Eleni Chalkia
email: hchalkia@certh.gr

Maria Teresa De La Cruz

Imre Keseru
email: imre.keseru@vub.be

Alain L'hostis
email: alain.lhostis@ifsttar.fr

Beate Müller
email: beate.mueller@vdivde-it.de

Societal trends influencing mobility and logistics in Europe: a comprehensive analysis

The objective of this paper is to establish a comprehensive view of societal trends that have an impact on mobility and logistics in the future. We have reviewed scientific literature, the output of European research projects and reports from consultancies. The result of this investigation provides a broad and comprehensive set of factors that influence, and will influence in the future, mobility and logistics. The set is composed of 29 trends organised under 9 larger categories covering economic issues, societal issues, urbanisation, the environment, the digital society, new business models, safety, security and the legislative framework.

This work has been strongly inspired by the ideas of the liquid modernity developed by Bauman. This broad and complete view on societal trends has proved to be very supportive of the present analysis. It allows describing linkages between social and economic trends, and between society and technology, especially information and communication technology. Building the analysis on liquid modernity provides coherence and exhaustiveness in covering the topic. The added value of this contribution is its systematic approach and that evidence is provided for each identified trend.

Introduction

Understanding current and future mobility and logistics is a key element in order to shape transport policies and orientate future research. Therefore, establishing a comprehensive view of societal trends that have an impact on mobility and logistics, represents a significant step. In the context of the European research project Mobility4EU1 , such an analysis was carried out [START_REF] L'hostis | MOBILITY4EU -D2[END_REF]. The aim here is to present societal factors, in the broad sense, that influence mobility and logistics. Studying mobility of people and logistics together remains a challenging task. The "last mile" of logistics is very often a matter of individual mobility, which shows how interrelated the two topics can be. Mobility of persons is the most prominent topic in the study of societal trends, but logistics issues can nevertheless be found in several places in our contribution.

There is a broad consensus within scientific literature and in policies that mobility is of crucial importance for society. According to a study by the International Transport Forum in 2011 [START_REF] Wilson | Transport Outlook 2011: Meeting the Needs of 9 Billion People[END_REF]'ITF Transport Outlook 2017' 2017), by 2050 passenger mobility will increase by a staggering 200-300 % and freight activity by as much as 150-250 %.

Mobility is increasingly becoming so important that several authors proposed to replace the study of society by the study of mobility [START_REF] Urry | Mobilities[END_REF]. We chose not to separate society from mobility and transport, but rather to take an integrated approach.

A societal trend is described as an emerging pattern, movement, and evolution in society that leads to change, and potentially has implications for mobility and transport (e.g. ageing, social networks). Societal trends impact transport infrastructure and demand, thus they can be considered key elements for transport related change.

The analysis had to find a compromise between the need to identify and hence separate, and the need to highlight interactions between individual trends and groups of trends. In this perspective trends have been organised in groups of individual trends.

In this work, it has proven difficult to dissociate clearly societal trends from political trends. For example, it is difficult to identify if environmental issues have been led by changes within patterns of behaviour in citizesns or if it has been led by legislation. Likewise, it is difficult to dissociate societal trends from technological trends as expressed in the concept of digital society. Consequently, our analysis of societal trends that impact transport uses five domains of investigation: this analysis covers societal, political, technological, environmental, legal and economic trends.

Another difficulty of the present approach has been to produce a coherent set of trends, shaped around a general view of present and future social behaviour. In order to avoid bias, we chose not to rely only on the sociologists of mobility such as Kaufmann [START_REF] Kaufmann | Re-Thinking Mobility[END_REF], Urry [START_REF] Urry | Mobilities[END_REF] or Kellerman [START_REF] Kellerman | Daily Spatial Mobilities: Physical and Virtual[END_REF], who tend to consider mobility (and immobility) as central societal values. Instead, we refer to a more general view on society, as contained in the idea of liquid modernity introduced by the sociologist Z. Bauman [START_REF] Bauman | Liquid Modernity[END_REF]. This proposal formulates many ideas described in the post-modern concept. This new phase of modernity can be seen as being characterised by five trends:

 a continuing movement of individualism;  the development of fluidity, which can be seen positively with the ideas of change and innovation, but which also has a darker side with respect to the ideas of rupture and precariousness;  the principle of an acceleration of the pace of existence, especially as it is felt through the experience of individuals;  the emergence of social networks that gain more significance, as compared to the more stable and strong [START_REF] Granovetter | The Strength of Weak Ties: A Network Theory Revisited[END_REF]) social ties of the family, or of the workplace;  the introduction of the technologies of information and communication in almost all aspects of social life. One of the merits of this approach is to establish links between domains. Liquid modernity links social dynamics with technology, with social and economic dynamics. In addition, if Bauman [START_REF] Bauman | Liquid Modernity[END_REF] intends to describe society and not mobility itself, building an analysis of mobility out of these elements is very straightforward. Liquid modernity provides a strong support to the list of trends exposed here especially through the linkages it creates between societal trends and between societal and technology trends.

Liquid modernity ideas provide direct insights for understanding persons' mobility, and also gives indications of how freight transport is and should be organised in the future. Needs are more individualised, personalised and hence logistic flow tends to be individual based. Fluidity and the feeling of acceleration converts into the need for immediacy as is reflected in the development of socalled "instant delivery" [START_REF] Dablanc | The Rise of On-Demand "Instant Deliveries" in European Cities[END_REF]). These aspects are devised in the relevant trends.

The emergence of a consensus among social scientists can be observed [START_REF] Clegg | Essai: From Iron Cages to Liquid Modernity in Organization Analysis[END_REF] on the idea of a shift of society towards liquid modernity introduced by [START_REF] Bauman | Liquid Modernity[END_REF]. In consequence, this view provides a sound basis for the analysis of societal trends having an impact on mobility and logistics.

