HUMAN FACTORS AND SAFETY IMPACTS OF DELINEATION COUNTERMEASURES ON TWO-LANE RURAL ROADS

A conventional approach to reducing lane departure crashes is to improve path delineation, in particular on curves. Current treatments on two-lane rural highways include permanent raised pavement markers (PRPMs) and rumble strips. This paper considers the effect of these treatments on driver behaviour and on safety. Snowplowable PRPMs were shown to be associated with improved safety on high volume, high design standard roads in a recent NCHRP study. Conversely, there was a deterioration in safety (26% more nighttime crashes on low volume roads (5-15000 veh/day) with degrees of curvature >3.5 (about 500m). Based on studies of related devices, it is expected that, with snowplowable PRPMs, drivers will position themselves further from the centreline. This likely underlies the positive safety impacts found on high volume, high design standard roads. However, a second expected effect is that with improved preview of the road ahead, drivers increase speed at night. This adaptive behaviour, in combination with a lane position closer to the shoulder, likely underlies the negative safety impact found on tighter curves. Centreline rumble strips were associated with improved safety both day and night in a recent Insurance Institute for Highway Safety study. Target crashes were reduced by an average of 25%. No negative safety impacts were seen. Based on studies of related devices, it is expected that with centreline rumble strips, which provide auditory feedback of lane crossing but do not improve path delineation, drivers are likely to reduce lane encroachments but unlikely to increase speed. These effects may explain the overall positive safety impact.