Effects of delineation signs on driving behavior in expressway tunnel curves

Driving on curved roads presents higher traffic safety risks compared to straight sections. However, existing research has primarily focused on open road curves, with limited studies addressing safety measures for tunnel curves. This study aims to evaluate the effects of curve delineation signs-such as chevrons, horizontal arrow signs (HASs), and retro-reflective arches (RAs)-on driver behavior at tunnel curves.

The experimental design included two types of flat curve radii and four delineation sign schemes. A driving simulation experiment was conducted with 37 participants in a one-way, two-lane tunnel curve scenario, analyzing their driving behavior at tunnel curves and key curve points.

Chevrons and HASs effectively encourage drivers to slow down when approaching gentle curves but have a limited deceleration effect on sharp curves. Nonetheless, both signs contribute to reducing vehicle speed in both sharp and gentle curves. In contrast, the RA significantly enhances deceleration in both curve types, prompting drivers to decelerate earlier and enter the curve at a lower speed, thus lowering the average speed through the curve segment. While chevrons, HASs, and RAs all aid in adjusting lane positions and reducing lateral control risks, their effectiveness in lateral control remains limited.

HASs and RAs can serve as viable alternatives to chevrons in tunnel curves. In particular, the installation of three visible RAs is recommended for sharp tunnel curves to improve traffic safety.