POST-MOUNTED DELINEATORS AND RAISED PAVEMENT MARKERS: THEIR EFFECT ON VEHICLE OPERATIONS AT HORIZONTAL CURVES ON TWO-LANE RURAL HIGHWAYS

Post-mounted delineators (PMDs) and retroreflective raised pavement markers (RPMs), either individually or in combination, have been recommended in previous research as supplemental delineation treatments at horizontal curves on two-lane rural highways. However, these recommendations have been based on limited amounts of operational data or accident models that show little correlation between accident rates and the type of delineation treatment. No attention has been paid to the short-term effects of changing from one delineation treatment to another or to the long-term operational effectiveness of the treatments. To evaluate how vehicle operations changed, existing PMDs were removed and replaced with RPMs supplementing the existing painted centerline at five horizontal curves on two-lane rural highways in Texas. Vehicle operations were monitored on the outside lane of the curves first with the existing PMDs in place and then with the RPMs after 1 day (short-term), 6 to 11 weeks (intermediate-term), and 11 months (long-term). Operational measures of effectiveness that have been suggested by previous research to be correlated to accident experience were evaluated, including the speed at the midpoint of the curve, speed change from the beginning to midpoint of the curve, lateral placement at the midpoint of the curve, and number of vehicle encroachments into the opposing lane at the midpoint of the curve. Vehicle operations with the RPMs compared favorably with the existing PMDs in both short-term and intermediate-term evaluations. The long-term evaluation at one curve indicated that the RPMs, which had lost most of their reflectivity, continued to provide adequate near delineation, but that their far delineation was somewhat degraded.