Explaining Trends in Car Use Anne Bastian Doctoral Thesis KTH Royal

Explaining Trends in Car Use

Anne Bastian

Doctoral Thesis

KTH Royal Institute of Technology

School of Architecture and the Built Environment

Department of Transport Science

Stockholm, Sweden 2017

TRITA-TSC-PHD 17-003

ISBN 978-91-88537-01-0

Avhandling som med tillstånd av Kungliga Tekniska Högskolan framlägges till offentlig granskning för avläggande av teknologie doktorsexamen fredagen den 13 oktober 2017, klockan 10 i Kollegiesalen, Kungliga Tekniska Högskolan, Stockholm.

Abstract

Many western countries have seen a plateau and subsequent decline in car travel during the early 21st century. What has generated particular interest and debate is the claim that the development cannot only be explained by changes in traditional explanatory factors such as GDP, fuel prices and land-use. Instead, it has been argued, the observed trends are indications of substantial changes in lifestyles, preferences and attitudes to car travel and thus, not just a temporary plateau but a true peak in car use.

This thesis is a compilation of five papers, studying the issue on a national, international, regional and city scale through quantitative analysis of aggregate administrative data and individual travel survey data. It concludes that the aggregate development of car travel per capita can be explained fairly well with the traditional model variables GDP and fuel price. Furthermore, this thesis shows that spatial context and policy become increasingly important in car use trends: car use diverges over time between city, suburban and rural residents of Sweden and other European countries, while gender and to some extent income become less differentiating for car use.

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Sammanfattning

Många länder i västvärlden har sett en platå och efterföljande nedgång av bilresandet under det tidiga 2000-talet. Vad som har genererat särskilt intresse och debatt är uttalandet att utvecklingen kan inte bara förklaras genom traditionella förklaringsfaktorer som BNP, oljepriser och markanvändning. I stället har det hävdats att de observerade trenderna är indikationer på betydande förändringar i livsstil, preferenser och attityder till bilresandet; alltså inte bara en tillfällig platå utan en verklig topp i bilanvändning.

Denna avhandling är en sammanställning av fem artiklar som studerar fenomenet på nationell, internationell, regional och storstads nivå genom kvantitativ analys av offentlig aggregerad statistik och individuella resvaneundersökningar. Slutsatsen är att den samlade utvecklingen av bilresor per capita kan förklaras ganska väl med de traditionella modellvariablerna BNP och bränslepris. Vidare visar avhandlingen att geografiskt sammanhang och fysisk planering blir allt viktigare för bilanvändnings trender: Bilanvändningen skiljer sig åt över tid mellan stad, förort och landsbygd i Sverige och andra europeiska länder, medan kön och i viss mån inkomster blir mindre särskiljande för bilanvändning.

Acknowledgements

I am grateful to my supervisor Maria Börjesson for her guidance, consistent support, trust and encouragement. Maria was always open to discussing ideas, and she inspired me with her passion for transport and society. I am fortunate and grateful to Maria Börjesson and Jonas Eliasson for the opportunity to join the Centre for Transport Studies. Jonas Eliasson and Oded Cats co-supervised parts of my work, and they supported me by sharing their experience, encouragement and good advice. Lars-Göran Mattsson, Margareta Friman, and Yusak Susilo provided valuable comments as my seminar opponents. I would like to thank my friends and colleagues at the Centre for Transport Studies, and Stef Prost for their countless acts of support and inspiring conversations. Furthermore, I am grateful to the Department of City and Regional Planning at UC Berkeley for hosting my stay. I have also received help and data from Transport Analysis Sweden, the City of Stockholm, Stockholm County’s public transport administration, Statistics Sweden, and Transport for London. My studies were financed by the Centre for Transport Studies in Stockholm.

List of papers

I Bastian, Anne, and Börjesson, Maria. 2015. “Peak Car? Drivers of the Recent Decline in Swedish Car Use.” Transport Policy 42 (August): 94–102.

II Bastian, Anne, Börjesson, Maria, and Eliasson, Jonas. 2016. “Explaining ‘Peak Car’ with Economic Variables.” Transportation Research Part A: Policy and Practice 88 (June): 236–50.

III Bastian, Anne, Börjesson, Maria, and Eliasson, Jonas. 2017. “Response to Wadud and Baierl: ‘Explaining “Peak Car” with Economic Variables: An Observation.’” Transportation Research Part A: Policy and Practice 95 (January): 386–89.

IV Bastian, Anne, and Börjesson, Maria. 2015. “Peak Car for Urban Swedish Men?” Presented at the 14th International Conference on Travel Behaviour Research, Windsor, July, 2015.

V Bastian, Anne, and Börjesson, Maria. 2017. “The city as a driver of new mobility patterns, cycling and gender equality: Travel behaviour trends in Stockholm 1985-2015.” To be submitted.

Contributors

For papers I, IV and V: Anne Bastian and Maria Börjesson jointly developed the respective research questions and edited the papers to their final version. Anne Bastian was responsible for gathering relevant data, analysis and writing.

For paper II: Anne Bastian, Maria Börjesson and Jonas Eliasson jointly developed the respective research questions and edited the paper to its final version. Anne Bastian was responsible for gathering relevant data, analysis and writing.

