Tristan Guilloux
email: tristan.guilloux@developpementdurable.gouv.fr

Mathieu Rabaud

Cyprien Richer

The role of French mobility surveys in the transport policy-making

Keywords: Mobility, Transport policy, Household Travel Surveys (HTS), urban planning Résumé Mobilité, Politique de transport, Enquête Ménage Déplacement (EMD), Planification locale

Mobility datasets are increasingly used to inform about transport policies and to objectify decision-making. It becomes an European Union issue as several research projects have been undertaken to attempt to harmonize data collection and to carry out a mobility database at an European level. France has been experiencing this harmonization since 1976 through a standardized method and 150 local household travel surveys (HTS) have been implemented. Political science has demonstrated that technical instrumentation to implement a policy, such as statistical system, is not "neutral"; it is the place of political struggles but also the mirror of the current policy agenda. This paper will address the role of the French local HTS in the definition of transport strategy and planning at a local level as well as at the national one. This issue will be addressed in three directions: the method of data collection and its evolution, the layout of the surveys carried out and the typology of the uses of the surveys . In short, with this paper we wish to inform of the importance of taking into account the way mobility indicators are built to guide policy makers in their choice.

Introduction: historicizing 2 the production of mobility data

When it comes to defining a transport policy across an urban area, knowledge of the demand for daily trips -also called daily mobility -is the essential complement to the inventory of road infrastructure and public transport services. It is about knowing all the travelling done on a given day, in a given area, by all residents of the area concerned [START_REF] Bonnel | Prévoir la demande de transport[END_REF]. This knowledge is acquired through statistical surveys of a representative sample of the population, constructed from household and area characteristics, as the use of travel modes and the spatial distribution of travel are strongly influenced by the interaction between household members and the location of their home. In French urban areas, the production of these data has crystallized around a measuring instrument developed by the State and standardized in the mid-1970s: travel surveys.

Travel surveys are based on a method standardized in 1976 and regularly updated since then by State department of transport, to ensure reliable comparisons over time and in space at national level. In 2013, there are 150 surveys in 89 areas, some of them having periodically repeated the survey (every ten years) in order to update the data. At the same time as the number of areas surveyed has increased, variants of the standard methodsuccessively called household survey (HS) and household travel surveys (HTS) -have been developed: Ile-de-France regional transportation survey , medium-sized town travel survey (MTTS) and finally large area travel surveys (LATS). In the following, we will use the term travel surveys (TS) to refer to this whole family of methods.

a. Travel surveys as an instrument of public policy: three directions for analysis

While the results of the travel surveys have led to many publications, both locally and nationally, focusing on mobility in the broadest sense, the surveys themselves remain largely unexamined as an instrument "representing" the reality of an area at the service of a public policy. Yet this approach, focusing as it does on the "political" dimension of travel surveys, is largely complementary to, or explanatory of, the production of data, methodological developments and analyses that are produced. The work of political scientists who analyze the "sciences of government" have developed the idea that policy instruments are not simple levers, but that they help to structure the content of this action and to shape its contours. Much more than this, "[the instruments] are not axiologically neutral and indifferently neutral tools. They are, on the contrary, bearers of values, and nourished by an interpretation of social issues and detailed conceptions of the means of regulation under consideration" [START_REF] Lascoumes | Gouverner par les instruments[END_REF]. By the way they are built and have developed, they are central to a political tempo which considers that "public policy is always defined in relation to change, whether one seeks to curb a change, or, conversely, to promote the transformation of the environment concerned" [START_REF] Muller | Esquisse d'une théorie du changement dans l'action publique. Structures, acteurs et cadres cognitifs[END_REF] .

Regarding travel surveys, the issue can be addressed in three ways. We can look at the very conditions in which the tool is produced, i.e., the method of data collection, identifying through its design and development the institutional issues of mastering technical government knowledge. Analysis of the conditions in which the surveys are carried provides information on their beneficiaries and can provide a panorama in motion of those involved in daily mobility in France. Finally, the use of surveys, which must not be confused with just using the data, refers to the relationship between instrument and public policy that it is supposed to inform.

