Benefit/cost Analysis of Road Trauma Countermeasures: rural road and traffic engineering programs

Monash University Accident Research Centre - Report #34 - 1992

Author: K. Ogden

Abstract:

This report represents the results of a study which examined the safety effect of providing sealed shoulders, overtaking lanes, and edge lining on rural highways in Victoria. For shoulder sealing, a statistically significant reduction in casualty accident frequencies was found, equivalent to a 43 per cent reduction on a per vehicle kilometre basis. Comparing economic benefits and costs, a benefit/cost ratio was determined of 2.9 x (AADT in thousands), where AADT is Annual Average Daily Traffic. The study was unable to find any statistically significant effect of overtaking lanes or edge lining on accidents.

Summary

This report presents the results of a MUARC project which sought to determine the safety effect of three rural road programs, namely sealed shoulders, overtaking lanes, and edge lining.

Data were obtained on the location, condition and cost of recently installed projects in each of these activities on two lane-two way roads (i.e. one lane in each direction) in Victoria. Accident data were obtained for these sites, and a before and after comparison, using control sites, was undertaken.

Most shoulder sealing programs examined involved a low cost sealing of an existing shoulder, typically involving an interim bituminous sealing treatment, followed a year or so later with a reseal in conjunction with a pavement reseal. The shoulder width is typically between 600 and 1200 mm, with 600 or 800 mm being the most common. The results for this type of treatment indicate that:

shoulder sealing was associated with a statistically significant reduction in casualty accident frequencies at sites where it was installed on 2-lane 2-way rural highways in Victoria,
casualty accidents were reduced by 43 per cent, on a per vehicle kilometre basis, at such sites,
this is equivalent to a reduction of 0.073 casualty accidents per million vehicle kilometres,
the breakeven point (the point at which it is economically worthwhile) to install sealed shoulders is at a traffic flow of about 350 veh/d,
the benefit/cost ratio of shoulder sealing can be calculated from:

benefit/cost ratio = 2.9 x (AADT in thousands)
where AADT is Annual Average Daily Traffic

for example, if the AADT is 4,000 veh/d, a benefit/cost ration of about 11.6:1 could be expected,
the main accident reductions are in rear end, overtaking - out of control, off carriageway to left, and off carriageway to right into fixed object crashes.

The study was unable to find any statistically significant effect of overtaking lanes or edge lining on accidents. In the former case, this was mainly because of a small number of suitable sites and a short "after" period. In the latter case it was again because of a shortage of sites, and also the absence of a suitable control situation. More work in these areas is recommended.

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