Conspicuity of Various Colored Express Lane Delineators: Matching or Contrast?

Abstract

Express lanes (ELs) are an increasingly accepted traffic management tool for congestion relief and traffic efficiency. White, yellow, and orange vertical delineators are typically used for lane separation and channelization applications. However, upcoming changes to sections of the Manual on Uniform Traffic Control Devices that would affect the current use of the orange retroreflective delineators will have a statewide impact on current and future ELs. The availability of a wide array of delineator colors and the potential range of application purposes brings into question this blanket requirement. The ineffective use of color in roadway design could lead to an increase in driving errors/response time, driver fatigue, loss of situational awareness, and increased workload. Driver perception and reaction time is shown to be affected by visual factors, such as color, luminance, distractions, and speed. The objective of this study is to determine the impact of color usage and other environmental and demographic factors on driver perception. A fractional factorial experiment was designed to study the EL delineator color selection using a driving simulator and an eye-tracking device. The potential factors included time of day (night versus day), visibility (high versus low), traffic density (high versus low), and road surface type (concrete versus asphalt). Some 176 subjects were selected to participate in the experiment. It was found that, in general, white was the quickest to be noticed, while black took the longest time to perceive. Furthermore, it was found that delineators were generally more noticeable under night-time conditions, likely because of the standard use of retroreflective striping on delineators.