Experimental study on the efficacy of retroreflective rings in the curved freeways tunnels

This study analyzes the impact of different numbers of visible retmreflective rings on the drivers' ability to perceive the curvature in curved freeway tunnels under different small radii. A driving simulator was used to conduct simulation tests on the two visual guiding schemes in curved tunnels with chevron alignment signs and retroreflective rings. The drivers' curve illusion and reaction time were tested to assess their ability to perceive curvature; the tests data were analyzed using OriginLab. In the unimproved scenes, the drivers overestimated the radii, at least, 35%, and the values of reaction time were at most 5.251 s. In the scenes where four visible chevron alignment signs were used, the curve illusion and reaction time under different radii were marginally decreased; only at the radii of 200 m (6.03%) and 400 m (6.12%), the drivers could reach a better perception of curvature. In the scenes with three visible retroreflective rings, the degree of curve illusion under different radii was at most 5%, and the values of reaction time were, at least, 37% lower than the unimproved conditions. The scheme of three visible retroreflective rings was more conducive to improving the drivers' perception of curvature and controlling the reaction time within a reasonable range. The fitting analysis of the logistic function revealed that the fitted curves' inflection points between curve illusion and the number of retmreflective rings under different radii were close to 3, where the degree of the curve illusion reached the lowest. Meanwhile, the drivers' reaction time under different radii negatively correlated with the number of visible retroreflective rings. When the number of retroreflective rings was more than four, the reaction time exhibited a convergence trend, suggesting that the increasing number of visible retroreflective rings exerted a limited effect on shortening the reaction time. Hence, this study recommends utilizing three visible retroreflective rings to guide the drivers' sight in the curved freeways tunnels.