The genesis of "household surveys," as they were called in the beginning, and during their early years until the early 1980s, is well documented in publications from the 1970s [START_REF] Dupuy | Une technique de planification au service de l'automobile. Les modèles de trafic urbain[END_REF][START_REF] Dupuy | Urbanisme et technique : Chronique d'un mariage de raison[END_REF] and in a more recent study, conducted by Benoit [START_REF] Facq | Les fondements statistiques de la science française des déplacements urbains[END_REF] as part of a Master's thesis at the Institute of Political Studies (Institut d'Études Politiques -IEP) at the University Lyon 2, directed by Professor Gilles Pollet and Fabrice Bardet. B. Facq describes the active role of the technical services of the ministry of transport and its civil engineers in importing, in the 1960s, a method developed in the United States to provide traffic forecasting models. He also highlights the tensions that did not fail to appear in the mid-1970s between a tool developed by the State for purposes of modelling and the appropriation of this tool by local authorities which were gaining momentum and whose requests led to a gradual dissociation between the production of data and building travel models.

Over the period that separates us from those early years, longitudinal analyses were confined to the analysis of results from the use of mobility data (number of trips, mode market share, etc.). They had relatively to say about the relationship between the instrument and public policy. The Master's thesis completed in 2010 by Elsa Alexandre under the direction of F.Bardet should, however, be noted. It undertook such an analysis with reference to Lyon and in the context of environmental policies deriving from the French round table on the environment which took place in Autumn 2007. These monograph-based approaches would be worth developing around the major cities that have regularly conducted surveys, such as Lille, Grenoble, Strasbourg, Bordeaux and many others.

b. The hypothesis of giving local accountability back to public action

The second half of the 1970s and the start of the following decade were marked by the beginning of the decentralization process which saw the transfer of a number of state powers to local authorities, including urban planning and transport organization. In December1982 the constitutional law on the organization of transport in France was enacted: LOTI, the framework law for inland transport. This contribution proposes an approach at national level as well as to local viewpoint. The hypothesis was that the period that began with the standardization of surveys "gave local accountability back to public action" [START_REF] Leloup | La gouvernance territoriale comme nouveau mode de coordination territoriale ?[END_REF]. This analysis pursued what B. Facq had already demonstrated for the first few years of the surveys. It was organized along the three lines outlined above: changes in survey methodology, analysis of the stakeholders involved and the institutional perimeters through the inventory of surveys, and the use of surveys put into perspective with public policy.

c. Contributing from the inside to creating a history: methodological elements

Three sources have been used to provide this history:

• Standardization of methods at national level aims to allow successive surveys to be comparable over time.

To this end, the surveys were archived as and when they were completed, within the scientific and technical network of the ministry of transport. These records are used to provide information on how to carry out the survey: type of survey, the area concerned, people involved, etc. A database on the identity of the surveys was constructed. • The many publications dealing with methods and analyses, both at national and local level, carried out by government departments, local authority project owners or the research community clearly suggest the relationship between this technical instruments and public policies those who implement them. • Oral sources were used, consisting of interviews (or transcripts of interviews) with people involved in conducting the surveys [START_REF] Facq | Les fondements statistiques de la science française des déplacements urbains[END_REF][START_REF] Alexandre | Les Enquêtes-Ménages Déplacements : un outil pour formuler les politiques de transports en commun de la ville durable ?[END_REF]Richer, 2013). These interviews took place when a number of transport ministry officers who had been monitoring the surveys for almost four decades were about to retire. It was important to collect this memory before it faded away; it was even one of the reasons which led to this publication. Although the community of historians continue to debate about the relevance of interviews as oral sources [START_REF] Voldman | Définitions et usages[END_REF], the use of testimonials from professionals is common in historical work on the instrumentation of public policies (Coquand, 1982 ;[START_REF] Beltran | Les électriciens, les gaziers, les hommes de sciences et les autres[END_REF][START_REF] Debizet | Crise et mutation de l'expertise en transport et mobilité[END_REF].

