Published article: Congestion by accident? A two-way relationship for highways in England. (Journal of Transport Geography, 2017) Abstract: This paper aims to estimate the causal effect of accidents on traffic congestion and vice versa. In order to identify both effects of this two-way relationship, I use dynamic panel data techniques and open access ‘big data’ of highway traffic and accidents in England for the period 2012–2014. The research design is based on the daily-and-hourly specific mean reversion pattern of highway traffic, which can be used to define a recurrent congestion benchmark. Using this benchmark, I am able to identify the causal effect of accidents on non-recurrent traffic congestion. A positive relationship between traffic congestion and road accidents would yield multiplicative benefits for policies that aim at reducing either of these issues. Additionally, I explore the duration of the effect of an accident on congestion, the ‘rubbernecking’ effect, as well as heterogeneous effects in the most congested highway segments. Then, I test the use of methods which employ the bulk of information in big data and other methods using a very reduced sample. In my application, both approaches produce similar results. Finally, I find a non-linear negative effect of traffic congestion on the probability of an accident. Research in progress Shopping externalities and retail concentration: Evidence from Dutch shopping streets. (with Hans Koster and Jos van Ommeren; in submission) Abstract: Why do shops agglomerate in shopping districts? According to theory, shops benefit from shopping externalities, because customers walk shorter distances between shops. We identify shopping externalities by estimating the effect of footfall – the daily number of pedestrians that pass by – on shop rents and vacancy rates, which together determine the rental income of a shop. We address endogeneity issues by focusing on spatial differences of footfall between intersecting shopping streets. Our estimates imply an elasticity of footfall with respect to rental income of about 0.25. A shops’ average monetary benefit of one additional pedestrian passing by is estimated to be about €0.004 per year. It is also shown that footfall reduces shop vacancy rates considerably. We estimate that the average subsidy for retail firms in high-footfall areas should be about €3,338 per year (6.5 percent of the yearly rent). Express delivery to the suburbs. Transportation effects in Europe’s heterogeneous cities. (with Miquel-Angel Garcia Lopez and Elisabet Viladecans Marsal; in submission) Abstract: This paper provides evidence for the causal effect of the highway and railway infrastructure on the suburbanization of population in European cities using a unique dataset of 579 European cities during the period 1961-2011. We find evidence that an additional highway ray displaced approximately 9 percent of the central city population in European cities, while we find no significant effect for the railways on average. When employing the full time span covered by our data, we find that highways caused more suburbanization in the period 1961-1981, when urban growth in Europe was on its peak. Our heterogeneous analysis suggests that Roman and Medieval cities were more resilient to this process. The existence of historical amenities in European cities appears to provide a reasonable explanation for these differences. Highway congestion and air pollution in Europe’s cities. (with Miquel-Angel Garcia Lopez and Elisabet Viladecans Marsal) In this paper, we test and confirm the ’fundamental law of highway congestion’ (Downs, 1962, 1992) for the cities of Europe. Our identification strategy is based on four different historical transportation networks in Europe that we use as instruments and on panel data techniques. We also find that traffic increases the emissions of some of the most harmful urban air pollutants. Our heterogeneous analysis shows that the effect of highway construction on traffic congestion and urban air pollution is higher in cities without tolls, which substantiates congestion pricing, and in cities without subways, which corroborates rapid transit policies. We derived a back-of-the-envelope calculation, suggesting that the cost of air pollution caused by the new highways in the period 1985-2005 in Europe’s cities was 6.3 million euros in the period 1980-2000, which is arguably small.