Smart and conventional road delineation: impacts on driver behavior under nighttime dry and heavy rain conditions.

Driving on horizontal curves on rural highways is a well-known road safety concern, especially when limited visibility makes it harder for drivers to anticipate the road ahead and adjust speed and trajectory. Conventional solutions - unlit markings and passive road studs (PRS) - rely on vehicle headlamps' illumination and provide limited improvements in visual range. Technological advancements, however, are reshaping how road safety challenges are tackled. In this context, two self-luminous technologies designed to improve road visibility and support drivers' anticipation of road geometry were investigated: active road studs (ARS) and photoluminescent road markings (PRM). Two within-subject experiments investigated how curve delineation treatments (unlit, PRS, ARS, and PRM), radius (120 m vs. 440 m), direction (left vs. right), and distance affect speed and lateral position, both in dry (Experiment 1) and in heavy rain (Experiment 2) nighttime conditions. Each experiment included four two-lane rural highway scenarios (∼15 min each) with 24 horizontal curves. Fifty participants (21-55 years old, 23 women) underwent both experiments. PRM improved drivers' performance: participants drove at lower speeds and kept the vehicle farther from the edge line under both dry and heavy rain conditions. Conversely, unlit markings and ARS resulted in higher speeds in dry and heavy rain, respectively. PRS reduced speed in dry conditions compared with unlit markings, while no effect was observed under heavy rain. Overall, results suggest that PRM may provide meaningful safety benefits on curves, particularly where visibility is compromised. Future studies should explore whether familiarity with technologies modulates behavior and long-term effectiveness.