Finally, it should be noted that this "history" is written "from the inside " by officers of the transport ministry. It combines a researcher working in an associated IFSTTAR research team, with a PhD in geography, a CETE Nord Picardie engineer working for 10 years on the surveys, from the development of their method to the analysis stage via the surveys implementation, and the CERTU manager of the group in charge of standardizing methods. This proximity to the subject of the study means that this work must not be confused with academic historical research that requires a certain distance from its subject matter. Nevertheless -and this is how the authors see it-this essay aims to provide the initial foundations for historicizing "French style" travel surveys, which is indispensable to prepare their future.

From household surveys to travel surveys: when the local level is trying to find its place d. From the pilot household survey project to the "standard" household travel survey guide

The "household" travel survey as defined in 1975 provides a photograph of all travel undertaken the day before, with all modes and for all purposes (with rare exceptions) by the inhabitants of a given area. The survey focuses on trips made from Monday to Friday, excluding school holidays, public holidays or special days. Respondents must accurately describe the trips they made on the day before the interview so that, on average, in the area, representative information can be obtained that goes beyond what is considered as "usual" mobility. The basic statistical individual is the household (hence the name of the survey), and all household members aged five and above are face-to-face interviewed at home. The method defines the sampling procedures (size, survey database, geographical breakdown), survey documents, the organization of data collection (time, logistics, checking) and how the information should be used (definition of indicators). From 1976 to the 1990s, around fifty household surveys were carried out under the SETRA/CETUR.

During the 1990s, the SETRA "household" surveys changed and became called "standard method" -and later "CERTU standard"-Household Travel Surveys, widely known by the French abbreviation EMD for "Enquêtes Ménages Déplacement". These details of terminology marked a methodological and institutional turn of events. Until the 1990s, CETUR validated the survey on an a posteriori basis. After the Orleans and Thionville surveys in the mid 1990s were found invalid, CERTU certification became subject to more stringent monitoring. The methodological guide published in 1998 (the first by CERTU) clarifies and strengthens the role of government departments in controlling the survey by formally creating the role of contracting authority assistant (AMOassistance à maîtrise d'ouvrage). This methodological guide was a sign that the household travel surveys were becoming increasingly mature. It also become a more communicative publication, with improved presentation and an illustration on the cover. Since the late 1990s, around fifty "standard CERTU " HTSs have been performed.

e. Travel surveys: local variations and opening up the method

From the 1980s, local governments, mainly through their urban transport organizing authorities, became involved in the surveys and become contracting authorities. But this mainly concerned only the major French urban areas. From the late 1990s, a new urban category began to show interest in this type of survey: mediumsized towns. The method of face-to-face data collection led to costs and resources that they could not afford.

CERTU developed a method of data collection for towns whose urban centre in the sense defined by INSEE (National Institute of Statistics and Economic studies) is less than 100,000 inhabitants. From pilot surveys (Roanne was to be the first in 2000), CERTU published a methodological guide in 2010 called "medium-sized town travel surveys" (MTTS) , also known as EDVM for "Enquêtes Déplacements Ville Moyenne". To make the methodology more accessible, several aspects were modified as compared to the HTSs. The minimum duration of data collection was lowered, and the questionnaire was simplified to include less detail on the use of mechanized modes during trips. All household members were no longer questioned, but only one or two, and only from age 11 and older. Finally and most importantly, the surveys were no longer conducted on a face-toface basis, but by phone. Currently, this new method provides a substantial amount of the information obtained from an HTS, but with a little less accuracy and detail. Most notably, it costs a lot less. The minimum price for an MTTS today is about 60,000 Euros excluding taxes, or about five times less than for an HTS.

