38-41 Hammond Feature

ITE JOURNAL / AUGUST 2001 BACKGROUND High speeds and rapidly increasing vehicle volumes characterize many of America’s rural, two-lane highways. These features, combined with midto shortradius horizontal curves and limited sight distances, can create hazardous road conditions for the motoring public. These highways may or may not exhibit high accident numbers or rates but are often described by local road users as dangerous due to near misses or other negative experiences. Problems often occur on stretches characterized by yellow solid double-line striping on which no passing is allowed in either direction. In negotiating sudden and/or sharp horizontal curves, vehicles on the outside of the curve tend to encroach upon the opposing travel lane. Roadway features or conditions such as poor striping visibility, narrow lanes, limited shoulder width, roadside hazards and wet or polished pavement tend to compound the likelihood and severity of these crashes. The implementation of a simple control measure to encourage speed reduction on the curve and less lane encroachment is a much-needed safety improvement for many rural two-lane, two-way roads. Motorist behavior was observed upon encountering midto short-radius curves that are less than 500 feet (ft.) [150 meters (m)] where sight distance is limited. More specifically, driver reaction to two variations on the use of raised pavement markers (RPMs) as a control measure was noted and evaluated by changes in vehicle speed and encroachment distance on the curve. In the review of pertinent literature, hazardous horizontal curves were improved by the application of additional delineation. Traditionally, these marking systems have been used in advance of the curve to provide ample warning to the motorist who may not be aware of the changing alignment. Also, delineation at the curve location with retro-reflective RPMs has been used to increase the nighttime visibility of the changing alignment. Research by AlMasaeid and Sinha1 successfully correlated the application of painted roadway markings with a 14 percent accident reduction factor at accident-prone locations. Earlier studies by Pigman and Agent2 and Stimpson3 suggested significant decreases in vehicle speed and opposing lane encroachment after applications of the RPM. Islam4 found that many characteristics of the driver-vehicle system combine to create a hazardous location, though possibly none more than the changes in operating speed and travel path that occur as the vehicle navigates the curve. Three specific research variables were used to characterize the relationship between RPM application and driver behavior. The following data were collected to quantify this relationship: • Measured encroachment distance before and after the installation of RPMs at a 40-ft. (12-m) spacing; • Measured encroachment distance after the installation of additional RPMs creating a 20-ft. (6-m) spacing; and • Average operating speeds throughout the length of the curve before and after the RPM applications.