REF]. A shift to this kind of platform would probably reduce quality of service and reactivity for ownaccount shippers, if we take the additional transport steps into account.

CONCLUSION

Own-account transport is used in urban environments because this is where its principal users (retailers) are often located. However, we find that density plays a role, and observe differing levels of use across urban areas. The case study presented here illustrates the role played by shipment density on the use of own-account transport. Own-account service is certainly advantageous at this scale due to inadequate supply of urban freight services. Spatial proximity is not the only relevant criterion for defining zones where own-account transport is advantageous, as time accessibility has a considerable effect in urban areas that experience significant congestion. th WCTR, July 11-15, 2010 -Lisbon, Portugal 19 Own-account shipping is a means for firms to ensure the reliability of their shipments; third parties' obligations to other clients can cause delays, and urban shipping requires rapidity. It is a tool firms use to manage complex urban logistics without increasing transport costs exponentially. For professional transport suppliers, short trips are also less profitable.

Figure 1 :

 1 Figure 1: Two ways to define the extent of cities: the urban unit and the urban area

9

  Data: Sirene-INSEE 10 Data from Urban Freight surveys (Laboratoire d"Economie des Transports) Internet site : http://www.transportsmarchandises-en-ville.org 11 "

Figure 3 :

 3 Figure 3: The complexity of a logistic chain and its effects on uncertainty. Source: Rodrigue, 2006

Figure 4 :

 4 Figure 4: Unloading time according to business type. Source: Patier, 2002

Figure 5 :Figure 6 :

 56 Figure 5: Path of a kosher meat delivery run in Marseilles (7-9 AM) 19 . Source: LET

0Figure 7 :

 7 Figure 7: A parcel delivery driver's tour in Dijon (8:15AM-12PM). Source: LET

Figure 9 :Figure 10 :

 910 Figure 9: Distribution of own-account deliveries by a wholesaler in Ile-de-France in 2007.Source: data from the firm

Figure 11 :

 11 Figure 11: Relevance of service to municipalities in Ile-de-France. Source: data from the firm

According to the INSEE (French National Institute of Statistics and Economic Studies), more informations : www.insee.fr

21% of small businesses (less than 19 employees on the scope of ECHO survey 2004) have their own fleet (Source: ECHO survey)

"Enquêtes Transports de Marchandises en Ville" carried out in Bordeaux in 1994 and in Dijon and Marseilles in

For methodological reasons, our calculations did not allow the inclusion of multipolar municipalities (those which are part of several urban areas). This would probably increase the proportion. Also, the scope of this survey did not take construction materials businesses into account, which are particularly strong users of own-account transport. Thus, the proportion of own-account shipments within a single urban area would be increased.

th WCTR, July 11-15, 2010 -Lisbon, Portugal

th WCTR, July 11-15, 2010 -Lisbon, Portugal 12

National Transport Council, 2004, Programme national marchandises en ville et guide «Une voirie pour tous», Report on work by the "Road sharing" group.