Traffic accidents and delays present contrasting pictures of traffic resilience to coastal flooding in the San Francisco Bay Area

Abstract

Global climate change is intensifying coastal flood events and increasing the risks of traffic disruption in low-lying, coastal communities. Efforts to understand the differential impacts of traffic disruption on communities have led to the concept of traffic resilience, which captures the degree to which a traffic system can recover from the disruption of traffic flows or changes in road conditions. Existing proxies of traffic resilience are focused on the relationship between the structural characteristics of the road network and travel time delays but lack the important dimension of road safety. In this study, we quantify traffic resilience in terms of the change in the rates of non-highway car and pedestrian accidents during the 5--10 am time period as a result of coastal flooding in the San Francisco Bay Area for the 2020--2040 period. We combine a regional traffic model with statistical regression models that relate traffic volumes to historical accident rates. We simulate traffic patterns under a range of coastal flood water levels and project non-highway car and pedestrian accidents rates for communities. Our results show that the flooding of highways forces commuters onto local roads passing through urban and suburban communities, causing a spike in accident rates during peak-hour traffic. As the water level rises, peak-hour accident rates are projected to increase in communities across the region. Unlike travel time delays which increase sharply at higher water levels, region-wide peak-hour accident rates increase the most at lower water levels. Thus, for low-to-moderate intensity flood events, accidents are potentially a greater concern than delays for communities.

Enhancing the resilience of road networks to flooding

“…In response to concerns about the frequency and severity of natural hazards and extreme events, the concepts of road resilience, logistics and planning have received increasing attention in the field of emergency management in recent years. The international academic and policy circles have also recognized the need to strengthen the resilience of our road networks [2,[14][15][16].…”