Association of crash potential of powered two-wheelers with the state of traffic stream

Abstract

Powered two-wheelers (PTWs) are widely used in low- and middle-income countries for short-distance trips. PTWs have been preferred over the other modes because they are relatively faster in densely populated cities, given their smaller size and higher flexibility. Nevertheless, PTWs pose a higher crash risk, especially in mixed, weak lane-disciplined traffic conditions. There is insufficient evidence emphasizing the safety aspects of PTWs and their relationship with the traffic states. The present study aims to fill this gap by performing a proactive safety assessment using a surrogate safety indicator called Anticipated Collision Time (ACT), which captures the conflict types and the overall crash risk. Unlike most Surrogate Safety Measures (SSMs), the ACT considers the evasive actions of the vehicles, which is more critical for the safety assessment of PTWs. Further, this study investigates the PTW crash frequency, severity, exposure, and evasive actions and their relationship with the traffic states, using various indicators derived from ACT. The results imply that the frequency, exposure, and severity of PTW crashes strongly correlate with Area-Density, a measure of traffic crowdedness, and the proportion of PTWs involved in an unsafe situation increased with Area-Density. The most prominent crash type observed for the PTW was the sideswipe, which can be attributed to the unique riding characteristics of PTWs, such as filtering, weaving, and tailgating. It was observed that the coefficient of variation of PTW speed was a significant factor affecting the conflict severity. The PTW riders were found responding early to an unsafe situation in congested and free-flow conditions, which indicates they are more cautious during these traffic states. However, during the capacity conditions, the riders were less vigilant. This study’s findings will be useful for targeted road safety interventions and campaigns to improve PTW safety. Additionally, the knowledge acquired from this study can be used to develop customized advanced riders’ information systems considering the correlation between crash likelihood and traffic state. Also, understanding the most frequent and severe crash types that PTWs involve in can aid in developing customized rider wearables.