- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
This paper analyses how the effects of fixed speed cameras on road casualties vary across sites with different characteristics and evaluates the criteria for selecting camera sites. A total of 771 camera sites and 4787 potential control sites are observed for a period of 9 years across England. Site characteristics such as road class, crash history and site length are combined into a single index, referred to as a propensity score.We first estimate the average effect at each camera site using propensity score matching. The effects are then estimated as a function of propensity scores using local polynomial regression. The results show that the reduction in personal injury collisions ranges from 10% to 40% whilst the average effect is 25.9%, indicating that the effects of speed cameras are not uniform across camera sites and are dependent on site characteristics, as measured by propensity scores. We further evaluate the criteria for selecting camera sites in the UK by comparing the effects at camera sites meeting and not meeting the criteria. The results show that camera sites which meet the criteria perform better in reducing casualties, implying the current site selection criteria are rational.
6. Discussions and conclusions
As an important part of the UK Government’s ten year road safety strategy, the national safety camera programme is expected to regulate driving speeds and reduce casualties. It would be very rash to conclude that safety cameras are uniformly effective in reducing road casualties. However, a series of issues related to speed cameras have never been touched before, such as how effectiveness varies by site characteristics and under what conditions speed cameras perform most effectively. To date there has been no independent study using advanced state-of-the-art causal methodologies to answer these questions. This study contributes to the literature by applying causal models to estimate heterogeneous treatment effects of speed cameras on road safety.