Towards linking driving complexity to crash risk

Abstract

The purpose of this article is to present insights into the relationship between complex traffic flow phenomena on urban motorways and crash risk. Unstable or congested flow can trigger low speed/high density clusters (e.g. nucleations or shockwaves) creating ‘surprise elements’, therefore sharply increasing the cognitive workload for motorists. When combined with reduced road space and freedom to perform needed manoeuvres (e.g. lane changes), conditions can exceed the physical or mental capability and hence increase the likelihood of human error. There is overwhelming evidence that high traffic density drastically increases the crash risk. Some density concentrations can be avoided through appropriate planning and real-time traffic control, resulting in a reduction in crashes. Modern measurement devices allow for the analysis of individual vehicle behaviours such as ‘Brake’, ‘Speed alert’ or ‘Lane change’ events and show promise in providing robust data to further exploring what makes dense traffic complex. This allows establishing relationships between “events as elementary units of exposure” and crash occurrence resulting in a new way of understanding crash rates. These relationships are important to predict crashes, identify high-risk locations, and establish suitable measures for crash reduction.

New Understanding of Motorway Crash Risk From Newly Available Metrics

“…Drivers' reaction times vary and can be affected by the context that drivers face (Markkula et al, 2016). Braking efficiency also needs to be considered in the overall stopping distance (Zurlinden et al, 2022) which varies from vehicle to vehicle. Differential braking efficiency between consecutive vehicles can result in dangerous situations if the vehicle behind has less braking efficiency than the vehicle in front (e.g., truck following car).…”

Can I Stop? Considering Opportunities to Influence Multidisciplinary Factors That Result in Crashes

“…This is unrealistic due to variations in motorists' performance capability resulting from the dynamics of certain conditions which cannot be seen nor perceived. The latter, in complex surroundings such as multi-lane motorway carriageways with thousands of vehicles lane changes per km/h (Zurlinden et al, 2020), can suddenly and unexpectedly change the legal situation (e.g., when a lane changing vehicle halves the distance to the vehicle in front). This is not only challenging for humans but also for autonomous vehicles.…”