As compared to other similar scientific exercises, this approach is broader and emphasises new trends. Several researchers have focused on trends in favour of sustainable transport [START_REF] Rudinger | Societal Trends, Mobility Behaviour and Sustainable Transport in Europe and North America: The European Union Network S LA'. ℡LA[END_REF][START_REF] Boschmann | Toward Socially Sustainable Urban Transportation: Progress and Potentials[END_REF], while others have studied trends from travel surveys in a single country [START_REF] Frändberg | More or Less Travel: Personal Mobility Trends in the Swedish Population Focusing Gender and Cohort[END_REF]. As compared to other similar exercises in European research, our approach is rooted in the study of societal trends as opposed to a more classic transport demand analysis, found in for example TransForum [START_REF] Anderton | Asylum Statistics -Statistics Explained[END_REF], TRANSvisions [START_REF] Petersen | TRANSvisions Final Report on Transport Scenarios with a 20 and 40 Year Horizon[END_REF], FUTRE [START_REF] Bernardino | FUTRE Deliverable 3.1: Factors of Evolution of Demand and Pathways[END_REF], RACE2050 (Sena e Silva et al. 2013), EUTransportGHG [START_REF] Sessa | EUTransportGHG Report EU Transport Demand: Trends and Drivers[END_REF], ORIGAMI [START_REF] Lemmerer | ORIGAMI Deliverable 3.1 Current Travel Behaviour, Future Trends and Their Likely Impact[END_REF] and VOYAGER [START_REF] Brög | Societal Megatrends: Like It or Not, the Framework Is Set[END_REF]. These approaches tend to separate trends along classic transport modes and transport markets, without extending into the study of societal trends. As opposed to these approaches, firstly we analysed societal dynamics in a broad sense, and secondly identified trends that have an interaction with mobility and logistics. In this work, societal trends are starting points instead of more traditionally starting with the identification of transport solutions or markets. This approach complements previous research. In addition, as opposed to more thematic approaches to studying societal trends, for instance CITYLAB on freight [START_REF] Dablanc | CITYLAB Observatory of Strategic Developments Impacting Urban Logistics (2016 Version)'. Deliverable 2-1 CITYLAB European Project[END_REF] or TransForum on several targeted transport sectors [START_REF] Anderton | Asylum Statistics -Statistics Explained[END_REF], our analysis intends to cover all transport modes, all geographical scales and freight as well as passenger transport.

Method

The objective of this chapter is to establish a comprehensive view of societal trends that impact mobility and logistics. In this aim, a literature review has been conducted, encompassing published scientific sources, research reports and statistics sources.

In order to set up a comprehensive view, a list of trends has been created. A set of rules has been defined for the identification of these trends in relation to mobility and logistics. Firstly, a trend is coherent, not equivocal. A trend can carry a paradox, like the trend about the acceleration of liquid modernity, and a trend can also move in a single direction.

Secondly, a trend is not redundant. Bearing in mind the complex nature of societal issues, the task of building a set with little overlap has proved challenging.

Thirdly, the set of trends should not omit factors or tendencies in society in the broad sense that may exert an influence on mobility and logistics.

And finally, a trend must be described and supported by evidence found in the literature. Statistics, surveys, and figures are provided for each trend. These analytical elements determine the direction of the influence exerted on mobility and logistics. In cases where an idea was formulated without evidence, it was not considered as a trend.

Societal, political, technological, environmental, legal and economic trends interacting with mobility and logistics

We are developing an analysis of this system of trends in the present with a temporal horizon of 2030. Consequently, the description of trends aims at capturing the present situation and the dynamics of these trends in the future.

The result of this process is the following list. This list can be seen as the shortest possible set of trends that allows describing present and emerging societal factors, in a broad sense, that have an impact on mobility, both for freight and passengers' mobility.

The list is composed of 29 trends organised under 9 larger categories. These larger categories cover economic issues, societal issues, urbanisation, the environment, digital society, new business models, safety, security and finally, the legislative framework. Table 1 lists the categories and the trends, and indicates the type of each trend: social, political, economic, technological and legal. Considering that trends can be of several types, it can be observed that 16 trends are social, 8 trends are economic, 6 trends are political, 4 are technological, 4 are legal, and only one is environmental. If, as expected, more than half of the trends refer directly to social issues, the other aspects play a significant role in the description of trends.

The next section describes the trend categories in detail.2

3.1 Economic trends Economic climate and economic conditions play a major role in shaping the demand for mobility. In the economic domain two trends have been identified. Firstly, it is foreseen that the adaptation of Europe's economy in the global context will have a relative decline of GDP [START_REF] Bassanini | Financial Stability, Fiscal Consolidation and Long-Term Investment after the Crisis[END_REF]. European GDP and population should grow but much slower than the rest of the world on average. The direct consequence of global growth will be an increase in flows, particularly freight, but also the possibility of a re-industrialisation of Europe, which could lead to significantly modified freight flows ('ITF Transport Outlook 2017' 2017). At the individual level, economic growth usually converts into more mobility, as illustrated by the growth of tourism.

The second trend within this category refers to the restructuring of working arrangements. Telework and part-time work are the two major foreseeable tendencies already at work and that should grow in the future [START_REF] Isusi | Part-Time Work in Europe[END_REF][START_REF] Jagger | Raising the Retirement Age: Implications for UK and Europe[END_REF]. They have direct and indirect effects on mobility. Although there is a decreasing quantity of home-to-work flows, they could take longer due to the urban sprawl made easier by telework and less peak hour traffic, as there may be more trips for other purposes [START_REF] Jackson | Productivity and Work in the "Green Economy": Some Theoretical Reflections and Empirical Tests[END_REF][START_REF] Bernardino | FUTRE Deliverable 3.1: Factors of Evolution of Demand and Pathways[END_REF]. A likely consequence of the last effect has been identified as a demand for more flexible tickets for public transport.

Societal trends

The second category of trend refers to societal dynamics that interact with mobility and freight demand. Most of these trends are mainly societal dynamics such as; "Increasing life expectancy of the population" or "Migration trend generating long distance flows", but some of them are also supported by "Move towards more active and healthy lifestyles" or driven by "Trend towards inclusion of vulnerable to exclusion groups" and "European integration facilitating flows".

"Increasing life expectancy of the population" is an essential dynamic of European societies (Eurostat 2015; World Health Organization and The World Bank 2011). The interaction with mobility and logistics are complex though: the population of car drivers is likely to grow, and less active mobility is expected from the "oldest old", but maybe more active mobility will come from those who will stay or move back to denser urban areas; a need for proximity in goods and service deliveries for the urban elders contrasts with specific and costly mobility demand in ageing rural areas [START_REF] Anderton | Asylum Statistics -Statistics Explained[END_REF][START_REF] Velaga | Transport Poverty Meets the Digital Divide: Accessibility and Connectivity in Rural Communities[END_REF].