For paper III: Anne Bastian, Maria Börjesson and Jonas Eliasson jointly developed the content and edited the paper to its final version. Jonas Eliasson was responsible for writing. Anne Bastian was responsible for analysis.

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1 Introduction 1.1 Background Many western countries have seen a plateau and subsequent decline in car distances driven per capita during the early 21st century. Some countries and regions have even seen a decline in the absolute distances travelled by car. What has generated particular interest and debate is the claim that the development cannot only be explained by changes in traditional explanatory factors such as GDP, fuel prices and land-use, and that these traditional factors have not been pivotal to the development of car distances travelled per capita. Instead, it has been argued, the observed trends are indications of substantial changes in lifestyles, preferences and attitudes to car travel and thus, not just a temporary plateau but a true peak in car use (Puentes and Tomer 2008; Millard-Ball and Schipper 2011; Goodwin 2012; Metz 2013; Goodwin and Dender 2013; Goodwin 2013).

This thesis is a compilation of five papers, studying the issue on a national, international, regional and city scale through quantitative analysis of aggregate administrative data and individual travel survey data. The work towards this thesis began in 2013, shortly after Goodwin (2012) at the International Transport Forum roundtable on the issue, summarized the state of research as follows:

“There are currently differences in judgement on how influential these factors are, and on whether the observed trends are temporary, or reflect structural shifts which could be long-lived. These differences especially focus on the relative importance of economic issues (particularly prices and incomes), and wider social and cultural changes such as mobile internet access, demographic, gender, attitudinal and cultural trends, the effects of transport policies, and the possibilities of deeper concepts of ‘saturation’ of mobility when further increases bring little extra benefit. There is at the moment no strongly established common view about future growth in car use to the extent that was taken for granted in earlier decades.”

Furthermore, Goodwin (2012) describes a lack of synthesis between the analysis of aggregate trends at national level and the experience of cities and other places. He suggests that individual travel survey data can provide a bridge. This thesis aims to build such a bridge, by analysing both aggregate statistics and individual travel survey data in Sweden and reconciling the observations.

Millard-Ball and Schipper (2011) introduce the term peak car. The term is then adopted by much of the following literature about the 1

“observation of slower rates of growth, levelling off, or reduction, in various measures of car use, which have been seen in many though not all developed countries” (Goodwin and Dender 2013). In this thesis the primary measure of car use is VKT (vehicle kilometres travelled by car) per capita.

Much of the argument for the importance of changes in attitudes to explain the recent VKT trends, is built on the statement that the plateaus in car use preceded the economic crisis and peak in oil prices and therefore should not be attributed to them (Goodwin 2012). This thesis challenges the peak oil timing argument. By re-examining the role of fuel prices on aggregate VKT trends, this thesis proposes an answer to what Stokes (2013) called the greatest unknown in the peak car debate: “the uncertainty over why peak car appears to be occurring in so many countries”.

The peak oil timing argument can be traced back to Puentes and Tomer (2008), who discuss United States vehicle kilometre trends in the context of monthly real gasoline price and oil price data. They notice an increasing monthly volatility in gasoline prices since 2006 and focus on the 2008 price peak moment. However, they dismiss a 35% increase in real gasoline prices from 2000 to 2005 as ‘‘relatively stable”. This leads them to conclude: ‘‘Thus, only the most recent drop in per capita driving is coupled with gasoline price spikes”. Their focus on oil price trends – which have more extreme peaks than gasoline prices – may also have focused their attention on the 2008 peak in the oil price, giving less attention to the increase in gasoline price in the preceding years. The peak oil pricing argument is cited and adapted without any own modelling by influential papers that shaped the peak car debate (Millard- Ball and Schipper 2011; Metz 2010, 2013; Newman and Kenworthy 2011; Goodwin 2012). Millard-Ball and Schipper (2011) cite Puentes and Tomer’s argument and conclude that the traditional economic variables, GDP and fuel price, ‘‘can only provide a partial explanation” of the car use trend. They do not analyse alternative explanations, but note that travel demand theory suggests a saturation point for car travel, analogous to a saturation point for vehicle ownership (Tanner 1978): when every driver has a car, there is no need for more cars. They position their paper as a ‘‘challenge to travel demand and energy models that project continued rises in VKT and passenger travel”.

Goodwin (2012) points out an important drawback of modelling long- term national VKT trends based on only GDP per capita and fuel prices: simplistic models assume that VKT growth is linear in population growth. Yet, one would expect a less than proportional growth in VKT when national population growth occurs primarily in cities, as opposed 2

to rural areas, due to differences in travellers’ destination and mode alternatives. Goodwin (2012) therefore classifies urbanization and the resulting non-linearity of VKT growth in national population growth as a weakness of modelling VKT based on only GDP and fuel price trends. Indeed, there is much literature on the fact that elasticities differ substantially between individuals depending on the availability of mode and destination alternatives (Blow and Crawford, 1997; Santos and Catchesides, 2005; Wadud et al. 2009, 2010). This thesis investigates the increasing divide of car use and related travel behaviour between city, suburban and rural populations in Sweden, and how urbanization and other changes in the population’s spatial distribution and composition affect VKT per capita trends. However, I do not adopt the degree of Godwin’s (2012) concern for the explanatory power of traditional transport modelling in the peak car context. First, more advanced transport models that are used in practice do consider the location of population and employment growth, for example the Swedish national transport model. Second, while the location of future population growth is important for long-term trends in travel behaviour, the change occurs slowly and can only explain a small share of the national average VKT per capita changes during the 2000 decade in England (Headicar 2013) and Sweden (as this thesis will show).

