The modelled impact of low traffic neighbourhoods (LTNs) on air pollution: findings from 5 schemes in London.

Low traffic neighbourhoods (LTNs) are area-wide schemes that remove through motor traffic from residential streets. These schemes are controversial, and one focus for this controversy has been the potential for traffic diversion to increase air pollution on surrounding 'boundary roads'. In this study we estimate the air pollution changes and associated health impacts attributed to the implementation of five LTNs in London, UK. We did so by implementing a full-chain model covering changes in traffic-related emissions, air pollution, small-area level exposures, and health impacts across select outcomes. Model inputs included observed before-and-after changes in traffic volumes, traffic speeds and congestion. Inside LTNs, we found an average change of -0.157 μg/m3 for NO2 (equivalent to -0.87% in relative terms), and -0.0276 μg/m3 for PM2.5 (-0.33% in relative terms). In areas containing boundary roads, we found a mixture of positive and negative changes, with net effects slightly below zero (-0.18% for NO2, -0.06% for PM2.5). Thus, contrary to concerns, air quality did not deteriorate in boundary road areas on average. There was no evidence that the average improvement in air quality varied by area-level ethnic diversity or deprivation, but there was evidence that areas with the highest baseline pollution saw the smallest benefits. Overall, across LTNs and their surrounding areas, we estimated that the air quality improvements due to the LTNs translated into a -0.01% relative change in the number of deaths per year (-0.05% inside LTNs), and a -0.02% to -0.04% change in new cases of childhood asthma (-0.08% to -0.19% inside LTNs). We conclude that LTNs typically improve air quality in London but, at the current modest scale of implementation, their effect is small.