"Migration trend generating long distance flows" (European Commission 2011) introduces or develops specific patterns of mobility demand: the foreseen increasing migration in Europe will generate longer distance flows of persons and goods with the countries of origin of migrants ('Asylum Statistics -Statistics Explained' 2016;[START_REF] Vasileva | Citizens of European Countries Account for the Majority of the Foreign Population in EU-27 in 2008 -Issue Number 94/2009 -Product -Eurostat[END_REF].

There is a consensus on the fact that policies support a "Trend towards inclusion of vulnerable to exclusion groups" [START_REF] Martens | Justice in Transport as Justice in Accessibility: Applying Walzer's 'Spheres of Justice'to the Transport Sector[END_REF]. This trend has a direct impact on transport policy in terms of accessibility for all. In addition to known vulnerable groups, the digitisation of mobility carries the risk of creating new exclusion, for instance among those who do not own a smartphone [START_REF] Pauzié | DECOMOBIL Deliverable 3.4 Nomadic Transport Services for Multimodal Mobility: Issues and Perspectives[END_REF][START_REF] Velaga | Transport Poverty Meets the Digital Divide: Accessibility and Connectivity in Rural Communities[END_REF].

Forming part of the explanation of the peak car phenomenon, the tendency of "Less car usage by younger generations" has been observed recently since the mid-2000 [START_REF] Davis | Transportation and the New Generation: Why Young People Are Driving Less and What It Means for Transportation Policy[END_REF][START_REF] Goodwin | Three Views on Peak Car[END_REF][START_REF] Newman | Peak Car Use and the Rise of Global Rail: Why This Is Happening and What It Means for Large and Small Cities[END_REF][START_REF] Metz | Peak Car and beyond: The Fourth Era of Travel[END_REF]. Connecting to the social network, whatever the means, physically based or telecommunication based, seems to have replaced the car ownership dream observed in previous generations [START_REF] Deloitte | The Future of Mobility, How Transportation Technology and Social Trends Are Creating a New Business Ecosystem[END_REF][START_REF] Mckinsey | Decisions to Reduce Greenhouse Gases from Agriculture and Product Transport: LCA Case Study of Organic and Conventional Wheat[END_REF].

Another consequence of the societal awareness for environmental issues is the "Move towards more active and healthy lifestyles". This trend is fuelled by individual awareness and by policies aimed at influencing individual behaviour. Health is likely to become a major concern in the future with direct implications for the policies aimed at orientating mobility behaviour [START_REF] Krzyzanowski | related+air+pollution&ots=O65x2DGs9z&sig=5IKuTQngcA2[END_REF].

There is an emerging consensus among social scientists around the idea of liquid modernity introduced by Z. Bauman [START_REF] Bauman | Liquid Modernity[END_REF]. In order to characterise the interactions of liquid modernity with mobility and logistics two trends have been established: "Acceleration and flexibility of liquid modern society" and "Personalisation of liquid modern society". The first trend refers to the ideas of acceleration and flexibility and provides an explanation to the increase of leisure time and its associated mobility patterns [START_REF] Harvey | The Condition of Postmodernity: An Enquiry into the Conditions of Cultural Change[END_REF][START_REF] Levine | A Geography Of Time: The Temporal Misadventures of a Social Psychologist[END_REF][START_REF] Rosa | Social Acceleration: Ethical and Political Consequences of a Desynchronized High-Speed Society[END_REF]. It also entails that transport users need less time for planning their trips, and have access to immediate and seamless information. The second trend of liquid modernity highlights the personalisation aspect. The individualisation process, illustrated among other indicators by the decreasing size of households (Euromonitor 2013; [START_REF] Capros | EU Energy, Transport and GHG Emissions: Trends to 2050, Reference Scenario[END_REF], favours individual transport modes of cars but also bike and walking, and also favours models of the type "one-stopshop" for mobility services.

Essentially driven by policies and political choices "European integration facilitating flows" is still, despite the recent reverse movement by the United Kingdom, an ongoing process. Its impacts on mobility are straightforward through the increase in tourism and freight flows in Europe [START_REF] Kester | 2013 International Tourism Results and Prospects for 2014[END_REF].

Urbanisation

Urbanisation is the major trend of human settlement. Despite an already high level of urbanisation in Europe, it is foreseen that urbanisation is set to increase from 73 % in 2014 to 84 % in 2050 (United Nations 2014).

Cities and city-regions, which are densifying and spatially extending, are increasingly the dominant forms of settlement [START_REF] Fujita | The Spatial Economy: Cities, Regions, and International Trade[END_REF]. These trends lead to more intense and longer urban flows, both for passengers and goods (Sena e Silva et al. 2013).

The emerging model of the smart city aims at articulating human and social development with information and communication technologies in cities (European Investment Bank Institute EIB 2013). Equipping cities with ICT infrastructure is being led by the introduction of new technologies of mobility (mainly electric vehicles, car sharing, car-pooling) and should lead to new social interactions and to new uses of city spaces, and hence should have significant impact on mobility behaviour and freight demand.

Environmental protection

In the domain of environmental protection, four trends can be identified. The first three are led or encouraged by policies, while the last one refers to the management of the consequences of climate change.

Rising awareness for environmental issues leads to the adoption of "Stricter regulations for environmental protection". Transport has a large impact on the environment, and is confronted with the strategic policy goals of decarbonisation [START_REF] Pachauri | Fifth Assessment Report -Synthesis Report Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change[END_REF][START_REF] Anderton | Asylum Statistics -Statistics Explained[END_REF].

