Modelling car traffic in cities

Mitigating car traffic represents one of the biggest challenges that urban areas must face. Congestion induces time and productivity losses as well as greenhouse gas emissions that reach levels soon unsustainable. Despite the urgency of the problem we have a poor theoretical understanding of the parameters controlling urban car use and congestion. Here, we review the main theoretical approaches to this problem. We then discuss a recent theoretical framework that allows to predict the share of car drivers, the CO2 emitted by cars and the average commuting time. We confirm these analytical predictions on 25 major urban areas in the world. In contrast with the commonly accepted paradigm, our results show that urban density is not the relevant variable controlling car-related quantities but rather are the city's area size and the density of public transport.