City-level policies are increasingly recognized as key components of strategies to reduce transport greenhouse gas emissions. However, at a global scale, their total efficiencies, costs and practical feasibility remain unclear. I will present a few papers in which we show that, thanks to the recent increase in local data availability, urban economic and transport models can help analyze and simulate the potential, the welfare impacts and the inequalities created by transport policies in cities in different countries. Our results highlight that there is no one-size-fits-all policy, but that, with city-specific strategies, it seems generally possible to sharply reduce emissions, over 15 to 20 years, while increasing the average welfare of the inhabitants. However, inequality creation by the policies appears as one of the main challenge, as it raises ethical issues and threatens the political acceptability of the policies. How to overcome this challenge still appears as a research gap.