고속도로 과속단속장비 설치에 따른 통행속도 및 교통사고 변화 분석: 이중차분법과 전후비교방법의 비교

This study investigates the changes in highway speed and traffic accidents caused by the speed enforcement system(SES). For this, we constructed a data set collected from TAAS(Traffic Accident Analysis System), TMS(Traffic Monitoring System), and KEC(Korea Expressway Corporation) about traffic information of six sections in four highways, where the SESs were implemented. For the analysis, this study adopts the difference-in-differences method(DID) and before-after evaluation methods including the comparison group method(C-G)). The results show some interesting findings. First, highway speed decreased by about 5km/h after the SESs were implemented and the number of accidents also declined on average. Second, both the DID and the C-G shows similar average decrement in traffic accidents and speed, however the statistical significance of the effects are quite different. The DID results show statistically significant change in speed and insignificant change in accidents, while the C-G results shows reverse significance. Considering relative advantages of the DID method, the impact of the SES on the number of accidents can be overestimated in the C-G results. This implies that researchers and policy-makers need more attention to possibility of over- or under-estimation when an incomplete empirical analysis is conducted.