Roadway Illumination Level Assessment for Driver Safety and Comfort: A Multimodal Human Factors Evaluation of Visual Behavior, Physiological Arousal, and Driving Performance in a High-Fidelity Driving Simulator

Abstract

Nighttime driving remains a major road safety concern because reduced illumination can impair visibility, delay hazard detection, and increase visual strain. Although roadway lighting is intended to improve safety, greater brightness does not always produce better driving conditions. Excessive illumination may introduce glare, discomfort, and unnecessary energy use without meaningfully improving driver response. This thesis investigates how different nighttime illuminance levels influence driver safety and comfort by examining their relationship with multimodal safety-related measures, with the aim of identifying the illumination level that best supports visual detection, driving performance, physiological stability, and perceived visibility, comfort, and safety. A controlled mixed-design experiment was led in a high-fidelity virtual driving simulator using a replicated real-world street environment under three nighttime illuminance levels, low, medium, and high, established in accordance with roadway lighting standards. Thirty licensed drivers participated in the study, equally divided between younger adults aged 20 to 45 years and older adults aged 65 years and above. Driver response was evaluated using a multimodal framework integrating eye-tracking (Time to First Fixation (TTFF), Dwell Time), simulator-based driving measures (PRT, Speed, Hazard-related Deceleration), physiological markers (Heart Rate (HR), Electrodermal Activity (EDA)), subjective ratings of perceived visibility, comfort, and safety, and qualitative feedback. The results showed a clear relationship between illuminance level and driver response. Low illuminance was associated with delayed visual detection, slower hazard response, higher physiological arousal, and poorer ratings of visibility, comfort, and safety. Increasing illuminance from low to medium improved TTFF and PRT, enhanced perceived visibility and comfort, and supported greater physiological stability, whereas increasing illuminance from medium to high produced little additional benefit and occasionally introduced glare-related discomfort. Older adults showed higher physiological arousal and more conservative braking behavior than younger adults, but both age groups followed the same overall pattern across illuminance levels. Overall, the findings show that effective nighttime roadway lighting is not achieved by maximizing brightness, but by selecting an illumination level that supports visual effectiveness, driver response, comfort, and physiological stability. Among the conditions examined, medium illuminance provided the most favorable overall balance for safer and more efficient driving. These findings provide practical guidance for roadway lighting design and planning by suggesting that moderate illumination may offer the most effective balance between safety, comfort, and physiological stability.