This paper applies the regression discontinuity (RD) method to evaluate the effects of removing the London western charging zone (WCZ) on traffic flow and vehicle emissions. A total of 525 road sections are included for a period of 3 years (2008, 2010, and 2013). We first test the continuity of the confounders, and the results show that all confounders are continuous at the cutoff. Then the effects of implementing and removing the western charging zone scheme are estimated respectively. The results suggest that the AADT is reduced by about 31.1% within the western zone after implementing the WCZ scheme. On the contrary, without expansive congestion fees after calling off the WCZ, the number of vehicles within the western zone is increased by around 26.4%. Regarding the effects of the WCZ scheme on the emissions of vehicles, the results indicate that the vehicle emission of NOX and CO2 is decreased by around 29% and 33% respectively within western charging zone. In contrast, the emission of NOX and CO2 is increased by 24% and 21% respectively after removing the WCZ. After controlling for the time trend effect, the results indicate that there are residual effects of the WCZ on AADT and the vehicle emission of CO2 (AADT: 4412 vs 3011, Time trend: -1100; CO2:134μg/m3 vs 70μg/m3, Time trend: -30μg/m3). However, such residual effect on the vehicle emission of NOX is not significant.

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