With the development of urban sprawl, major cities expressed the wish to carry out surveys on inhabitants living increasingly far away from urban centres. While some chose to use the face-to-face method for large peri-urban fringe areas (Lyon in 2006, for example), others were reluctant for financial reasons, and also because of technical difficulties, since the interviewers were often forced to travel long distance to get to households, without any certainty of getting an interview. The experience with MTTSs made it possible to try out a method (Lille in 2006 and Le Havre, Rennes and Chambéry in 2007) juxtaposing two surveys: an HTS in central urban areas and an MTTS in suburban areas. But this combination of methods quickly raised problems of continuity, including the fact that the face-to-face method was being used to interview people from the age of five, while by phone it was from the age of eleven. In 2011, an addition to the HTS methodological guide for suburban and rural areas was published by CERTU, presenting the unified methodology LATS [START_REF] Certu | Analyse des résultats de l'enquête « Attente vis à vis des EMD[END_REF]. The telephone portion of the survey, more in-depth than for an MTTS, was seen as a complementary survey to the conventional HTS. Children were interviewed from the age of 5 so as not to create a break with the face-to-face part, the use of mechanized transport was more detailed and the survey time was brought up to that of the HTS so that the periods coincided [START_REF] Rabaud | Les enquêtes déplacements standard CERTU : un exemple de conciliation des besoins de continuité méthodologique et d'évolution pour s'adapter aux demandes et aux nouvelles pratiques, 7e colloque francophone sur les sondages[END_REF]. Analysis of the survey production conditions provided better understanding of the interaction between local requests for methods to be adapted to the local and financial context of local authorities, and the State's desire to maintain a national standard (Fig. 1). The increase in the number of surveys was driven by the success of the new methods. Out of 150 travel surveys, there have been 33 MTTSs since 2000 and 14 LATSs since 2006. Counting only the most recent survey in each area, the new methods now account for more than half of the travel surveys, even though they only existed for a few years. Between 2006 and 2013, 70% of travel surveys were MTTSs and LATS, as against 30% for the "conventional" HTS.

The expansion of the "target audience" for household surveys has had an undeniable effect on the number of surveys. These new methods have stimulated the expansion of the original "circle" of towns with surveys.

The effect of the new methods on the pace of travel survey implementation is an important endogenous factor. However, exogenous factors have certainly contributed to the spread and generalization of the need for knowledge of local mobility. Of these, there are of course thea new train of decentralization acts that were enacted at the start of 2000, giving greater powers to the authorities for questions of transport and the strengthening of local planning (-sustainable urban mobility plans (PDU) made mandatory by the government in 1996), or the implementation of the regional integrated development plans, (known as SCOT) in 2000, etc.). More generally, it is the changes in local urban structure through increasing development on the edge of cities, or "periurbanisation", and metropolization together with the rise of new issues such as sustainable development, which seem to be contributing to the improvement in terms of mobility surveys. This movement can be seen through the evolution of survey scopes. With the emergence of new methods, two trends can be observed in the spatial dynamics of the surveys. On the one hand, the first surveys were carried out over smaller and smaller areas: the median population of the first surveys before 1999 was 215,000, falling to 140,000 in 2000. On the other hand, repeat surveys were performed in larger and larger areas. Out of 32 areas that completed at least two surveys, 28 took the opportunity to expand their survey area (Fig. 3).

Fig. 3. Changes in travel survey areas in major towns

Performing a new survey provides an opportunity to change its area in order to take better account of periurban fringes. For the major towns, the survey areas sometimes go far beyond the urban areas as defined by the INSEE. As periurbanisation does not only concern major cities, expanding survey areas also impacts medium-sized towns such as Amiens, Belfort, Bayonne or Roanne whose fringe populations have doubled since the previous survey.

These changes are reflected directly in scale shift of the survey and the institutional dimension of its area. The method stipulates that the CERTU label can be obtained only if the survey area includes at least one urban transport area (PTU). The percentage of this type of survey is falling significantly, whereas surveys on this scale were the norm for the first surveys. If one refers to the other two levels of transport authorities -the Department and the Region-we see that six Departments are now covered (Bas-Rhin, Calvados, Alpes-Maritimes, Bouchesdu-Rhône and the Gironde and Var as a complement to urban surveys) and two metropolitan regions (Ile-de-France regional survey and Nord-Pas-de-Calais Survey as a complement to urban surveys).

The rise of the "urban development" dimension of surveys alongside their primary function related to the design of infrastructure and transport services is evident in the way that the contour of surveys coincides with that of local planning documents on a large scale. About 35 areas correspond to those of the regional integrated development plans (SCOT). This is a scale that is becoming a reference to define the areas of travel surveys. This scale is broader than the PTU and can answer various problems related both to urban travel (with a better understanding of incoming peri-urban flows) and at the level of the urban area and strategic planning.

