Reflective Properties and Lighting Quality of Urban Asphalt Roads in a Full-Service Cycle: A Longitudinal Study in Zhejiang Province, China

Abstract

To optimize the lighting design of urban roads in China and improve traffic safety, the present study conducted a 10-year longitudinal experiment on urban asphalt roads in Zhejiang Province, China, and analyzed variations of the road surface’s reflective properties and lighting quality with different service lengths, surface areas, and observation angles. The results showed that these roads were R2 roads with low resilience and strong directional reflection. The average luminance coefficient Q0 reached maximum and minimum at the beginning and after around one year of service, respectively. After four years of service, Q0 was about 80% of its initial value and remained stable. The specularity factor S1 reached a maximum of around two years of service. The average luminance Lav was approximately 35%, and overall luminance uniformity U0 was 31%, lower than that of R3 roads during the toughest period of the service life. If the lighting design follows the 1° observation angle r-table recommended by the specification, high Lav and low U0 occur for roads like expressways, leading to a significant increase in traffic safety risks; collector roads may suffer from insufficient Lav. Urban asphalt roads in Zhejiang Province, China, should use the R2 road standard and increase the design value of Lav by 35–45%, and high-level roads should increase the design value of U0 by 40%. The present study will provide scientific references for the design of lighting for urban roads in China, thus promoting long-term sustainable traffic safety in cities.