Furthermore, this thesis calls in question the dichotomy of economic factors versus other explanatory factors, which was suggested by some peak car literature and which Goodwin (2012) called the economic versus the alternative school of thought. This thesis does not rule out changes in attitudes and lifestyles (alternative school of thought). Instead, it suggests that there is no need to assume that attitude changes are exogenous to economic factors, in order to explain the changes in VKT per capita. I argue that attitude changes to a large extent follow economic incentives, since many long-term lifestyle trends appear to be driven by economic incentives. A recent analysis of Millennials’ activity and travel patterns found that their delay in life milestones compared to previous generations - such as finishing education, getting jobs and having children - and the related travel behaviour appear to be driven to a large extent by economic conditions (Garikapati et al. 2016). Much research has shown that attitudes are correlated with travel behaviour; however, the causality appears to be bidirectional (Tardiff 1977), and there is some evidence that individuals are more likely to adjust their attitudes to match their travel behaviour than vice versa (Kroesen, Handy, and Chorus 2017; Tardiff 1977). Therefore, this thesis argues that changes in attitudes may to a large extent be the consequence or parallel outcome, rather than the cause, of changes in car use.

Aggregate VKT per capita trends mask significant variation in different population groups, locations, and trip purposes. This thesis also explores the importance of disaggregate trends that were pointed out in the peak car literature and how they might apply to Sweden: a trend decline in younger people holding driving licenses (Delbosc and Currie 2013; Kuhnimhof et al. 2012); company car taxation and access (Le Vine et al. 2013); travel demand saturation (Metz 2010; Newman and Kenworthy 2011; Grimal, Collet, and Madre 2013; Goodwin 2012); a shift away from car use in urban areas (Goodwin 2012; Metz 2015; Headicar 2013; Le Vine and Jones 2012); and ICT use affecting the attractiveness of city versus suburban locations (van Wee 2015; Lyons 2015). The thesis also investigates trends that point towards increasing car use: seniors relying more on cars (Kuhnimhof et al. 2013), and more long-distance travel (Frändberg and Vilhelmson 2011; Millard-Ball and Schipper 2011).

1.2 Motivation The planning and prioritization of transport infrastructure and transport policy relies to a large extent on forecasts of future growth in VKT. Road and parking infrastructure is costly, has major and lasting impacts on its surroundings, and it can require decades of advance planning and negotiation. Understanding drivers of national VKT trends is important for developing national climate and environmental policies, fiscal planning, and the planning within related industries. Understanding how VKT trends differ between different spatial contexts and socio-economic groups is important for defining local and regional policies (that aim for example to affect road congestion, air quality, accessibility, and social equity), and for planning and prioritizing land-use policy and infrastructure investments.

Forecasts of the future largely rely on understanding the factors that have led to past changes. Transport forecasting models rely on the assumption that the parameters explaining past travel behaviour remain constant over time (Fox and Hess 2010). These parameters typically capture responses to changes in economic, demographic and land-use variables, such as GDP, fuel price, geographical distribution of firms and population by socio-economic status. If the main drivers of car travel are changing, then forecasting models and transport policies need to adjust to this change.

This thesis studies Sweden as a country, and Stockholm County as a metropolitan area, and it explores the extent to which the findings are applicable to similar high-income countries and metropolitan areas. Sweden is among the countries in which Millard-Ball and Schipper (2011) first noted a reduced growth of VKT during the 2000 decade.

Sweden, and Stockholm in particular, are interesting case studies because they are world leading in societal trends, such as gender equality, new uses of ICT, the shift towards a digital and knowledge economy, and towards environmentally sustainable cities. Furthermore, Sweden offers comparatively detailed and reliable data: a series of cross- sectional national travel surveys starting in 1978, a series of cross- sectional travel surveys of Stockholm County starting in 1984, and a municipality-level time series of annual VKT (collected from mandatory car inspections) starting in 2012.

2 Research questions This thesis investigates the drivers of changes in VKT per capita since the 2000 decade in Sweden and other high-income countries. The aim is to contribute to the understanding of which factors had a pivotal effect and which might gain importance in the future. There are four main research questions.

Question 1: Has the traditional transport modelling approach, relying on GDP per capita and fuel prices, lost predictive power? Is it still sufficient to explain aggregate VKT trends?

Question 1 was prompted by noticing a lack of quantitative modelling in the peak car literature, which argued that traditional economic transport models can only provide a partial or secondary explanation for the reduced growth in national VKT in the 2000 decade (Puentes and Tomer 2008; Newman and Kenworthy 2011; Goodwin 2011; Millard-Ball and Schipper 2011; Metz 2013). (OECD/ITF 2013) is the first paper that tries to quantify the explanatory power of GDP and fuel price in the peak car context, using aggregate time series data from 1980 through 2007 for a number of countries. The crucial difference between their models and the models in this thesis is that the authors assume that elasticities are equal across countries. Since there are substantial differences in fuel prices, car ownership and average driving distances between countries, I argue that it is natural to assume that elasticities with respect to real GDP per capita and real fuel prices will also vary between countries. This is indeed confirmed by the large literature studying these elasticities.