Finally, there are surveys that do not refer to a single institutional boundary. Eleven areas, containing more than 500,000 people, go beyond the SCOT area of the city centre, sometimes by a large amount (Bordeaux, Clermont-Ferrand, Grenoble, Lille, Lyon, Nancy, Rennes, Rouen, Saint-Etienne, Toulon and Toulouse). Often incorporating several Urban transport areas, these large areas reflect the emergence of the metropolitan question and more generally of dynamics whereby the lived-in space "jumps over" the institutional boundaries [START_REF] Morain | Territoires métropolitains et modes de coopération[END_REF]. One might well argue that these surveys have become a scene for inter-territoriality.

h. Increasing complexity for those taking part

Analysis of how the institutions involved have changed in the presence of the contracting authority for the surveys provides information on "giving local accountability back to public action" and how it opens up to interterritorial considerations. The year 1976 marked a "turning point" because with their "standardization", surveys stopped being fully controlled by central government. The first wave of standard surveys (between 1976 and 1980) was still marked by significant State intervention in project management, through the local public works department (Lille and Lyon in 1976, Nancy in 1976) and funding (50% from central management and a so-called local part from the local public works department). The aim of this devolution was to guarantee that "local agencies and politicians would be interested in having a survey carried out in their urban area" (CETE Lyon [START_REF] Cete De Lyon | Les enquêtes ménages. Note 1 : Bilan des enquêtes ménages réalisées depuis[END_REF]). The handover with local authorities began with joint contracting authority and joint funding shared between the State and the town at the centre of the urban areas (Bordeaux and Toulouse in 1978, Amiens in 1976).

On the political front, the changeover went off fairly quickly. As of the 1980s, there were almost no HTS that were still being managed by the State. The urban public transport organizing authority (known in French as AOTU) took responsibility for HTSs while local funding began to be shared with the "Conseil Général" in charge of the Departements, and in some cases with Chambers of Commerce and Industry. After the 1999 law on the simplification and reinforcement of local cooperation, known as the Chevènement Act, even though the role of the transport authority (with a more community status) remained central to the management of surveys, the sphere of the partners involved in the set-up widened considerably.

The legitimacy of the agency traditionally responsible (the transport authority) and the forms of cooperation necessary for the success of the travel survey were called into question as a result. From one survey to the next, expansion of the area could mean a jump in the level of project management: from the AOTU to the Conseil Général as in the Alpes-Maritimes in 2009 or even the PACA Conseil Régional over an area that was contained within the departmental boundaries of the Bouches-du-Rhone. There is also a move towards metropolitan scales or strategic planning. New forms of management appeared, which were no longer AOTU, such as "syndicats mixtes" (joint associations of local authorities) that were in charge of SCOTs , 2012). This opening-up corresponded to the proliferation of uses that were made of the surveys.

The use of surveys: between operational objectives and procedural efficiency i. From supplying data for traffic flow models to transport policy indicators

Until the 1980s, what counted was the direct operational purpose of the survey as a source of traffic pattern data.

The SETRA 1975 pilot project dealt summarily with aspects that were secondary to the methodology: a single page of foreword briefly presented the context and objectives of the surveys and the purpose of the brochure and the plan. The guide stated that "the purpose of these surveys no longer needs to be demonstrated" but it explicitly gives only one purpose for household surveys: "The information collected by these surveys is used to create models of traffic production used in transport infrastructure studies" (SETRA, 1975). So there is no need to wonder about the objectives: the model needs the survey and the survey is justified by the needs of the model3 .

The analyses produced at national level at the same period also show this. The series of reports on "characteristics of travel in urban areas" produced by the urban division of SETRA (1975) used the sequential description of 4-step travel models: trip generation, trip distribution and modal choice and route assignment.

