Research over the past two decades has revealed useful insights about the night visibility needs of the driver, stimulated efforts to improve the night visibility of traffic signs, and established measures of effectiveness for evaluating and monitoring night visibility of traffic signs. The knowledge gained has been translated into new materials for enhancing visibility and improved agency practices for managing traffic signs. Despite the importance of night visibility established in the research efforts, it is not uncommon to find traffic signs on the highway system that are barely visible at night. It is well known that crashes are more likely to occur at night despite lower traffic volumes and that this trend has persisted for more than 20 years. The FHWA has been at the forefront of efforts to improve the night visibility of traffic signs and to ensure that in-place signs are maintained to levels that meet driver needs. This paper describes efforts to develop minimum levels for sign retroreflectivity as a surrogate of night visibility. Such minimum levels have not previously been established despite the recognition of the need to illuminate or reflectorize signs as far back as the 1935 Manual of Uniform Traffic Control Devices (MUTCD). This paper provides background on the night-time visibility problem, describes the proposed minimum levels for traffic sign retroreflectivity, and discusses various issues cited as impediments to implementation (A). For the covering abstract of the conference see E217780.
Samenvatting