Speaker: Stephan Thies
Title: The Welfare Effects of Traffic Calming: Evidence from London’s 20 mph Limits
Abstract: Traffic calming, such as 20 mph speed limits, road closures, and low traffic neighborhoods, has become a popular tool in many cities to reduce road accidents and to curb the local externalities of motor vehicle traffic. Yet traffic calming is often contested as it can increase travel times for drivers. Unlike Pigouvian pricing, which has received substantial attention in the economics literature but is rarely implemented to regulate traffic, traffic calming has a priori ambiguous welfare consequences. This paper studies these trade-offs empirically in the context of Greater London. Combining GPS data with roadside monitors, I assemble a novel dataset tracking annual vehicle volumes and speeds on every road in London between 2010 and 2025. I document that during this period average speeds fell by about 10% despite declining traffic volumes. Exploiting the staggered rollout of 20 mph limits, I estimate how much the lower limits contribute to the decline, their effect on road collisions, and how they redistribute traffic across the network. I combine these estimates with hedonic estimates of residents’ willingness to pay for quieter, slower streets to quantify the net welfare effect of the policy and its distribution across neighborhoods.
