CR182: Perceptual Countermeasures: Experimental Research (1999)
Speeding has long been recognised as a major factor in road crashes in Australia that deserves priority attention. While police enforcement quite rightly has been the major weapon against excessive speeding, there have been a number of calls for supplementary measures to reduce speed related road trauma.
A review of the research and action needs in speed management was undertaken in 1994 that highlighted low cost perceptual countermeasures (PCMs) as a priority research issue. Following the review, a collaborative research program commenced for the ATSB Road Safety and the Roads and Traffic Authority of New South Wales. The Monash University Accident Research Centre (MUARC) in conjunction with ARRB Transport Research has undertaken the research.
Earlier published reports have included a literature review (CR 4/94), and a validation study of the driving simulator at MUARC (CR 169). This report describes the results of a series of simulator studies that systematically tested a number of PCMs using licensed drivers in the MUARC driving simulator.
On-road testing of new treatments can be problematic if they have not been shown to be a benefit first in an off-road test environment. A driving simulator is an ideal test environment as it provides a safe, inexpensive and ethical facility to address these issues.
The driving simulator at MUARC was developed by the Transport Accident Commission using the latest silicon graphics projections and provides a 180 degree front view as well as a rear image. The simulator also provides "road feel" through three positive feedback dampers under the car and a quadraphonic sound system. From earlier work, the simulator had been shown to be a valid test environment for evaluating PCMs.
A number of participants were recruited to "drive" the simulator and a total of seven human factor experiments were conducted to test systematically a range of PCMs, including:
- Transverse road markings;
- Lane edge & herringbone treatments;
- The Drenthe province treatment from the Netherlands;
- Centreline and other edgeline treatments; and
- Several enhanced curvature treatments.
Drivers drove a series of test tracks which had previously been programmed to include similar treated and untreated road locations. Speed and lateral position measures were compared at both the treated and untreated locations. Differences were tested statistically to demonstrate significance using Analysis of Variance techniques.
Transverse lines are high contrast, painted or thermo-plastic strips about 60cm wide that are placed across the driving lane for up to 400m on the approach to an intersection or hazard. They are generally spaced at decreasing spacings in the direction of travel.
The results from this study showed that transverse lines can be effective at reducing travel speed by up to 11 km/h, both immediately after entering the treatment zone (suggesting an alerting effect) as well as throughout the treatment area (consistent with a perceptual effect). However, it did not seem to matter if the transverse lines were at decreasing or constant spacings.
A half Wundt Illusion treatment (forward facing chevrons across the lane) had little effect on travel speed compared to transverse lines.
Lane Edge & Herringbone Treatment
Peripheral transverse lines (approximately 60cm from the lane edge) also resulted in significant speed reductions on the approach to an intersection, although not as large as the full-width lane lines.
A herringbone pavement marking system with decreasing line frequency had been previously suggested as a PCM to speeding in the lead-up to a road hazard. This was a variation of peripheral transverse lines angled at approximately 45deg to the edgeline that can be placed either pointing towards the approaching vehicle or away from it.
The results showed some speed reductions for herringbone edgeline treatments, similar to those for the peripheral transverse lines above. In addition, it did not seem to matter if these lines were perpendicular to the edge of the road or slanted either towards or away from the driver.
A novel tree planting alongside the road at diminishing spacings had no effect on travel speed.
The Drenthe Province Treatment
This treatment was first developed in the Netherlands and has been used there to counter speeding on 80 km/h rural highways.
The standard version comprises a gravel centreline (with while intermittent strips) as well as intermittent gravel edgeline treatments and provides 2.25m of free road surface between these treatments. Variations of the Drenthe treatment examined here included white painted edgeline treatments (no gravel) and solid gravel edgeline treatment.
The results showed that only the standard Drenthe treatment elicited significant speed reductions of up to 2 km/h but did cause vehicles to move 16 cm closer to oncoming traffic. Other variations failed to produce significant speed reductions.
Centreline and Edgeline Treatments
The next series of tests examined the effectiveness of novel median treatments (white gravel and white hatching) and two edgeline treatments (a chequered pattern and low contrast intermittent gravel edgelines. These treatments are intended to be used for long stretches of road as a speed countermeasure.
Hatched median strips were successful in reducing travel speed by 3 km/h. In conjunction with a low visual contrast gravel edgeline, it further reduced speeds by 3 km/h. These speed reductions only occurred on straight road sections. The chequered edgeline and gravel median, however, did not influence travel speeds.
Narrow lanes (below 3 metres) also produced significant speed reductions, although the traffic mix would need to be taken into account when choosing this treatment.
Previous research has suggested that some road curves are hazardous because they are perceived by drivers to be less curved than they really are. Thus, low cost PCM treatments for these hazardous curves need to correct this illusion by over-stating the amount of curvature. Examples include enhanced edge and centreline lines or roadside posts (both constant height and ascending patterns) that suggest a sharper curve.
The results showed that edgeline enhancements actually led to higher travel speeds and tended to shift the vehicle closer towards the centreline. An enhanced centreline, on the other hand, resulted in no significant changes in travel speeds and lateral position.
An enhanced post layout on the outside of the curve only was the best post configuration in terms of reduced travel speed for left curves. An enhanced post layout on the outside of the curve with ascending post heights led to less speed reduction on the left curve than the non-ascending posts, but also led to a speed reduction on the right curve. Post spacing treatments generally had little effect on the lateral position of the vehicle.
A number of these PCMs appeared effective at reducing travel speed, including:
- Full-width transverse lines;
- Peripheral transverse lines and lane edge herringbone treatments;
- Hatched median (especially with a lane width narrower than 3 metres), with or without intermittent gravel edgelines;
- Enhanced post spacings (possibly with ascending heights) for road curves.
It was noted that the effects of these treatments need to be further evaluated on the road to demonstrate finally the speed reduction benefits, both immediate and longer-term, as well as their safety benefits.
A number of recommendations for further research are listed in the report, including a cost-benefit analysis of promising treatments and examination of other PCM treatments that might be applicable.
Download Complete Document: Percept_Res [PDF: 1695 KB]
Type: Research and Analysis Report
Sub Type: Consultant Report
Author(s): Stuart Godley, Brian Fildes, Thomas Triggs & Lorraine Brown
Topics: Road, Speed
Publication Date: 01/11/99