Paper I addresses this gap in the literature by analysing aggregate Swedish statistics. The results of paper I, however, do not take into account the fact that car use has developed very differently in different socio-economic groups. For instance, Grimal et al. (2013) find signs of saturation of car use in the highest income segment in France. Kuhnimhof et al. (2011; 2013) find that among young adults, in particular among men, car use plateaued already in the 1990s and

decreased after the turn of the millennium in the UK and Germany. This heterogeneity is addressed via research question 3 in papers IV and V.

Paper II explores the extent to which the findings from paper I can be generalized to six high-income countries: the United States, the United Kingdom, France, Sweden, Australia and Germany. All countries but Germany are chosen for three reasons: they represent interesting examples of industrialized countries with a pronounced trend break in VKT since the 2000 decade, there is data available, and the countries have experienced no other major exogenous changes or events that affect VKT, with the exception of changes in the United Kingdom company car regulations. The countries are also different in many respects: car mode shares and average trip distances vary significantly between them, as do transport policy and fuel taxes. Paper III discussed the methodology of paper II in more detail.

The approach of paper II is to explore to what extent fuel prices and GDP per capita, and these variables only, are able to explain the observed VKT per capita trends. If one can refute the default hypothesis that the aggregate trends in VKT can be explained by fuel price and GDP, the observed development must indeed be caused by something else. This could be other ‘‘hard” (measurable) variables such as urbanization, parking, congestion or vehicle taxation, which are explored in Paper IV and V. But if even such variables are not enough to explain the observed trends, it would be strong support for the more exciting hypothesis that we see effects of exogenous changes in ‘‘soft” (difficult to measure) variables such as lifestyles, attitudes and preferences.

Papers I and V also address how VKT per capita trends vary between city, suburban and lower density areas. This is in response to the literature suggesting that elasticities are higher (in absolute terms) in urban than rural areas (J. M. Dargay 2002; Wadud, Graham, and Noland 2010), and the peak car literature suggesting that recent reductions in VKT per capita occurred mostly or more strongly among urban populations (Goodwin and Dender 2013).

Question 2: To what extent do changes in the spatial distribution and socio-economic composition of the population contribute to the VKT per capita trends?

Question 2 was brought about by the literature arguing for the importance of the spatial distribution of future population growth and changes in the socio-economic population composition (Goodwin 2012; Goodwin and Dender 2013; Headicar 2013). This thesis analyses the effects on VKT of: urbanization, ageing, foreign immigration, spatial

population sorting and growth, and changes in the level and distribution of incomes and education levels.

Paper I analyses to what extent the differences in population growth between different Swedish municipalities, for example due to urbanization, have contributed to reduced growth in national Swedish VKT per capita. A similar analysis by Headicar (2013) for the United Kingdom concluded that, in the perspective of a few years, urbanization had a small effect on national VKT per capita.

Paper IV analyses the extent to which changes in the socio-economic composition of the Swedish population have contributed to changes in car use. This captures, for example, the increasing education and income levels among older women. A limitation of Paper IV is that it does not differentiate residential locations within metropolitan regions, due to limited sample sizes. Paper V addresses this limitation by using a larger survey dataset of Stockholm County, which allows for the important distinction between inner city, regional centre, inner suburban, and outer suburban areas. Controlling for residential location in paper V allows us, for example, to determine the extent to which reductions in driving among high income groups are due to them becoming more likely to live in central city locations.

Question 3: How do trends in car use in Sweden vary across socio- economic groups?

Question 3 aims to complement the findings on aggregate car travel. The aggregate statistics used in papers I, II and III are more reliable than travel survey data for studying changes over time, but they are less useful in addressing heterogeneity in travel behaviour across different socio-economic groups and spatial contexts. Question 3 focuses explicitly on personal travel, as it is captured in travel surveys, while question 1 was concerned with the aggregate trends of personal and commercial car travel. Thus, this thesis does not analyse disaggregate trends in commercial car use, due to limitations in both data availability and the scope of the thesis.

The peak car literature observes large variations in VKT trends by gender, age group, residential location and income (Kuhnimhof, Buehler, and Dargay 2011; Kuhnimhof, Zumkeller, and Chlond 2013; Grimal, Collet, and Madre 2013; Metz 2015). Studies of Australia, Germany and the United Kingdom point out a substantial reduction in young adults’, and particularly young men’s, licence holding, car ownership and VKT (Delbosc and Currie 2013; Kuhnimhof, Zumkeller, and Chlond 2013). In Sweden, Frändberg and Vilhelmson (2011) noted that women upwardly

adjust their travel distances, resulting in a smaller gender gap in overall mobility. Paper IV adds to this literature by differentiating between trends in metropolitan versus other areas of Sweden, controlling for socio-demographic variables, and by focusing on trends in everyday car use. Paper V analyses how men and women in different locations within Stockholm County have adjusted their travel behaviour over time.