The economy is adapting in the context of increasingly limited resources available ("Limited resources require more resource efficiency and circular economy in transport"). A "sustainable consumption" culture emerges among citizens and firms tend to conform to social and environmental rules and approaches: corporate responsibility, circular economy, life cycle assessment [START_REF] Petersen | TRANSvisions Final Report on Transport Scenarios with a 20 and 40 Year Horizon[END_REF]. All these elements will require the reconsideration of the organisation of logistics, as for instance in the case of local food consumption that need short supply chains [START_REF] Blanke | Food (Miles) for Thought-Energy Balance for Locally-Grown versus Imported Apple Fruit (3 Pp)[END_REF][START_REF] Coley | Local Food, Food Miles and Carbon Emissions: A Comparison of Farm Shop and Mass Distribution Approaches[END_REF][START_REF] Mckinsey | Decisions to Reduce Greenhouse Gases from Agriculture and Product Transport: LCA Case Study of Organic and Conventional Wheat[END_REF][START_REF] Kulak | Life Cycle Assessment of Bread from Several Alternative Food Networks in Europe[END_REF][START_REF] Dablanc | CITYLAB Observatory of Strategic Developments Impacting Urban Logistics (2016 Version)'. Deliverable 2-1 CITYLAB European Project[END_REF]).

In the domain of energy, policy goals support a movement to "Move away from fossil fuels towards energy efficiency and renewable energies" (European Commission 2011;[START_REF] Harrison | Fuelling Europe's Future[END_REF]. The current dependence of transport on fossil fuels is expected to be replaced by more electricity and biofuels [START_REF] Pachauri | Fifth Assessment Report -Synthesis Report Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change[END_REF].

Finally, regarding environmental trends, the "Impact of climate change on transport" is direct and significant. Extreme weather events cause damages to transport systems of road, rail and aviation [START_REF] Doll | Large and Small Numbers: Options for Quantifying the Costs of Extremes on Transport Now and in 40 Years[END_REF]. Global warming could have one positive effect though, to open the North-West passage for freight between Europe and Asia [START_REF] Anderton | Asylum Statistics -Statistics Explained[END_REF].

Digital society and the Internet of things

In this section on digital society, two types of trends are covered. Regarding the digital world, technology, as an enabler, exerts a real influence and drives individual and social uses. Two technological trends of "Internet of things and big data", and "automation" form the supply side. But at the same time, technology is sometimes used for a slightly different purpose than what was foreseen by the designers. In this sense, individuals and social groups can be seen as actors of digital society, and able to fuel trends that are not driven by technology. This is the demand side of digital society.

The technological trends of "Rise of the Internet of Things and big data" is impacting many aspects of the production of goods and services, and particularly in the transport domains. Vehicles, transport infrastructures, ICT devices, parcels will all be able to communicate in real-time. Dealing with the masses of data produced require new methods, the so called big data approaches, but promise to improve many transport issues like transport operations planning, traffic management, or safety [START_REF] Löffler | The Internet of Things and the Future of Manufacturing | McKinsey & Company[END_REF][START_REF] Jeske | Big Data in Logistics: A DHL Perspective on How to Move beyond the Hype[END_REF][START_REF] Zakir | Big Data Analytics[END_REF].

The trend of "More automation" is driven by the development of artificial intelligence, sensors and information and communication technologies [START_REF] Frisoni | Research for TRAN Committee -Self-Piloted Cars: The Future of Road Trans-port?[END_REF]. This technological development has ambitious road safety promises, but also raises difficulties expressed in another trend ("The emerging safety issue in complex networks with new vehicles"). Automation is also developing in the air and rail transport domains [START_REF] Verstraeten | OPTICS 2nd Expert Workshop: From Hazard Management to Operational Resilience[END_REF].

Regarding the demand side of the digital society, the first trend refers to the "Expectation of customers and digitisation of mobility". Travellers in the digital world expect to be able to connect their mobile devices, and expect to receive accurate and real-time information about their trips [START_REF] Pauzié | DECOMOBIL Deliverable 3.4 Nomadic Transport Services for Multimodal Mobility: Issues and Perspectives[END_REF]. All these expectations are challenging for transport providers [START_REF] Deloitte | Transport in the Digital Age, Disruptive Trends for Smart Mobility[END_REF]. Quite ambivalently, travellers also want more data privacy [START_REF] Pauzié | DECOMOBIL Deliverable 3.4 Nomadic Transport Services for Multimodal Mobility: Issues and Perspectives[END_REF] Mostly driven by the development of the digital society, "New uses of traveltime" can be observed [START_REF] Jain | The Gift of Travel Time[END_REF][START_REF] Lyons | Comparing Rail Passengers' Travel Time Use in Great Britain between 2004 and 2010[END_REF]. Usually seen as a burden, travel time can become a positive moment for users. This trend is able to influence the transport mode choice in favour of public transport [START_REF] Russell | Travel Time Use on Public Transport: What Passengers Do and How It Affects Their Wellbeing[END_REF]), until automation is introduced.

Novel Business models in transport

The transport sector witnesses the emergence of new players and new business models interacting with -if not fuelled by -new behaviour. New business models are closely related to the previously mentioned trend of "Rise of the Internet of Things and big data". The main issue is the currently dominating individual vehicle ownership model, described in the first trend "New models challenging the individual vehicle ownership model" [START_REF] Shaheen | Personal Vehicle Sharing Services in North America[END_REF][START_REF] Hardesty | Ride-Sharing Could Cut Cabs' Road Time by 30 Percent[END_REF][START_REF] Cirstea | The Implications of Mobile Commerce Applications: The Case Study of Uber in Romania[END_REF]. The second trend covers the other cases where new players and new business models emerge, in batteries, in data, in freight "New players and new business models" [START_REF] Forbes | Tesla's Business Model Highlights What The Shift To Electric Means For The Auto Industry[END_REF][START_REF] Leminen | Ecosystem Business Models for the Internet of Things[END_REF][START_REF] Rantasila | Development of ITS Multi-Service from Idea to Deployment[END_REF][START_REF] Casey | Towards an Open Ecosystem Model for Smart Mobility Services[END_REF]. The last trend highlights the emergence of the co-development model and its implications for mobility: "Emerging co-development and co-creation of new systems by users and economic actors"(Chang and Yen 2012; Finnish Prime Minister's Office 2015; [START_REF] Kostiainen | Public Transport ITS Test Environment for a Smart City[END_REF] .

Safety in transport

Despite significant improvement of the levels of safety, especially in the road transport domain, and encouraging perspectives linked to automation, transport safety will most probably remain a pressing issue in the future ('European Commission Press Release -2015 Road Safety Statistics: What Is behind the Figures? ' 2015).