The 14 years that elapsed between the "pilot project" (1975) and the first methodological guide by CETUR (1989) reflect the low need for clarification and formalization given that the survey was still running on a "closed loop " basis with technical expertise monopolized by the State. Yet changes were appearing with additional questionnaires, answering concerns specific to the urban area being investigated, but also to the rise of new concerns related to the living environment [START_REF] Cete De Lyon | Les enquêtes ménages. Note 1 : Bilan des enquêtes ménages réalisées depuis[END_REF]. For example, between 1976 and 1983 a questionnaire on mode usage habits emerged. The 1983 report justified this change by moving from "purely economic profitability to "social profitability "", i.e. going beyond a model-oriented goal. The individual was no longer interchangeable: he had become "a user" with "a vested interest".

Opening up to new uses was also influenced by the revival of public transport policies, as illustrated by the setting-up of a Transport Tax (known in French as VT for "Versement Transport") calling on contributions from employers, in the Paris region and then gradually in the provinces since 1973. Besides the number of trips, an indicator appeared to identify the distribution between the different modes. Jean-Marie Guidez, who was then working at CETE Lyon, explained how the term "market share", from the field of marketing, was then preferred to the technical term modal split, at a time when public transport systems were seeking to regain a public [START_REF] Facq | Les fondements statistiques de la science française des déplacements urbains[END_REF].

j. Opening up to local planning

In the late 1990s, the French law on air quality and the rational use of energy (LAURE), introduced in 1996, marked a new turn in making urban transport plans (PDUs) mandatory for urban areas with a population greater than 100,000. But for a decade now, the planning mission of household surveys had already been affirmed. The "methodological guide to household surveys" (1989) adopted a much more aggressive tone on the aims of the surveys and on their quality. From the first pages, the "enquête ménages" label is praised as a guarantor of the methodological rigour, expertise and references of the State services. The argument of the1989 methodological guide was to serve as a reference for the following guides. The wording: "an essential contribution to local planning " and "to knowledge at national level" is still in force today. These two points opened up new fields for the potential uses of household surveys, previously restricted only to traffic patterns. Under the "Local planning" heading, the "household survey reflex" was called on to respond to a wide range of issues: "Road traffic flows for a local public works department; the relations between planning and mobility for an urban planning office; customer data for a public transport network; the aspirations of residents for transport for elected representatives; data on purchasing for a Chamber of Commerce, etc.". In 1998, in the third methodological guide, published this time by CERTU, the aim of urban planning was restated following the LAURE law on air quality and the rational use of energy. The HTS was presented as "an essential tool for drawing up urban travel plans:" "major transport infrastructure in urban areas cannot be planned and urban travel plans cannot be drawn up without reliable and accurate knowledge of the needs of the population, the recent changes it has undergone and its determining factors" (CERTU, 1998).

In recent years, there has been a strengthening of local planning in housing and urban planning as well as in transport organization; which is based on extensive regional diagnostics to draw up scenarios and make commitments through a process of operational actions. Consultations and studies prior to the launch of the PDU allow local elected officials and technical structures to obtain objective and consistent knowledge of the transport system essential for preparing choices [START_REF] Lascoumes | Gouverner par les instruments[END_REF]. Travel surveys are presented as a valuable tool for performing these diagnoses and for fuelling the diagnoses of urban planning or transport documents, and environmental approaches (climate plan, Agenda 21).

A survey on the use of household surveys conducted in 2010 by CERTU with local authorities points to the planning component as the main objective of the surveys. However, an analysis of the respective time frames between conducting the surveys and drawing up the planning documents shows that there is no systematic synchronization, particularly for producing data that might fuel the initial diagnosis [START_REF] Denoyelle | Gouvernance des enquêtes ménages déplacements. Quel rôle pour les EMD dans la coopération entre autorités organisatrices de transport urbain ?[END_REF]. Sometimes the planning process even concludes that it is necessary to launch a travel survey. In the survey conducted by CERTU, a local authority technician explained that study phases are related to mandate cycles, while since the mid-1970s there has been a sort of club of regulars who perform surveys every ten years.