Grimal et al. (2013) observe signs of saturation in car use among high income population segments in France. In Sweden, since the 2000 decade real income gains have occurred to a large extent in higher income groups and higher age groups, suggesting that average income increases may have had a smaller effect on car use than previously. Paper I analyses how VKT elasticities differ between Swedish municipalities by mean income, controlling for population density and public transit supply. Paper IV analyses the cross-sectional relationship of income and VKT, and the trends in VKT per capita in different income segments of the Swedish population. Paper IV also attempts to consider changes in fuel prices along with socio-demographic and spatial variables, though the trends in fuel prices cannot fully be distinguished from unobserved factors that also evolved gradually over time. Paper V analyses the extent to which income effects of car use interact with residential location choices within Stockholm County. Goodwin and Dender (2013) argue that high income groups moving to more central locations may partly explain why the income effect on car use appears to be decreasing among high income groups.

Question 4: What are the travel behaviour trends in the inner city, suburbs and remote areas of Stockholm County? How are these travel behaviour trends related to societal changes, such as increasing gender equality, new uses of ICT, and the transition to a knowledge economy?

Question 4 addresses a missing link between the travel behaviour studies in the peak car literature and the studies of agglomeration effects in the urban economics literature. Most studies of trends in car use consider individual’s socio-economic and spatial context and incentives; few consider trends in housing costs (Delbosc and Currie 2013), and to my knowledge none comprehensively consider the effects of urban agglomeration (via real estate prices, population sorting, congestion, and changing activity locations). When comparing reports by the transport authorities of Stockholm, London, Copenhagen, and the Netherlands, I noticed several common trends in travel behaviour in these metropolitan regions and a common divergence of travel behaviour between their central, suburban and remote areas. I hypothesized that these commonalities are related, not only to common transport and land-use 8

policy trends, but also to the fact that these regions attract highly skilled knowledge economy workers and companies, and consumers of services and entertainment. What is more, Stockholm is world leading in the societal trends towards increasing gender equality, and adapting new uses of ICT. Paper V relates these societal trends to changes in travel behaviour, land-use, and population sorting in Stockholm County. Many societal trends occur simultaneously and are interconnected, and there are no counterfactual examples of comparable cities that have not experienced these trends. Therefore, paper V describes hypotheses about how societal trends likely affect land-use, the location of housing, jobs and activities, and it relates this to the observed changes in travel behaviour in Stockholm and other European capital cities.

Table 1 summarizes the relationships between the four main research questions and the five papers in this thesis.

Table 1

Paper Paper Paper Paper Paper I II III IV V Transport modelling: a loss of Q1 x x x predictive power? Structural: location of growth Q2 and composition of x x x population Heterogeneity: trends by Q3 socio-economic group and x x x location City pull forces: societal vs. Q4 travel behaviour trends in x Stockholm County

3 Contributions This section outlines how the papers in this thesis contribute to the academic and policy literature.

Question 1: Has the traditional transport modelling approach, relying on GDP per capita and fuel prices, lost predictive power? Is it still sufficient to explain aggregate VKT trends?

Papers I and II are the first papers in the peak car context to allow for elasticities to vary by country, and this modification leads to different conclusions than (OECD/ITF 2013). The results provide reassurance to transport modelling. Transport modelling is based on the assumption

that preferences stay constant over time, given economic factors, land- use and socio-economic characteristics.

Paper I shows that the two variables GDP per capita and fuel price can explain most of the aggregate trends in VKT per adult in Sweden. The estimated elasticities are well in line with previous literature and can reasonably well reproduce the trend in VKT per adult back to 1980. The fact that VKT per capita has even decreased in rural areas of Sweden, though to a smaller degree than in cities, during periods of rapidly rising fuel prices suggests that indeed fuel prices are an important driver of VKT trends. The results of paper I show, however, a substantial spatial variation in elasticities between municipalities, depending on agglomeration size, public transport supply, population density, share of foreign-born inhabitants and the average income level. This heterogeneity is further investigated in papers IV and V.

Papers I, II and III challenge the dichotomy of economic factors versus other explanatory factors, which was implied by some prior literature and which Goodwin (2012) called the economic versus the alternative school of thought. Paper I shows that most of the observed changes in Swedish VKT per capita can be explained by GDP and fuel prices (economic school of thought) and that the composition and location of population moderate VKT growth. The moderating effect of population location is considered in advanced transport models, for example the Swedish national transport model, but Goodwin (2012) categorizes this as belonging to the alternative school of thought. Papers I, II and III do not rule out changes in attitudes and lifestyles (alternative school of thought). Instead, I suggest that there is no need to assume that attitude changes are exogenous. Attitude changes may to a large extent follow economic incentives, since many long-term lifestyle trends, such as urbanization and more young people acquiring university education, appear to be driven by economic incentives. Much research has shown that attitudes are correlated with behaviour; however the causality is bidirectional, and there is some evidence that individuals are more likely to adjust their attitudes to match their travel behaviour than vice versa (Kroesen, Handy, and Chorus 2017).

Paper II analyses the extent to which the main finding of paper I can be extended to other high income countries. It shows that GDP and fuel price are sufficient to explain the aggregate trends in car use in the United States, France, the United Kingdom, Sweden, and to a large extent Australia. Paper II presents an argument against the conclusion - by much of the prior literature - that peak oil prices occurred too late to explain the changes in car use from 2004. I argue that the importance of the fuel price increases in the early 2000s has been underappreciated in 10

the studies that shaped this debate. This would also explain why the levelling off in VKT occurred in so many countries at a similar point in time. Furthermore, paper II results corroborate prior literature in that GDP elasticities tend to decrease with rising GDP. This appears to be a slow and long-term process that has been occurring over many decades.