Considering the long-term promise of the decrease in road casualty through the introduction of automated cars, a new safety issue emerges with the coexistence of automatic and non-automatic vehicles, creating complex networks and environments [START_REF] Lazakis | EXCROSS Final Report on Synergies and Opportunities[END_REF]. Safety will become a far more complex issue than today with new insurance and liability issues [START_REF] Smith | Automated and Autonomous Driving: Regulation under Uncertainty[END_REF].

Security in transport

Terrorism is a growing concern in our societies and for governments [START_REF] Zellner | Threat Perceptions in the OSCE Area[END_REF]. Attacks often target transportation infrastructure, and hence the interaction between this trend and mobility and freight is straightforward [START_REF] Jenkins | The Terrorist Threat to Surface Transportation[END_REF]). More security is expected which raises the security and accessibility tension: the provision of more security in transport by introducing controls and barriers reduces accessibility.

3.9

Legislative framework

The legislative dimension converts societal demand, through the production of laws and rules by public authorities and jurisprudence. This legislative dimension is an expression of the broader policy process and institutional environment that directly affects the transport sector. Nevertheless, beyond the mere role of translation of societal demand, the legislative dimension can be considered as a dynamic on its own, and hence can be considered as a societal trend in the broad sense. Three legislative trends exert influence in the domains of mobility and logistics.

We observe in the legislative domain a trend of "Diversifying approaches of governance" (European Environment Agency 2015). More actors are invited to contribute to the governance of transport and mobility. In particular, with the association of citizens in decision processes, more transparency is required in governance models [START_REF] Albrechts | More of the Same Is Not Enough! How Could Strategic Spatial Planning Be Instrumental in Dealing with the Challenges Ahead?[END_REF]. The innovation at play in the domain of legislation and governance, leads to a diversification of governance models.

Secondly, with the trend "Legislative models adapting to new transport solutions and businesses" an interaction occurs between new business models and the legislative framework. The legislative framework has to adapt to new solutions [START_REF] Azevedo | Social, Economic and Legal Consequences of Uber and Similar Transportation Network Companies (TNCs) -Think Tank[END_REF], but newcomers must also make sure their business can sustain in a given and changing legislative framework.

The "Trend toward harmonisation in legislative frameworks" of the legislative framework in Europe has direct implications for transport, in the aims of interoperability of transport systems ('Road Transport: Harmonisation of Legislation | EU Fact Sheets | European Parliament' 2016). This trend refers also to the fact that legislative adaptations to new models and solutions in a given European country will inspire other countries' reactions.

Interrelations between trends

In this section we present the main interrelations between these trends. Even though this work mostly identified and isolate individual factors interacting with mobility and logistics in an unequivocal sense, the intrinsically interdependent nature of our material cannot be ignored.

The main interactions between trends form three groups. A small group links societal dynamics to policies aimed at correcting or accompanying them. A large group includes all the links between societal trends and digital technologies. Finally, a few remaining interrelations are identified beyond these two categories.

The first group of interrelations links policies, expressing the will of policy makers, and societal trends as actual transformations in the social field. Several emerging trends in transport demand are pushed by policies, but can also be seen as reflecting societal demand. This is the case in the environmental protection domain where a sustainable consumption culture interacts with extensive sets of policies dedicated to environment protection. Hence, the present analysis mixes societal trends, like ageing, and political responses to identified issues like policies aiming at inclusion of vulnerable groups.

The second group of interrelations links society and digital technologies. The liquid modern society described by Bauman [START_REF] Bauman | Liquid Modernity[END_REF], is intimately shaped by digital technologies of information and communication. There is hence clearly a strong link between the two trends of liquid modernity and the four trends of the digital society. The current and future digital society would not exist without the technology developments in communication and information, but, on the other hand, the use by individuals and social groups is not always envisaged by the creators of services, yet contribute significantly to shaping the digital society. In this sense, digital society is shaped by technology and by societal factors. As is well known in the domain of transport infrastructure, a new supply generates a demand that was not expressed before: this is the so called induced demand. Digital society is rooted in the societal trends of liquid modernity, and also influences the transport demand. The expectation of the customer having a specific dynamic in the digital world. And the digital society does not limit to transport user requirement, but has deep interactions with mobility in general, including avoiding mobility.

The observed reduction in car use by younger generations has been seen by several analysts as linked to a change in values. The possession of a car tends to be replaced by the idea of connecting to the social network; this points to the use of ICT and hence to several trends identified in the digital society section.

A trend towards the inclusion of vulnerable groups can be identified. But in the emerging digital society new forms of exclusion arise; these forms are particularly of concern in the transport and mobility sectors. Here a clear issue lies at the intersection of public policies aiming at inclusion and the development of new transport services making use of ICT.

We have identified a trend of new uses of travel time, mainly by means of ICT that currently favours public transport. But, in the future car automation is likely to erase this comparative advantage. A complex interaction of trends exists here, with evolving developments over time.

Beyond the two categories of interrelations, three other linkages can be identified.

Complex interactions link automation and transport safety. Automation comes with the promise of significant improvement of the levels of safety in transport, but it also introduces new kinds of safety problems; an illustration is the selfdriven Tesla car casualty accident in 2016 and the many similar events since then. This represents a new type of accident raising significant liability and insurance issues most likely to impact the legislative and regulatory frameworks.

The responses to the security threat perception, as noted, carries the risk of introducing more controls that may be detrimental to the ease of access and use of collective transport systems. The trend of a security versus accessibility tension is clearly contrary to the fluidity, acceleration and flexibility features of the liquid modern society.

Liquid modernity is both a consequence, or a symptom, and a source for the observed restructuring working arrangements. Indeed, the observation of acceleration is paradoxically based on the growing mobility for non-work purposes, and hence directly related to the idea of growing part-time work described in the restructuring arrangement trend. This forms an example of the links between economy and society.

This review of linkages was necessary to reveal the complexity of the system of trends. This review also contributes to validating the list of trends, by distinguishing many factors for the understanding of the present and future dynamics between society and transport.

