Speeding has been long recognised as a major factor in the occurrence and severity of road crashes. While enforcement, education/publicity and engineering programs have assisted in reducing speed-related road trauma, supplementary measures to reduce the incidence of unsafe speed behaviours, particularly at hazardous locations, have been sought.
A study was undertaken by Fildes and Lee in 1993 to assess needs for further research and action to reduce excessive speeding. A key outcome of the study, which involved leading experts across Australia, was the need to develop low cost perceptual countermeasures designed to reduce driver speed on roads.
Perceptual countermeasures (PCMs) against excessive speeding refer to manipulations of the road scene presented to a driver that can influence his or her subsequent behaviour. For the most part, these treatments tend to be relatively low cost additions or modifications to the road or roadside setting that can lead to a change in the way the driving environment is perceived by drivers.
The then Federal Office of Road Safety (now Australian Transport Safety Bureau) and the Road and Traffic Authority of New South Wales (RTA NSW) commissioned the Monash University Accident Research Centre (MUARC) and ARRB Transport Research (ARRB TR) to conduct a long-term study of perceptual countermeasure designs and likely effectiveness. A four-phase research program commenced in 1993.
The first stage was a literature review of perceptual countermeasures by Fildes and Jarvis (1994). The second stage of the project was a simulation validation study (Fildes, Godley, Triggs & Jarvis 1997).
The third stage of the project involved the evaluation of a range of PCMs using the driving simulator at MUARC. It was recommended that the effects of the promising treatments from this research be further evaluated on the road to demonstrate the speed reduction benefits, both immediate and longer-term, as well as their safety benefit.
The fourth and final stage of the study (the current stage) involved applying two of the more promising PCM treatments on a sample of mid-block and intersection locations and evaluating their effectiveness and cost-benefits. This report documents the on-road evaluation of two PCM treatments: peripheral transverse lines applied on the approach to intersections and enhanced post spacings with ascending heights applied at road curves.
The treatments were applied at six intersections and six curve sites in Melbourne and Sydney. The evaluation study comprised before and after observations of vehicle braking distance, lateral displacement, and speed profile at the treated sites, and then compared these observations and measurements to sites of similar geometric and geographic characteristics which were untreated (i.e. control sites).
The comparison of data enabled the effects of each treatment to be evaluated, both before and after installation, while controlling for traffic differences at the sites. The inclusion of two after evaluation periods at 1-2 months and 12 months after installation allowed the short- and long-term effects to be evaluated separately.
At both the curve and intersection treatment sites, the results indicate that the treatments were not uniformly effective at reducing travel speeds, although the long-term results were more promising than the short-term findings. Reductions in average speeds were observed more consistently at intersection sites than at curve sites.
At the curve sites, the treatment effects immediately after installation were quite mixed, with only two of the six treated sites recording significant speed reductions relative to control sites.
In the longer-term, the PCMs produced relative speed reductions at three of the six sites, and had no effect at two sites. At the other treatment site, road condition changes and damage to the treatment during the study period made the results unreliable.
It was noted that the two sites that demonstrated no effect were better delineated by guideposts than the other sites prior to treatment installation. That is, the treatment appears to have been more effective at sites, which were not delineated, or not well delineated, by guideposts prior to treatment installation. Furthermore, one site was a flatter curve than the others and drivers did not need to slow down much to negotiate it, possibly contributing to its lack of effectiveness.
At the intersection sites, the PCMs had more effect on reducing travel speed, relative to the control sites, both short-term and long-term. Speed reductions were observed at a majority of the locations.
An analysis of segment differences between treated and control sites was only partially successful, due to missing data. However, where comparisons were possible, treated intersections showed differences in the speed profile in the approach to the intersection. The results also suggest that while this treatment was expected to have its greatest effect on vehicle speeds in the early stages of the treatment, it is possible that speed reduction effects occurred over the second 200m of the treatment prior to the intersection.
The analysis of braking behaviour and lateral vehicle positioning did not demonstrate any effect of the perceptual treatments at intersections.
The NSW curve and intersection control sites generally demonstrated an increase in average vehicle speed over the long-term study period. Average vehicle speeds increased at four of the six control sites, with no significant changes at the other two control sites. It has not been possible to establish whether or not this was a general trend in NSW over the study period. The treatment sites, on the other hand, all demonstrated no significant change in average vehicle speed over the long-term study period. If there was an overall increasing trend in vehicle speeds in NSW during the study period, it appears that the treatments may have been successful in diminishing the effect at the treatment sites.
Given that the PCMs tended to be more effective in the long-term, it might suggest that drivers need time to accommodate to them and change their driving behaviour. It is noted that, at all of the sites, the majority of traffic was local and most drivers would probably be very familiar with the road.
In light of these results, a number of recommendations might be worthy of consideration.
- For sites that demonstrated a positive long-term effect, conduct further speed surveys approximately 2 years after installation of the treatments, to determine whether the speed reduction effects have been sustained.
- If further surveys of the intersection treatment are to be conducted, then there is a need to record and analyse speed measurements over the entire length of treatment (which would require more than one speed laser gun).
- Compare the detailed results of this study with the previous simulation study (Godley, Fildes, Triggs & Brown, 1999) to determine the differences in actual results and simulator results.
- Identify other perceptual countermeasures, from the previous studies, that could be trialled.
- Further research is warranted targeting locations of high traffic exposure and crashes in urban shopping precincts and school and residential zones. Research needs to evaluate speed reductions as well as crash savings.
Type: Research and Analysis Report
Sub Type: Consultant Report
Author(s): Macaulay J, Gunatillake T, Tziotis M, Fildes B, Corben B, Newstead S
ISBN: 0 642 25521 0
Topics: Road, Speed
Publication Date: 01/01/04