Paper II finds that fuel price elasticities (in absolute terms) tend to increase at high fuel price levels and during periods of rapid price increases. These findings corroborate earlier literature studying elasticities, but this had not been considered in the context of peak car models. Literature prior to the peak car debate showed that gasoline price elasticity seems to depend on the fuel price level (Goodwin, Dargay, and Hanly 2004), and that responses to sudden large fuel price increases are not perfectly reversible (J. Dargay and Gately 1997).

Paper III discusses the methodology of paper II in more detail, in particular the theoretical versus practical benefits of estimating the elasticities on time series of different lengths. It demonstrates that elasticity estimates can be strongly influenced by including a particular event in the time series, such as a sudden price jump, even if the event occurs in only one out of 20 years of data.

Question 2: To what extent do changes in the spatial distribution and socio-economic composition of the population contribute to the VKT per capita trends?

Papers I and IV find that changes in the location and composition of the Swedish population have contributed to changes in VKT per capita, but that this is a slow process and thus not the main driver of the comparatively rapid changes in VKT per capita since the 2000 decade.

Paper I corroborates a rather counterintuitive finding by Headicar (2013): that the direct effect of urbanization, viewed at a municipality level, is not a large driver of the changes in national VKT per capita during the 2000 decade. However, urbanization could be more important when considering a longer time horizon and when considering possible spatial aggregation trends within municipalities. Paper I also discusses the impact of foreign immigration to urban regions in Sweden on VKT per capita trends, to the extent that the limited data availability allows.

Paper IV investigates the impact of changes in the socio-demographic composition of the population on VKT per capita. It shows that population ageing, during the 1990 and 2000 decades did not have a large net impact on the changes in VKT per capita in Sweden, though this may change when large cohorts retire. The observed gradual increases in car use among older non-urban women can largely be explained by 11

increases in income and education. Yet, the observed strong decreases in VKT per capita among men, and urban men in particular, cannot be explained by structural change. These changes might be a response to rising fuel prices and unobserved factors. I argue that urban men are the group with the best opportunities to adjust: they have a high absolute level of car use, they tend to have good access to alternative modes and destinations, and a large share of their driving is for non-commute purposes. One limitation of the analysis in paper IV is that there are only two spatial categories: urban and non-urban residents of Sweden. This is addressed in paper V, in which the large sample size of the Stockholm County surveys allows for further spatial disaggregation.

Paper V argues that population sorting and growth within Stockholm County has contributed to decreases in the car share of trips and in the average length of car trips in Stockholm County between 2004 and 2015. Socio-economic groups who tend to make more and longer trips ( working-age, high-income, single) have concentrated more in the regional centre, while those who tend to make fewer trips (retirees, low- income, couples) have increased primarily in the suburbs.

Question 3: How do trends in car use in Sweden vary across socio- economic groups?

This thesis finds evidence consistent with saturation in car use among the highest income segments, by analysing data at individual, municipality and country level. It finds that income is becoming less differentiating for car use, as average incomes rise and income increases mainly accrue to higher income groups. I argue that high income population segments tend to have good opportunities to reduce their driving for several reasons: they drive more than other income groups, a large share of their driving is not for commuting, in Stockholm and similar metropolitan areas they increasingly live and work in areas with good access to alternative modes and destinations. However, results in paper II suggest that saturation of car use is a slow process and not the main driver of the comparatively rapid changes in national VKT per capita during the 2000 decade. A counterforce to saturation of car use among high income populations in Sweden is company cars, which are disproportionally supplied to high income and male drivers, and their use is very inelastic to pricing. Le Vine et al. (2013) find that reduced company car access explains some reductions in driving among British men, but this is not the case in Sweden.

Paper IV finds that urban men of all income groups considerably reduced their driving between 2006 and 2011, for any trip purpose but most strongly for leisure trips. This could indicate that increasing urban

congestion, parking limitations and time constraints played a role, or that high income men became more likely to reside in central urban locations. Both of these hypotheses are addressed in Paper V.

Paper V finds that some of the reductions in driving among high income urban adults are due to population sorting, high income individuals thus becoming more likely to reside in the regional centre as opposed to suburban areas. Yet, even after controlling for residential location, I find that VKT per capita has decreased among all income groups of Stockholm County from 2004 to 2015. Car use decreased most for trips to or from the inner city and among high-income men living in the outer suburbs (which is also the group with the highest absolute VKT level and the group who increased their transit use the most). Further, I show that commercially owned cars make up an increasing share of VKT in Stockholm County.

The results of papers IV and V corroborate prior literature in that gender is becoming less differentiating for car use over time, though there remains a substantial gender gap in all measures of car use that cannot be explained by socio-economic controls. Frändberg and Vilhelmson (2011) find that at the national level in Sweden, women’s travel distances follow an increasing trend, becoming more similar to men’s travel distances. In other European countries reduced car use among men was found to be the main reason for smaller gender gaps in car use (Kuhnimhof et al. 2012). Paper IV reconciles these findings by showing that it appears to be a matter of spatial context. Women in non-urban areas of Sweden increase their driving over time, while in urban areas men decrease their driving over time. Furthermore, paper IV corroborates an important contribution of (Kuhnimhof et al. 2012) to the European peak car literature: the largest reductions in young adults’ licencing and VKT per capita occurred already during the 1990s, which is too early to explain the levelling off of VKT per capita in the middle of the 2000 decade.

