An evaluation of pavement markings and raised pavement markers at left exit lane drops

Abstract

Most highway engineers agree that freeway exit lane drops create problems in terms of safety and efficiency. A driver can create a hazardous situation when making a sudden lane change out of or into an exit-only lane. Since left exits already violate driver expectancy, the potential for a hazardous situation is greatly increased if the exit lane drop occurs on the left side of the freeway. As might be expected, a left exit lane drop is a far more serious problem than either of its individual components; more drivers are affected, interactions in the traffic stream are more turbulent, and the potential for confusion and accidents is substantially greater. Exit-only signs and pavement markings are two methods used to communicate an exit lane drop to motorists. Signs are a required treatment in the Manual on Uniform Traffic Control Devices while pavement markings are an optional treatment. Sign treatments include diagrammatic signs, modified diagrammatic signs, the use of the black-on-yellow EXIT ONLY panel on conventional signs, and other signs. Markings include alternative gore area treatments and wider, closely-spaced lane lines. The objective of this paper was to determine if these lane drop markings in conjunction with raised pavement markers improve motorist operations at left exit lane drops. To determine the effectiveness of the markings, driver behavior was examined during daylight and evening hours before and after the lane drop markings were installed. Driver behavior was measured using frequency of lane changes and erratic maneuvers, the positions of these behaviors, and the time of day. The before-and-after data indicated that the lane drop markings were an effective treatment at the left exit lane drop. Traffic maneuvers and lane changes were both significantly reduced between the before and after periods. The data also indicated that motorists Performed their lane changes, into and out of the exit-only lane, further upstream of the gore in the after period than in the before period. It is believed that the uniqueness of the lane drop markings further emphasized a changing situation to motorists (i.e. an exit lane drop), and encouraged those drivers who desired to either enter or leave the exit-only lane to merge quicker. Awareness of the impending lane drop also encouraged fewer erratic maneuvers. Consistent use of standardized markings treatments can provide several benefits such as improved driver expectancy at exit lane drops.