01624349

Component

This paper aims to estimate the causal effects of the London congestion charge (LCC) on road casualties. Difficulties in providing valid counterfactual outcomes for treatment units in absence of an intervention can undermine inference derived from causal models. In this paper, a synthetic control group is constructed to approximate the casualty number that the central London area would have experienced in the absence of the LCC. The treatment effect can be estimated by comparing the casualty number between London and the synthetic control group in the post-treatment period. This method overcomes drawbacks in conventional comparative-study methods and the validity of the approach can be tested by a placebo study. The synthetic control group has similar characteristics as London and mirrors the trend of casualty number in London. The results show that the total casualties within the charging zone is reduced by 4.29%, while the reductions in slightly and seriously injured are 5.05% and 12.12% respectively. The results of placebo-controlled study show that the estimates of the effects of the LCC are all significant at the level of 95%. The results suggest that the synthetic control methods can be applied as an alternative when there is no suitable control group in the conventional methods. The significant reduction in casualty number is most likely due to the fact that the traffic volume has decreased since the introduction of the LCC, coupled with the fact that the total number of accidents decreases as the traffic volume decreases.

This paper was sponsored by TRB committee ANB20 Standing Committee on Safety Data, Analysis and Evaluation.

01618707

17-01497

English

11p

2017

Transportation Research Board 96th Annual Meeting

Digital/other

Figures; Maps; References (25) ; Tables

Fatalities; Highway safety; Traffic congestion; Traffic volume; Urban areas

Greater London; London (England)

Highways; Operations and Traffic Management; Safety and Human Factors

Transportation Research Board Annual Meeting 2017 Paper #17-01497

TRIS, TRB, ATRI

Dec 8 2016 10:29AM