Improvement to Black Spot Treatment Strategy

Monash University Accident Research Centre - Report #132 - 1998

Authors: A. Duarte & B. Corben

Abstract

Various evaluations of Victoria's accident 'black spot' programs have each shown highly cost-effective performance overall, and for several treatment types in particular. However, not all treatment types have been successful.

This project identified five treatment types which had not shown the intended effect, because crashes either increased or showed no appreciable reduction in the period after treatment implementation. The five treatment types investigated were pedestrian facilities, bridge guard rail treatments, street lighting improvements, skid resistance treatments and the erection of traffic signal mast arms. The study aimed to improve the effectiveness of these treatment types; to identify black spot location types which warrant a more concerted effort being directed towards countermeasure development; and to refine black spot identification procedures to enhance future programs.

The study found that there is scope for improving program development processes through a more rigorous application of procedures for identifying black spot locations and choosing more comprehensive treatments to address crash problems. Improvements to evaluation processes have also been identified.

Opportunities to increase the effectiveness of pedestrian operated signals, flush median treatments, skid resistance treatments, traffic signal mast arms and bridge guard rail treatments have been recommended. Further, street lighting has been identified as being successful in reducing night to day crash ratios.

The strategic and detailed improvements suggested by this report aim to improve the effectiveness of future black spot programs.

Executive Summary

Various evaluations of Victoria's accident 'black spot' programs have shown highly cost-effective performance overall, and for several treatment types in particular. Notwithstanding the very good overall performance of these programs, not all treatment types have been successful. This project identified, out of a total of 43 treatment types comprising the 1992/94 and 1994/96 Transport Accident Commission's (TAC) Black Spot Program, five treatment types which had not shown the intended effect, because crashes either increased or showed no appreciable reduction in the period after their implementation. The treatment types were pedestrian facilities, bridge guard rail treatments, street lighting improvements, skid resistance treatments and the erection of traffic signal mast arms.

The specific objectives of this study were to improve the effectiveness of these treatment types; to identify black spot types and location types which warrant a more concerted effort being directed towards countermeasure development; and to refine black spot identification procedures so that overall performance of future programs will be enhanced.

Study Method

Data used to evaluate the 1992/94 TAC Black Spot Program were updated and combined with corresponding 1994/96 data. Crash reduction estimates were recalculated using a quasi-experimental design with control groups, and an Odds Ratio analysis, which aggregated treatments of like-type. This study examined some 75 individual treatments belonging to one of the five types mentioned above. Investigations have led to the following main findings.

Main Findings

This study found that, of the 75 treatments investigated, 34% were not black spot sites in the before-period, 30% were black spot sites that were successfully treated and 36% were black spot sites where the treatment did not have the desired effect.

1. There is scope to improve program development processes through:

more rigorous and systematic application of procedures for identifying black spot locations for possible treatment. For example, treating routes whose night/day crash ratios are significantly above the corresponding state average is more likely to identify locations where street lighting improvements are needed and where real crash reductions can occur. Similarly, treating bridges with a history of crashes into end-posts or other structural elements will lead to more effective guard-rail treatment programs.
improved methods for analysing crash problems at individual locations to ensure that the most appropriate treatment type is chosen and that chosen treatments comprehensively address the predominant crash types.

The study also suggests a number of refinements to black spot identification procedures to enhance overall performance of future programs.

2. There is scope to improve program evaluation processes through:

more accurate data retrieval methods to ensure relevant crash data are used in evaluations.
evaluation of treatment effectiveness in terms of target crash type.

3. Treatment effectiveness can improved by:

Pedestrian Facilities

comprehensive targeting of crash problems, and not relying on "spot" treatments alone to address crash problems occurring along a route. Cost-effectiveness can also be improved by treating locations where high numbers of pedestrian crashes have clustered.
installing pedestrian operated signals, together with other countermeasures, such as continuous fencing, raised medians, measures to moderate vehicle speeds and signal enhancements to foster greater use and compliance by pedestrians.
providing raised medians along routes with high levels of pedestrian activity. Where flush medians are provided, start and end points should be clearly delineated by raised traffic islands, and medians painted or otherwise surfaced to clearly differentiated from traffic lanes. However, the use of flush medians should be avoided, or at least minimised, in areas of high conflict between pedestrians and turning vehicles.

Bridge Guard Rail

implementing proven, comprehensive treatments for entire road segments. Treatments may include shoulder sealing, and improvements to curve alignment and delineation.

Skid Resistance

providing additional measures to moderate vehicle speeds before entering horizontal curves with less than the desired minimum radii for the posted speed limit. Subject to cost-effectiveness assessment, re-design and re-construction should be considered, with special attention to curve radii, super-elevation, shoulder sealing and improved surface drainage.
design and use of improved pavement surface materials.

Mast Arms

specifying quartz halogen lanterns to increase the conspicuity of signal displays. Where sight distances to signals is severely limited, mast arms can be accompanied by static or flashing advance warning signs. Signal maintenance strategies should assign high priority to traffic signal mast arms at black spot locations.

4. Other Black Spot Identification Issues

Typical locations which warrant a more concerted effort being directed towards countermeasure development include:

routes with a high pedestrian crash frequencies e.g. strip shopping centres
rural black lengths with a run-off-the-road problem, together with hazardous bridges or culverts within the road length.

Sponsoring Organisation: Baseline Research Program - Department of Justice, Transport Accident Commission, Royal Automobile Club of Victoria (RACV) Ltd, VicRoads