Conclusion

This paper focuses on the identification and description of societal trends shaping the demand of mobility and logistics. The work has led to the identification of a list of 29 societal trends covering societal trends, political, economic, technological and legal trends. The result of this investigation forms a broad and comprehensive set of factors that influence, and will influence future, mobility and logistics. This approach has been organised so that, even if trends are linked one to another, as can be seen in the last section, no duplication can be found in the set of trends. This set borrows characteristics of a system in the sense that individual sub-parts, once assembled, form a coherent set.

This work has been strongly inspired by the ideas of the liquid modernity developed by Bauman. Liquid modernity highlights key societal trends of individualism, of the fluidity of society, of the feeling of acceleration of the pace of life, of the growing importance of social networks, and of the role of information and communication technologies. This broad and complete view on societal trends has proved to be very supportive of the present analysis. It allows to describe linkages between social and economic trends, and between society and technology, especially information and communication technology. Basing the analysis on liquid modernity provides coherence and exhaustiveness in covering the topic.

The added value of this contribution is its systematic approach and that evidence is provided for each identified trend. The proposal forms a broad and comprehensive view of societal trends that play, and will play, a role in shaping the demand for mobility and logistics in Europe at the horizon 2030. The trends identified in this paper form the bases of the scenario building in the Mobility4EU project which is the subject of the paper "Building scenarios for the future of transport in Europe: The Mobility4EU approach" in Chapter X.

Table 1 : The 29 societal trends having an impact on mobility and logistics and their categories

 1

	Categories	Trends	Type of trend
	3.1 Economic	Share of the European economy in world GDP	Economic
	trends	declines
		Restructuring working arrangements	Economic, Social
	3.2 Societal trends Increasing life expectancy of the population	Social
		Migration trend generating long distance flows	Social
		Trend towards inclusion of vulnerable to exclusion	Political
		groups
		Less car usage by younger generations	Social
		Move towards more active and healthy lifestyles	Social
		Acceleration and flexibility of liquid modern society Social
		Personalisation of liquid modern society	Social
		European integration facilitating flows	Political
	3.3 Urbanisation Rising and expanding urbanisation	Economic, Social
		The emergence of Smart cities	Technological
	3.4 Environmental	Stricter regulations for environmental protection	Social, Political
	protection	Limited resources require more resource efficiency	Economic, Social
		and circular economy in transport
		Move away from fossil fuels towards energy	Political,
		efficiency and renewable energies	Economic,
			Technological
		Impact of climate change on transport	Environmental
	3.5 Digital society	Rise of the Internet of Things and big data	Technological
	and the Internet of	More automation	Technological
	things	Expectation of customers and digitisation of	Social
		mobility
		New uses of travel-time	Social
	3.6 Novel Business	New models challenging the individual vehicle	Economic, Social
	models in transport	ownership model
		New players and new business models	Economic
		Emerging co-development and co-creation of new	Economic
		systems by users and economic actors
	3.7 Safety in	The persisting issue of transport safety	Social, Political
	transport	The emerging safety issue in complex networks with	Social, Legal
		new vehicles
	3.8 Security in	Growing concern over security threats	Social
	transport

The Mobility4EU project aims at producing a roadmap for mobility and logistics

in 2030 starting from societal needs. The overall objective consists in linking present and future societal trends and needs to existing and emerging transport and mobility solutions. http://www.mobility4eu.eu

For a detailed description of trends see[START_REF] L'hostis | MOBILITY4EU -D2[END_REF]).

Acknowledgements

The authors thank, Corinne Blanquart, Freek Bos, Annette Brückner, Thierry Coosemans, Laetitia Dablanc, Erzsébet Földesi, Alessia Golfetti, Stefania Grosso, George Holley-Moore, Juho Kostiainen, Jochen Langheim, Gereon Meyer, Linda Napoletano, Cristina Pou, Annette Randhahn, Joachim Skoogberg, Yves Stans, Anu Tuominen, Marcia Urban, Susana Val, Ineke van der Werf for their inputs in this work.

The authors thank Amna Diaz from ILC for language check. The authors wish to thank the European Commission for the funding of the MOBILITY4EU project in the framework of the Horizon2020 program (EC Contract No. 690732).


Antonio Mauttone
email: mauttone@fing.edu.uy

Martine Labbé
email: mlabbe@ulb.ac.be

Rosa M V Figueiredo

A Tabu Search approach to solve a network

Keywords: Network design, shortest path routing, discrete bilevel programming, tabu search

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The fixed charge network design problem (FCNDP) consist of selecting a subset of edges from a graph, in such a way that a number of given commodities can be transported from their origins to their destinations. The problem states the minimization of the sum of fixed costs (due to selecting the edges) and variable costs (depending on the flows of commodities on those edges). Both fixed and variable costs are linear and the edges are uncapacitated. The FCNDP problem is a large class of network design problems [START_REF] Magnanti | Network design and transportation planning: Models and algorithms[END_REF].

A variant of the FCNDP states that the commodities are routed along a shortest path on the resulting network. We call this problem FCNDP-SPR. This characteristic adds new constraints to the general problem.

Namely, consider a network G = (V, E) where V is the set of vertices and E is the set of admissible edges linking these vertices. A length, a fixed and a variable cost are associated with each edge in the graph. Consider also, a set K of commodities to be transported along the edges in E. Each commodity k ∈ K is associated with an origin-destination pair of vertices (o k , d k ). The FCNDP-SPR problem is to select a set of edges in E to be opened and to find, for each commodity in K, a feasible flow in the resulting network such that the sum of the fixed costs plus the variable flow costs is minimized. For a commodity k ∈ K, a flow is said to be feasible if it is sent along a shortest path from o k to d k , with respect to the edge lengths.

The FCNDP-SPR involves two distinct decision makers acting non-cooperatively and in a sequential way. At the upper level the leader is in charge of choosing the set of edges to be opened and he makes this decision trying to minimize the fixed and variable costs. As an answer, at the lower level the followers choose a set of shortest paths in the resulting network along which the commodities will be sent. The effect of a decision maker on the other part is indirect: the followers' decision is affected by the network designed in the upper level whereas the leader's decision is affected by the variable costs imposed by the routes set in the lower level.

