Driver behavior in road tunnels association with driver stress and performance

Complex traffic environments can affect driver stress and driving performance negatively. Driving through tunnels can be particularly stressful, and these segments have been associated with higher crash rates. However, the constraints of the natural environment (e.g., mountains, waterways) often restrict the flexibility to make major modifications in tunnels. The purpose of this study was to evaluate stress as drivers traversed along an interstate route that included tunnel and nontunnel segments, as well as a 75-m transition period before the tunnels. Data from 50 drivers, including information from electrocardiogram recordings such as heart rate and standard deviation of interbeat intervals (SDNN), were collected. Driving performance measures included vehicle speed and braking. Multivariate and univariate analyses of variance were used to identify increases in drivers' stress during several road segments: the transition to a tunnel entrance, within a tunnel, and open road segments. The largest variations in performance measures were observed in tunnels, followed by the periods in transition segments. Evaluation of continuous speed profiles along the route showed that drivers tended to decrease their speed before entering a tunnel and increase speed just before exiting a tunnel. The highest level of stress (denoted by the largest positive change in heart rate and lowest variability in SDNN) was observed along the transition segments, followed by the tunnel segments. Identifying situations in which drivers may experience higher levels of stress and the corresponding impact on driving performance is important for future road and tunnel designs.