Previous literature has pointed out that car use trends appear to diverge between metropolitan areas and less densely populated areas (OECD/ITF 2013; Headicar 2013). However, this claim was limited in detail, for example based on comparing VKT per capita in cities versus national trends (Madre et al. 2012). Paper V is the first paper, to my

knowledge, to use large scale travel survey data of a metropolitan region over 30 years or more, to analyse changes in travel behaviour within a metropolitan region. The large sample size of the Stockholm County travel surveys enables spatial differentiation within the metropolitan area, while controlling for variables such as income, gender, trip purpose and mode. This is important because of the interaction of these variables and because the population increasingly sorts spatially by income.

Paper V links travel behaviour observations to the urban economy literature, which argues that agglomeration economies are stronger in larger and more skilled cities (E. L. Glaeser and Resseger 2010; E. Glaeser 2011; Behrens, Duranton, and Robert-Nicoud 2010). Traditionally, travel behaviour literature studies the micro-motives, constraints and opportunities of individual travellers or households. However, the population level outcomes in travel and long-term location and mode choices may not be apparent from studying individuals’ and households’ incentives alone. In Stockholm County, jobs, consumption activities and new housing are increasingly locating in the regional centre. I argue that this creates a reinforcing mechanism of increasing the attractiveness of the inner city, and that this is an important driver for the observed changes in travel behaviour.

Paper V puts together empirical evidence from several capital regions in Northern Europe. It identifies common patterns in travel behaviour: for example, bicycle use is increasing in inner cities and towns, while it is decreasing in rural areas. The results suggest that similar agglomeration types across Europe - in terms of city size, density and economy - rather than national territories are experiencing similar trends in travel behaviour. Paper V demonstrates that car use decreases and bicycling increases where economic, housing and activity densities are growing and road space is limited, for example in Stockholm and London. In London the extent of the transit supply expansion was much larger than in Stockholm. The Stockholm case study therefore suggests that other factors, apart from transit expansion, are important drivers. Paper V results indicate that an increasing concentration of activities in Stockholm’s urban core, large roadworks, parking limitations, and an increase in commercial traffic have increased road congestion. Congestion is one probable reason that residents of all income groups make fewer and shorter car trips within Stockholm County in 2015 than in 2004. Another reason is that people make fewer everyday trips in general (and more long distance trips). Nevertheless, lower metropolitan car use does not equal fewer cars or a general preference shift away from cars. Car access per capita in Stockholm County has remained stable on average from 2004 to 2015, which is a combined effect of diverging

trends between residential locations and age groups. And long-distance car trip frequencies have been increasing.

4 Discussion This thesis reconciles aggregate national trends in VKT with trends in private car travel among different socio-economic groups and in different spatial contexts. The findings in this thesis are of interest to planners of transport and land-use, and to policy makers at all levels of government.

The results suggest that there is no need to assume exogenous changes in attitudes to explain the aggregate changes in western nations’ VKT per capita in the early 21st century. However, this does not imply that changes in attitudes and life-styles are not relevant or important for behavioural changes. It seems likely that changes in attitudes and lifestyles are to a large extent induced by economic factors in the long run, and the two sets of factors are inseparable.

From a forecasting perspective, it is reassuring that most of the variation in VKT can be explained by economic, socio-demographic and land-use variables. However, the economic downturn and fast increase in fuel prices after 2008 was difficult to predict. The findings in this thesis are consistent with (Jong et al. 2007) in that uncertainty in input variables is a larger source of errors in transport forecasting than is uncertainty in model parameters. Long-term predictions of immigration, income- distribution, land-use, technology and settlement patterns may all add to the uncertainty over a longer time horizon.

This thesis highlights an important policy goal conflict for Stockholm and similar metropolitan regions: on the one hand, land-use and transport planning aims to reduce the need for travel and promote sustainable travel patterns, and on the other hand, regional plans aim for a more even distribution of resources and growth across different municipalities and counties. Concentrating growth in Stockholm’s walkable metropolitan centre contributes to objectives such as reduced carbon emissions, traffic safety, gender equality, economic growth, and crime prevention. However, planners also face needs to provide affordable housing, to integrate regional labour markets, and to supply smaller sub- centres and towns with public infrastructure, incomes and activities.

From a policy perspective, this thesis suggests that economic incentives are effective in steering private car use, even in high income countries and regions, and especially among people in urban areas that have good mode and destination alternatives. Fuel prices, or any cost that applies immediately and directly per trip or per VKT, appear to be more effective 15

at influencing driving decisions than fixed and long-term costs of car ownership. This is probably due to a combination of human bias towards present rewards (hyperbolic discounting), loss aversions when buying durables (Greene 2011), and rebound effects of price and fuel efficiency improvements (Stapleton, Sorrell, and Schwanen 2017).

The fact that urban men in Sweden, who were and still are relatively heavy car users, have reduced their driving over a 30-year period suggests that, given sufficient incentives, changes in personal car driving are a matter of opportunities to adjust.