Whether considered as the emergence of a technical project related to the drawing-up of a political project or whether it corresponds to a routine within technical departments that have become "seasoned" in the process, the survey also assumes an increasingly important role in the cooperation between people involved in transport issues.

k. The procedural efficiency of travel surveys at issue

The expansion of boundaries in combination with more diversified uses on the one hand, and the costs of surveys in a context of increasingly tight public budgets on the other are factors which help explain this strengthening of cooperation between the people involved. Travel surveys seem indeed to develop the ability to work together, as evidenced by the development of joint funding by local authorities, while the high level of technical know-how necessary to monitor the collection of data, the CERTU " labelling" process and subsidizing make the State's role an essential one. This increased cooperation can be observed in the development of publications that are increasingly institutionalized. Editorials written by politicians are becoming more frequent, while local partners, more numerous, are more visible on brochures of results, as shown by the more systematic presence of logos: on the covers of publications, there are eight symbols representing the partners of the Nice (2009) and Chambery (2007) surveys, 10 for Saint-Etienne ( 2009) and 21 for Grenoble (2002). Political communication is gradually taking precedence over the technical documents that were highly prized in the seventies and eighties. Today the household survey, a tool to help local authorities communicate about their transport policy, is also an instrument for local marketing, making elected representatives more visible. The first publications were also the basis for the emergence of a common mobility culture between institutions and the general public.

But with its standard dimension, the survey itself is a procedure for generating procedural efficiency alongside its substantive efficiency (modelling and planning), like what Jean-Marc Offner wrote about urban transport plans [START_REF] Offner | L'élaboration des plans de déplacements urbains de la loi sur l'air de 1996 : le nécessaire renouveau des politiques locales de transport[END_REF]. This instrument gives the various local stakeholders time for discussions via the various phases of development: from initial thinking about the relevant area to be surveyed (to be linked to the partners involved, the form that project management will take and the choice of method) to institutional communications and publishing the results for the general public, via the sharing of technical expertise in the production of data (between engineering departments, planning agencies and CETE). The survey period is used to involve local inhabitants in the issue of transport placed on the "political agenda". Wide-ranging communication, accompanied by slogans such as that of the LATS in Calvados ( 2011) "Preparing future transport together", is used to challenge the public so as to associate it with this (new) form of participatory democracy. The survey is legitimate since it allows better decisions to be made while citizens, through their involvement, take part in making "tomorrow's" choices.

In general, what those involved "internally" do when developing the survey, and what those involved "externally" do when disseminating and exploiting the results can be seen as a step towards better cooperation that may be simply informal or more formal. Historically, the new stakeholders such as departmental councils since the 1990s, and regional councils in the 2000s were initially interested in the surveys" on a "pay to see " basis, as the databases were generally issued only to those funding the surveys. Today, the different entities involved seem to share common concerns and tend to pool their objectives more when conducting the survey. They are each then confronted with their own missions and schedules and it is often difficult to keep the collaboration going. Several approaches exist to sustain and expand the partnership beyond the release of the first results. These are usually driven by the existence of a permanent structure such as a partnership travel "observatory", generally hosted and run by an urban planning agency: Marseille (AGAM), Lyon (UrbaLyon), Strasbourg (ADEUS), Rennes (AUDIAR), Montbéliard (ADU), Brest (Adeupa), etc. Their activity is usually stimulated by, or subordinate to, the analysis of data from a travel survey. Some of them even appear to provide support for discussions between institutions on mobility, such as ADEUS's Observatoire Départemental des Déplacements (Departmental Travel Observatory) 4 .

Informal cooperation may give rise to innovative approaches such as the HTS promotion "club" run by the urban planning agency for the Grenoble region. Another example is that of Calvados: as a continuation of work on the survey conducted in 2011 throughout Calvados, "mobility conferences", organized by project management partners (Caen -Métropole, Viacités and the Calvados Conseil général) are proposed. With the aim of " keeping alive travel surveys", the first meeting (in September 2012) looked at multimodality. In the end, this type of initiative is part of a local dynamic that helps appropriate the results of travel surveys and getting them taken into account.

