An analysis of vulnerable road user crashes in Alaska using spatio-temporal methods

Abstract

This study presents a two-part investigation into the spatial patterns of crashes and safety of vulnerable road users (VRUs). VRUs, cyclists and pedestrians in this context, represent approximately 18% of traffic fatalities in Alaska annually. However, existing studies on VRU safety in Alaska are limited and causal factors and effects of safety projects are not well understood making it difficult to implement targeted and strategic approaches to improve VRU safety. To that end, the objectives of this research are two-fold: 1) analyze spatial interactions of VRU crashes involving risk tolerant behaviors; and 2) evaluate the effectiveness of Highway Safety Improvement Program (HSIP) projects in achieving VRU safety outcomes. First, risk-tolerant behaviors among VRUs, namely alcohol consumption, suspected drug use, and lack of safety gear, are considered using Anchorage as a case study. Network-based spatial methods such as kernel density estimation, nearest neighborhood and K-function analysis, along with other network functions were employed to identify crash clustering and spatial dependencies. Results suggest statistically significant clustering is exhibited by crashes involving alcohol or drug use for both cyclists and pedestrians. Results also revealed spatial dependence between cyclist crashes and pedestrian crashes for the same risk-tolerant behaviors. Moreover, crashes involving cyclists who were not wearing helmets or safety gear exhibited significant spatial clustering. Second, explicit and implicit safety benefits of HSIP projects were evaluated using a before-after approach to determine the extent to which safety projects were successful in reducing crashes. Frequency and injury severity for VRUs. The analysis found mixed results. Some projects and project types demonstrated clear safety benefits while others showed neutral or negative outcomes. Additionally, VRU-specific project types were found to have more explicit safety benefits for cyclists than they did for pedestrians and that non-VRU specific project types seemed to exhibit more implicit safety benefits for pedestrians when compared to cyclists. These findings offer valuable insights for improving VRU safety in Alaska and serve to better inform the HSIP process including more robust methods for network safety screening, introduces new variables for consideration in the project selection process, and presents a more comprehensive approach for post-project evaluation.