Reducing Traffic Speed within Open Road Roadwork Sites using Obtrusive Perceptual COUNTERMEASURES Jesse A. Allpress & Louis S Leland, Jr Abstract Excessive speed is the primary contributory factor to traffic accidents within New Zealand roadwork sites. Two novel interventions designed to control traffic speed within an open road, roadwork site where drivers were required to decrease their speed from 100km/h to 50km/h were evaluated. Interventions were placed at the entrance to the work site and required drivers to pass between a 3.5 meter wide passage of either evenly or decreasingly spaced cones. Both were highly effective at reducing vehicle speed. The greatest initial decrease in speed was 9.46km/h below baseline for the decreasing spacing. Both arrangements more than halved the proportion of ‘dangerous’ speeders travelling faster than 20km/h over the speed limit. Introduction One common perceptual countermeasure is lane-width reduction. Perceptual lane-width reduction is often achieved by painting the road surface (e.g., Godley, Triggs, & Fildes, 2004), or by restricting the amount of usable road through the use of road edge rumble strips Another perceptual countermeasure is the use of transverse lines to induce the feeling of increased or excessive speed. Babbage and Leland (2005) found that if cones were used, arranging them in parallel rows produced the greatest reduction in mean vehicle speeds Debate centres around two related – but different – hypothesised mechanisms. Rutley’s (1975) increasing line progression hypothesis assumes that drivers’ perception of speed is based on the rate at which objects move through peripheral vision. Shinar (1978) and Triggs (1986) suggested that our perceptual system is most sensitive to the mere presence or absence of stimuli, rather than the rate at which those stimuli are streaming through vision. Figure 2. Figure 3. Mean speed at each counter for each condition Method Participants: approximately 25,200 motorists, 4000 trucks and 21,200 cars or smaller. Only vehicles with a headway time (the time between the vehicle of interest and the vehicle directly preceding it) of 5 seconds or greater were included in the analyses. Setting: The location was a Level 1 (>10,000 vehicles per day) highway with a normal-operation speed limit of 100km/h. The speed limit within the worksite was reduced to 50km/h. Cone interventions were set up and data recorded only in the lane adjoining the shoulder on which work was being conducted. Figure 1. Worksite Apparatus: Three traffic-counting devices were used in the experiment. Counter one was installed 400m before the first temporary speed restriction sign. and measured vehicle speeds when drivers were at open-road speeds and could not directly see the work site. Counter two was at the start of the roadwork site, 75m after the initial 50km/h speed restriction sign, and directly after the cone arrangements when they were in place. Counter three was in the centre of the work site, approximately 150m after counter two. Note: We drive on the left in New Zealand. A total of sixteen frangible fluorescent-orange road cones were used in parallel rows of eight for each intervention. Each cone was 0.9m high and had a 0.4m by 0.4m square base. Design: A multi-element baseline design, consisting of an even condition, an uneven condition and a baseline condition (randomly alternated by days), was employed. Procedure: Cones were spaced depending on the condition: for even cones, two rows of eight cones were arranged at 2m intervals (as measured from the front of the first cone to the front of the second cone); for uneven cones, the spacing between cones decreased in 0.5m increments as drivers passed through them. The longitudinal distance distance between cones in the uneven condition was therefore 3.5m at the entry point of the arrangement and 0.5m at the exit point. For both even and uneven arrangements, the lateral distance between rows of cones was 3.5m. Both arrangements can be seen in Figure 2. Figure 2. Cone arrangements Results Mean speed at each counter for each condition can be seen in Table 1 and Figure 3 Table 1. Mean Vehicle Speeds (Km/h) for Each Condition at Each Counter Counter 1Counter 2Counter 3 Even Uneven Baseline One way ANOVAs at each counter showed both the Uneven and Even traffic to be moving significantly (p<.0001) more slowly than the Corresponding Baseline data. Proportion of speeders at each counter: In addition to mean speeds, we tested whether, at each counter, a difference existed between conditions in the proportion of vehicles travelling at, or in excess of, 20km/h above the posted speed limit. The percentages of speeding vehicles can be seen in Figure 4. Figure 4. Proportion of speeding vehicles for each condition Chi Sq analyses of the proportions of speeders at each counter showed no differences at counter 1 and significantly (p<.001)more speeders in the Baseline condition at Counters 2 & 3. Discussion and Conclusions Speeding at worksites can be both significantly and meaningfully decreased by using rows of parallel cones that perceptually narrow the roadway. The proportion of dangerous speeders in the baseline (48.26%) was significantly greater – by a factor of appx. two – than in both the even (23.47%) and uneven (21.42%) conditions (Ctr2). This differential was (roughly) sustained at Ctr 3.