Conclusion

In examining of the role of HTSs in public policy, it has proven very difficult to draw general conclusions. There is no universal law that systematically explains how the tool functions. Unlike the early days of household surveys where the mechanics were well-oiled -the survey fuelled models and its role was not even questioned -HTSs are now much contrasted and multiple in their functions. Confronted with different forms of "giving local accountability back to public action", travel surveys have to push back their boundaries in every sense of the term: from a methodological, spatial, and institutional point of view. They must also be very flexible to use, given the diversity of local needs. In areas of greater contrast (from rural to metropolitan areas), HTSs meet more diverse objectives (planning, analysis of new forms of behaviour, local marketing, local expertise, cooperation between transport authorities, etc.) while maintaining more "conventional" functions (modelling, knowledge / calibration of the offer) that are still acclaimed by the "new customers".

The travel survey can, then, potentially produce "organizational resources" [START_REF] Offner | L'élaboration des plans de déplacements urbains de la loi sur l'air de 1996 : le nécessaire renouveau des politiques locales de transport[END_REF], provided that the dynamics set up when the survey was conducted are extended and amplified. The most successful approaches can be considered as a form of inter-territorial public action, to use Martin Vanier's words (2008). The "household travel survey" instrument is involved in building up local expertise in managing the actual survey, analyzing the results (with the role of research) and also in the empowerment of those involved locally in mobility issues, with the participation of citizens and associations. So it seems that HTSs as we understand the term today are a means of providing procedural efficiency. The survey still produces substantive efficiency as raw material for public policy: not just for programming infrastructure, but potentially for local, environmental and socio-economic planning.

In this movement, the role of the State and its departments is undergoing reconstruction. This role is certainly different, but no less important today: the State is a resource centre, not so much an advisor and producers of technical systems, but more a guarantor of transparency or a disseminator of best practices. The stakes are high, and this is only one step, for while different public policies today have a better shared vision of present reality (through the HTS data), they need to improve their shared vision of the future (particularly through shared transport models).

Fig. 1 .

 1 Fig. 1. Chronology of travel surveys (1975-2013) A growing number of surveys in diverse areas, involving more and more people

Fig. 2 .

 2 Fig. 2. Local coverage of travel surveys in 2013 and type of survey g. Extending the areas: from the urban transport area to the metropolitan areaThe 89 "areas" covered by at least one travel survey are contrasted in terms of population. By 2013, travel surveys conducted outside the Ile-de-France region had covered towns with populations ranging from 40,000 inhabitants (Pompey 2004 ; Dinan 2010 ; Angoulême 2012 ; Pusaye-Forterre 2012, etc.) to 2,000,000 inhabitants(Marseille 2009, Lyon 2006). With the emergence of new methods, two trends can be observed in the spatial dynamics of the surveys. On the one hand, the first surveys were carried out over smaller and smaller areas: the median population of the first surveys before 1999 was 215,000, falling to 140,000 in 2000. On the other hand,

  , of development areas (Bethune and Belfort in 2005, Chambéry and Boulogne in 2007, Calais in 2009 and Amiens in 2010) or of regional studies (SMETD for the French-Geneva border region around Annemasse in 2007). The partnership nature of the control group was also used where "nobody is legitimate" to run the survey alone (Rennes and Rouen in 2007, the Basque-Landes coast around Bayonne in 2010 and the Calvados survey in 2011). The household survey became progressively an "open stage" in the words of Philippe Estèbe to go beyond the preserve of local jurisdictions (CERTU

This term refers to the article by Alain Desrozières "Historiciser l'action publique: l'Etat, le marché et les statistiques -Historicizing public action: State, market and statistics"(2003).

See also the interdependence of the technical matrix described by[START_REF] Commenges | Socio-économie des transports : une lecture conjointe des instruments et des concepts[END_REF].

ADEUS's Observatoire Départemental des Déplacements is an ADEUS permanent partnership structure, responsible for shedding light and providing information on mobility and travel. It conducts studies ranging from the general framework (different geographical scales) to specific analyses (parking, tram network, types of traffic flow, etc.). In addition to the partnership aspect, the observatory conducts discussions with elected representatives on the transport theme, where participants are invited to comment on the data presented.