Harnessing the speed stability evaluation index to achieve sustainable urban traffic safety

Speed stability can be defined as the degree to which a vehicle can travel with a smooth and predictable acceleration and deceleration. It is evident that increasing speed stability enhances a vehicle’s capacity to maintain a consistent velocity, thereby facilitating more stable traffic flow, which can enhance traffic safety. In Korea, the prevailing approach to speed management entails the enforcement of speed limits with the objective of promoting vehicle deceleration. However, this strategy does not consider the vehicle’s speed stability in relation to geometric and traffic conditions specific to each road segment. This study proposes a methodology for determining speed stability by developing a speed stability evaluation index. The speed stability evaluation index is derived from several key speed and safety-related variables through correlation test and random forest feature importance analysis. The study also proposes a methodology for evaluating the level of speed stability for each road segment and time period, based on vehicle trajectory, traffic crash, and road geometry data. The thresholds for these levels were calculated with reference to regional characteristics and validated through correlation analysis with crash occurrence patterns. Finally, policy implications for preparing countermeasures for each level were presented. The approach presented in this study is expected to contribute to the creation of a safe and stable urban road traffic environment by encouraging voluntary competition to ensure traffic safety and stability among local governments.