Effectiveness of Experimental Transverse- Bar Pavement Marking as Speed-Reduction Treatment on Freeway Curves

roundabouts, intersections, bridges, and work zones. A 1995 review of current practice by Griffin and Reinhardt showed rather extensive experimentation with transverse-bar markings throughout the United States (1). Several patterns, colors, sizes, and spacings had been reported for the various transverse-bar installations, with widely inconclusive results on their effectiveness for speed reduction or safety improvements. Most of the studies reported some level of speed reduction after installation of the treatment, although they were inconclusive about whether the observed speed reductions would be sustained over the course of time. More recently, Katz et al. analyzed both the shortand longterm effects on speeds of a transverse-bar treatment installed at three horizontal curves (2). The three sites included a freewayto-freeway exit ramp in New York, a two-lane rural arterial in Mississippi, and a two-lane rural local highway in Texas. The results showed a long-term decrease in speeds at each of the sites, although the magnitude of the decrease varied by site. The freeway exit ramp saw a long-term mean speed reduction of 3.9 mph, while smaller speed reductions were observed at the rural arterial and local highway. The greater speed reduction at the freeway site was partially attributed to a greater percentage of unfamiliar drivers there compared with the other sites. Drakopoulos and Vergou evaluated the effect of a convergingchevron treatment on speeds at a single-direction freeway-to-freeway exit ramp on I-94 in Milwaukee, Wisconsin (3). A before-and-after analysis showed reductions in the mean and 85th-percentile speeds of 15 and 17 mph after the installation of the chevron markings. These changes were highly significant, both statistically and practically, considering that the after data were collected 18 months after installation of the markings and that the comparison site did not show considerable changes in speeds during the same period. No adverse effects attributable to the marking treatment were reported.