The inclusion of shortest path routing constraints in a mixed integer program is not straightforward. Difficulties arise both at the modeling as well as to design efficient solution methods. For the best of our knowledge, the FCNDP-SPR has only been addressed two times in the literature [START_REF] Billheimer | Network design with fixed and variable cost elements[END_REF][START_REF] Kara | Designing a road network for hazardous materials transportation[END_REF] and has been treated as part of bigger problems in some applications [START_REF] Holmberg | Optimization of internet protocol network design and routing[END_REF].

The remainder of this text is structured as follows. In Section (2) we present a discrete bilevel formulation [START_REF] Colson | Bilevel programming: A survey, 4OR: A Quarterly[END_REF] and a one-level integer formulation to the FCNDP-SPR problem. In Section (3) a tabu search procedure for the FCNDP-SPR problem is briefly described. Preliminar computational results for the one-level formulation and the tabu search are provided in Section (4). Finally, in Section (5) some concluding remarks are given.

Discrete formulations

Let A E = {(i, j), (j, i) | ∀ [i, j] ∈ E} be the set of arcs obtained by bidirecting the edges in E. With each edge e ∈ E we associate a fixed opening cost f e and with each arc a ∈ A E we associate a positive length c a and an operating variable cost g k a , for each commodity k ∈ K. Considering an arc a = (i, j) ∈ A E we define e(a) = [i, j] and ā = (j, i). Also, considering an edge e = [i, j] ∈ E we define a(e) = (i, j) and ā(e) = (j, i). Notice that there is no capacities associated neither with edges in set E nor with arcs in set A E .

Each commodity k ∈ K must be sent along one unique path carrying the total demand associated with its origin-destination pair. Then, for each commodity k ∈ K a demand vector b k ∈ {-1, 0, 1} |V | is specified as

b k i =    1 if i = o k , -1 if i = d k , 0 otherwise.
For each edge e ∈ E, we define an upper level variable y e ∈ [0, 1] such that y e = 1 if and only if edge e is part of the network design. Also, for each commodity k ∈ K we define a set of continuous lower level variables x k a , a ∈ A E , used to model the shortest path from vertex o k to vertex d k , with respect to the lengths c a . The discrete bilevel formulation (BIP) to the FCNDP-SPR problem is

min y e∈E f e y e + k∈K a∈A E g k a x k a (1)
y e ∈ {0, 1}, ∀ e ∈ E, (2)
where x is a solution to the problem

min x k∈K a∈A E c a x k a (3) subject to a∈δ + (i) x k a - a∈δ -(i) x k a = b k i , ∀i ∈ V, ∀k ∈ K, (4)
x k a(e) + x k ā(e) ≤ y e , ∀ e ∈ E, ∀k ∈ K, (5)
x k a ≥ 0, ∀a ∈ A E , ∀k ∈ K. (6) Let δ + (i) (respectively δ -(i))
denotes the set of arcs having node i as its tail (respectively head).

The upper level objective function (1) minimizes the sum of the fixed and variable costs. The lower level problem is described by ( 3)-( 6) in which constraints (4) are the well-known flow conservation constraints. Constraints (5) force each variable y e(a) to take value 1 whenever x k a is positive for some k ∈ K.

The FCNDP-SPR problem can be reformulated as a one-level integer formulation by replacing the lower-level linear program defined by ( 3), ( 4), ( 5) and ( 6) with its optimality conditions. That could be done by applying the fundamental theorem of duality and the complementary slackness theorem [START_REF] Bazaraa | Linear Programming and Network Flows[END_REF]. However, optimality conditions for the lower level problem are, in fact, shortest path optimality conditions and they can be written in a more compact and effective way considering the Bellman optimality conditions for the shortest path problem [START_REF] Ahuja | Network flows[END_REF] and using a simple lifting procedure [START_REF] De Giovanni | The internet protocol network design problem with reliability and routing constraints[END_REF].

A one-level formulation (IP) for the FCNDP-SPR problem is as follows. 4), ( 5),

min y,x e∈E f e y e + k∈K a∈A E g k a x k a subject to (2), (
x k a ∈ {0, 1}, ∀a ∈ A E , ∀k ∈ K, (7) π k i -π k j ≤ M k -y e(a) (M k -c a ) -2c a x k ā, ∀a = (i, j) ∈ A E , ∀k ∈ K, (8)
π k d k = 0, ∀k ∈ K. (9) Variables π k i , k ∈ K, i ∈ V
, are the shortest distances from vertice i to vertex d k . Then, we can set variable π k d k equal to zero. Assuming the integrality of variables y and x and assuming also that inequalities (5) are satisfied, constraints (8) are equivalent to Bellman optimality conditions for the set of |K| origin-destination pairs. The constant value M k , k ∈ K, has to be sufficiently large to guarantee that variables π k i and π k j will satisfy the shortest path conditions whenever y e = 0, e = [i, j] ∈ E.

A simple tabu search procedure

Tabu Search (TS) is a metaheuristic originally proposed by Glover [START_REF] Glover | Tabu search part I[END_REF] to allow local search methods to overcome local optima. Its basic principle is to accept non-improving moves in order to allow the local search to escape from local optima; cycling back to already visited solutions is prevented by using memories called tabu lists, that record the recent history of the search [START_REF] Gendrau | An introduction to tabu search[END_REF]. TS has been successful in solving many hard combinatorial optimization problems, obtaining approximate solutions that are close to optimality [START_REF] Glover | Tabu search[END_REF].

In this work we apply TS to obtain approximate solutions to the FCNDP-SPR problem. Our main interest at this stage of the work is to compare its performance against the bounds obtained using the (IP) formulation in a branch-and-bound framework, for problem instances of different sizes. We propose a TS based on the algorithm of Wen and Huang [START_REF] Wen | A simple tabu search method to solve the mixed-integer linear bilevel programming problem[END_REF], that is originally proposed to solve mixed-integer linear bilevel problems with discrete variables in the upper level. The algorithm of Wen and Huang represents a solution by recording explicitly the value of each variable of the higher level of the mathematical formulation. Our algorithm, that we call as Simple Tabu Search (STS), uses the same solution representation; thus we are able to use information coming from the mathematical formulation to improve the performance of STS.

