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Evaluation of Concrete Median Barrier Delineation Under Poor Visibility Conditions
Kari French, E.I.T., PENNDOT District 12-0

In partnership with West Virginia University, the Pennsylvania Department of Transportation conducted a study to determine the effectiveness of concrete median barrier delineation under poor visibility conditions. Concrete median barrier delineators are reflective or light emitting devices that are placed in series on a median barrier divider between opposing directions of traffic. The specific type of median barrier addressed in this study is the safety-shaped, F-shaped or “jersey” barrier. Due to durability problems caused by vandalism and the affects of adverse environmental conditions in the roadside area where they are mounted, this delineation causes a significant maintenance problem for the Department. Also during poor visibility conditions, particularly fog and snow, there is a perceived increase in the frequency of sideswipe collisions with the barrier.

A nationwide survey of concrete median barrier delineation was conducted, and it was found that several differences between the current PENNDOT standard and their peers exist. Furthermore, there was little guidance provided by the nationwide survey or in a review of scholarly literature with respect to delineation of these barriers during poor visibility conditions. As such, there was an opportunity to evaluate the PENNDOT standard for concrete median barrier delineation, particularly as it relates to poor visibility conditions. Several field experiments were conducted, and are described below.

First, it was desired to test the effect of delineator configuration and spacing on driving performance under poor visibility conditions. Consequently, four 1800-ft long test sections were established on US 40 in Fayette County, Pennsylvania, just west of the crest of Summit Mountain. Two sections are in the upgrade direction and two are in the opposing lanes in the downgrade direction. Different delineator configurations /spacings were placed in each test section, and speed data collected at each test section under poor visibility conditions.

The vehicular speeds through each section are an indicator of visibility. Higher speeds are indicative of “anticipatory” driving, which results when the driver has better visibility. Under poor visibility conditions, when vehicular speeds are very low overall, the delineator configuration that yields the highest speed will be judged to have been the most effective in conveying the alignment of the roadway to the driver. Based on the visibility tests, it was found that a single side-mounted delineator near the bottom of the barrier in conjunction with a top-mounted delineator, provided the best guidance for the driver during poor visibility conditions. It was also determined that when the longitudinal spacing between the delineators is reduced, they provide better guidance during times of poor visibility.

Second, the harsh environmental conditions present in the roadside environment where delineators are mounted results in delineators falling off of the barrier with such frequency that it causes maintenance problems for the Department. This is particularly true during the winter months. Therefore, a test section was setup on SR 119 just north of Connellsville, Pennsylvania to test three different types of adhesives, Liquid Nails, Title Bond, and Peel-n-Stick. Each adhesive type was used to attach 34 delineators to the barrier in September of 2001. The survival rate of each was closely monitored throughout the interim time. With a lower cost per delineator and a 100% survival rate, it was found that the Peel-n-Stick delineator outperformed the other adhesives.

In summary, the goal of this research was to provide valuable input for the improvement of the existing PENNDOT standard for concrete median barrier delineation, particularly as it relates to poor visibility conditions and adhesives. In addition, it will be of value to other state DOTs encountering similar problems.

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