The Impact of Low Emission Zones in Cities

Low Emission Zones (LEZs) are now a core urban transport policy for reducing harmful emissions from road traffic and improving air quality in busy city centres. By restricting or charging the most polluting vehicles, they directly target a major source of nitrogen dioxide and particulate matter, supporting wider goals around public health, climate mitigation and liveable streets. LEZs are being introduced or strengthened in many European and UK cities, often alongside congestion charging, active travel investment and public transport improvements, making them central to sustainable mobility strategies.

Despite their rapid rollout, key questions remain about how, and for whom, LEZs deliver benefits. Studies report improvements in particulate pollution and some health outcomes, but findings are mixed for other pollutants and there are important uncertainties about distributional effects, behavioural responses and longer-term dynamics. This creates a strong need for rigorous, comparative research that can inform future policy design and help cities integrate LEZs into broader decarbonisation and equity agendas.

This PhD project will evaluate the direct and indirect impacts of Low Emission Zones using advanced econometric and spatial-temporal methods. The student will identify a set of plausible impact channels, such as air quality, health and well-being, traffic patterns, equity and economic activity, and assemble relevant datasets at appropriate spatial and temporal scales. The core of the project will be the design and implementation of causal models exploiting staggered introductions, boundary changes or tightening of standards across multiple cities, using approaches such as difference-in-differences, event-study designs and related quasi-experimental techniques.

A central objective is to understand heterogeneity: why similar policies appear to have different effects across locations and population groups. The student will explore factors such as baseline pollution, vehicle fleets, enforcement intensity, complementary policies and socio-demographic characteristics, testing how these shape outcomes and distributional impacts. There will be scope to examine spillover effects, for example the displacement of traffic and pollution to neighbouring areas, and to consider dynamic responses such as fleet renewal and changes in travel behaviour.

Alongside the quantitative impact evaluation, the student will undertake a systematic literature review of LEZs and closely related road-use policies. This review will synthesise existing evidence on environmental, health, equity and economic outcomes, identify methodological strengths and weaknesses, and highlight the most important open questions for future research and policy. It will also help to position the thesis at the frontier of an emerging interdisciplinary field spanning transport, environmental and health economics, urban planning and public policy.

The project is designed to produce a coherent body