Any policy aiming at reducing motor vehicle use would be wise to consider the incentive structure of access and use of company cars, delivery vans, and other commercial vehicles. For example, the congestion charges in Stockholm and London have been effective in keeping the highest valued trips on the road and thus increasing the share of commercial traffic. Now, to manage the growing commercial traffic and company cars, new instruments are needed, because commercial traffic is very inelastic to pricing (and more elastic to GDP).

This thesis relates societal trends, such as the rise of the knowledge economy and increasing gender equality, to changes in car use. I argue that urban agglomeration forces affect land-use, activity locations, population sorting, mode choice and trip decisions. I show that spatial context is becoming increasingly important in car use trends. Car use, travel behaviour, population and job growth increasingly diverge between city, suburban, and less densely populated areas in Sweden, England and similar countries. Consequently, national transport policy may in some aspects decrease in relevance, while cities, towns and rural regions have more to learn from similar type areas in other regions and countries. For example, in some metropolitan regions the pull effects of agglomeration on travel behaviour might be stronger than the effects of intentional land-use planning, which is the focus in much current policy analysis. Trends in transport, technology, equity and the economy are interconnected and need to be addressed as such.

Stockholm is world leading in the progress towards more gender equal societies and new uses of ICT. To the extent that these changes impact land-use, population and activity locations, and travel behaviour, the trends in Stockholm might be indicative of future trends in other cities. At the same time, there are signs of an increasing divergence in economic, population and travel behaviour outcomes between economically successful cities with highly skilled workers (e.g. London, Stockholm, Amsterdam and Copenhagen) and other cities, towns and rural regions that attract less population and economic activity.

Much of the existing research on car use and technological alternatives focuses either on countries or cities. Yet, traffic outside of metropolitan areas stands for the majority of VKT and transport greenhouse gas emissions in Sweden (though not in emerging economies). The alternatives to car use are more limited outside of metropolitan areas. This is why future land-use and the location of future population and activity growth are important for steering long-term trends in car use. The United Nations estimated in 2012 that 60% of the global area expected to be urban by 2030 had yet to be built (Secretariat of the Convention on Biological Diversity 2012), though most of this construction occurs in developing economies.

5 Limitations and future work This thesis uses aggregate VKT statistics and cross-sectional individual travel survey data, which come with the typical benefits and limitations of such data. For example, cross-sectional data does not enable distinctions between self-selection and causal effects of land-use on travel behaviour. Conversely, models based on aggregate time series data are limited in spatial and socio-demographic detail. Furthermore, only aggregate data about supply changes in public transport was considered. To capture the cost of driving, I have primarily considered real fuel prices, not quantifying changes in the cost of parking, car ownership and fuel efficiency gains. It is not obvious how and to what extent to consider the latter costs in a model of travel behaviour (Whitehead, Franklin, and Washington 2015; Odeck and Johansen 2016; Li, Sipe, and Dodson 2017).

We use simplistic models to investigate temporal changes in VKT per capita elasticities with respect to fuel prices and GDP per capita. If the objective had been to estimate the best elasticities possible, more advanced time series modelling would be advisable, to better account for long-term adaptations, imperfect price reversibility and absolute levels of fuel prices and GDP. This would also have required longer or more disaggregate time series data. Given the limited length and high aggregation level of our data, more advanced time series models would need to make several strong assumptions.

The analysis in this thesis is limited to the context of high income Western countries that have experienced reductions in VKT per capita in the 2000 decade. The findings cannot directly be transferred to rapidly growing Asian or Latin-American cities for example. Similarly, many of the findings for Stockholm County appear to apply to cities like London and Copenhagen, but not necessarily to European towns, regions and cities experiencing economic and population stagnation or decline.

The societal trends discussed in this thesis - such as increasing gender equality, increasing foreign immigration, urbanization, changing ICT use, and the shift to a knowledge/digital economy - are closely interconnected and occurring simultaneously. It is therefore not possible - and arguably not fruitful - to isolate the impact of each societal trend. A next step for further research would be to compare the observed travel behaviour trends in Stockholm County with those in cities, towns and regions with different economic, social, and land-use conditions.

While long-distance and international travel is increasing in Sweden, frequencies for everyday activities are decreasing in Sweden and England, in particular for shopping and leisure and among young people. This thesis suggests a probable relationship with changes in ICT use, but conclusive evidence is lacking. Measuring why trip frequencies are decreasing over time is difficult. If one were to interview people about the causes, they may not notice or remember why they reduced their trip frequencies over several years, and they would likely underestimate changes in their own behaviour and attitudes (Eliasson 2014).

The previous section discussed uncertainties in input variables to transport forecasts. A particular source of systemic uncertainty at the moment is the impact and timing of the changes that fleet-owned, self- driving, connected, and electric vehicles could have on the transport system. Currently, fuel costs are the primary direct cost of VKT (sometimes also parking and congestion charges), and vehicle ownership is nearly a fixed cost. This would change if and when car access has largely shifted to a per-ride service model. If, for example, car ownership should transition from today’s model of distributed ownership to a fleet of shared electric vehicles, the resulting changes in the cost and price structure of car use could have far-reaching consequences for travel behaviour, infrastructure needs, accessibility and economies. To steer such possible systemic changes requires 1) defining a desirable future of transportation, including the required trade-offs, and 2) research towards informing policies and technologies that can guide the trajectory of this industry.

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