Analysis of Nighttime Visibility of In-Service Pavement Markings

Traditionally, retroreflectivity is used to quantify the visibility of traffic control devices, including pavement markings. However, retroreflectivity is a physical property of a material that is used as a surrogate for luminance. By itself, retroreflectivity is limited to describing the visibility of pavement markings at night. One way to quantify the visibility of pavement markings at night is to assess the visibility level (VL) from the perspective of a driver's visual demands. This paper introduces an extended VL model for pavement markings that is based on previous research on VL modeling. This model was used to determine the visibility of in-service pavement markings along lit and unlit sections of highway in Anchorage, Alaska. The measured retroreflectivity of the pavement markings was compared with the FHWA proposed minimum retroreflectivity levels for pavement markings, and the calculated VL was compared with the implied visibility of the pavement markings (also calculated from the VL model) as derived from the FHWA proposed minimum retroreflectivity levels. The results indicated that the visibility of areas with continuous roadway lighting appeared to be more than adequate, despite low retro-reflectivity levels. The benefit of the roadway lighting was most evident when the retroreflectivity of the pavement markings was relatively low and at the longer distances tested (54 and 64 m).