STS represents a solution S as a binary vector (s 1 , . . . , s |E| ), where s e = 1 means that edge e belongs to S (s e = 0 if e is not included in S). We use the neighborhood structure proposed by Wen and Huang, where the set N (S) of neighbor solutions of S is obtained by replacing s e by 1s e for each e ∈ 1..|E|. This simple neighborhood structure changes the status of an edge in the solution, including the edge if it is not included or removing it, if it is included on the solution; according to this, the size of N (S) is |E| for any solution S. Notice that the search only changes values of the y variables of the formulation (those belonging to the higher level); the values of x variables must be calculated according to the lower level problem, which in our case is equivalent to calculate |K| independent shortest paths.

Algorithm 1 shows a pseudo-code of STS. At line 3, a new solution is constructed by following a given procedure; it must check that the solution allows to connect the origin and destination vertices of each commodity (constraint (4)). The neighborhood of S i is explored at line 5. For each neighbor obtained by changing the status of a single edge, the feasibility of the resulting network G is checked with respect to constraint (4). Then, shortest paths in G are calculated for every commodity k. Since formulation (BIP) implicitly represents the optimistic version of the bilevel problem [START_REF] Colson | Bilevel programming: A survey, 4OR: A Quarterly[END_REF], we must check the existence of more than one shortest path for each commodity. If q k is the number of shortest paths from o k to d k in G , we evaluate the objective function of the higher level for q 1 × . . . × q |K| different solutions of the x variables and we select the less costly according to objective function (1). At line 6, the tabu list is updated, by stating thatthe edge involved in the move performed at line 5, can not change its value during the following t local search iterations (where the value of t is set according to a given criterion). The tabu status of a move can be dropped (aspiration) if the move leads to a solution with less cost than a given value (aspiration level). STS was tested using a set of random instances specially generated for this problem. The instances are characterized by three parameters, namely number of vertices n, number of commodities k and density of edges α ∈ [0, 1]. The program that generates the instances takes these parameters, and randomly generates m (a fourth parameter) different instances with the characteristic indicated by (n,k,α). Parameter α is used as a probability to decide whether or not to include in the instance, each possible edge of the complete undirected graph of n vertices. Fixed and variable costs, and edge lengths are set as random uniform numbers in the integer range [1..100].

Instances were generated for values of n in the set {10, 20, 30}; for each value of n we considered values of k in {n/2, n, 3n/2} and α in {0.3, 0.5, 0.8}. For each one of these 27 combinations of parameters, we generated m = 5 different instances.

We solved the formulation (IP) using the Branch and Bound algorithm of the Xpress Optimizer 1.7, turning off its pre-solve routine and its automatic cuts generation. We put a time limit of 1 hour in a 1 GHz processor computer.

The solver found the optimal solution for the small and medium-sized instances. For the smallest instances (10 vertices), it took less than 1 second. For some of the biggest instances (30 vertices, density 0.8, 30 and 45 commodities), the solver does not found the optimal solution within the imposed time-out.

For the TS we configured the algorithm as follows: the number of startingSolutions is equal to |E|, t is randomly selected at each move from the integer interval 1..|E|, the stopping criterion uses a time limit and a condition that is true when no improvement is found after |E|/2 moves. The aspiration level is set as the objective value of the current solution of the search. The algorithm was coded in C++, and run in a 1.8 Ghz computer. The time limit was 30 minutes. We implemented three variants of the routine of generation of initial solutions:

1. Uniform random generation (STS1): for each edge e, a random uniform value in the real interval [0, 1] is sampled, and it is used to decide whether or not to include the edge on the solution.

2. Biased random generation (STS2): similar to the previous one, but using probabilities which are proportional to the value of the variable y e , in the optimal solution of the linear relaxation of (IP) formulation.

3. Profit-guided generation (STS3): the edges are sorted in decreasing order according to the values of their respective variables in the optimal solution of the linear relaxation of (IP) formulation. At each new solution generated, a new edge is added to it taken from the sorted list described above.

Table 1 shows the results produced by both exact (Branch and Bound) and approximated (STS) approaches, for the 5 instances of characteristic (30,30,0.8). In that table, z best and z * are the objective value of the best solution found by the exact and approximated approach respectively, t is the CPU time in seconds and gap = (z bestz * )/z best * 100 is the percentage gap. We observe that gap values of STS1 are very high ( †), while gaps of STS2 and STS3 are much lower ( ‡). This suggest that the information provided by the optimal solution of the linear relaxation of formulation (IP) greatly improves the performance of the STS algorithm; on the other hand the "blind" generation of solutions of STS1 performs poorly when compared with the exact approach. Moreover we observe that the exact approach does not found the optimal solution for 4 out of the 5 instances (-), while STS2 and STS3 found better solutions for 3 of these instances ( ).

Conclusions and future work

A variant of the fixed charge network design problem is studied, where the commodities are routed along the shortest path of the network. We model it as a linear mixed-integer bilevel problem with discrete variables in the upper level, and we solve it using a tabu search algorithm. We compare the results of the tabu search against exact solutions obtained by branch and bound using a one-level integer linear formulation derived from the original bilevel formulation. Tabu search obtains good results, specially for the biggest instances of the problem; information coming from the linear relaxation of the one-level integer formulation greatly contributes to the performance of the tabu search.

Some aspects of the implementation of the tabu search could be changed in order to improve its performance. The computation of shortest paths during the exploration of the neighborhood is a critical component of the overall algorithm. Avoiding recomputation of all these paths [START_REF] Buriol | Speeding up dynamic shortest-path algorithms[END_REF] could improve the performance of the algorithm.

Table 1 :

 1 Results for instances(30,30,0.8)

		Exact			STS1			STS2			STS3
	instance z opt	t	z *	gap	t	z *	gap	t	z *	gap	t
	1	4830 61,39 52119	979,07 † 1802 5026 4,06 ‡	230 4927 2,01 ‡ 1110
	2	7276	-	50788	598,02 † 1810 7426 2,06 ‡ 1262 7322 0,63 ‡	93
	3	8749	-	58623	570,05 † 1826 8321		98 8142		565
	4	9741	-	64783	565,05 † 1822 8864		1059 8828		1287
	5	7560	-	83644 1006,40 † 1870 7573 0,17 ‡ 1212 7502		794

Acknowledgments: This work was supported by grant from Coordenac ¸ão de Aperfeic ¸oamento de Pessoal de Nível Superior-CAPES and the Project ALFA II-0457-FA-FCD-FI-FC.