Retro-fitting incremental clearzone widths to existing rural roads
The aim of this paper is to outline new alternative and pragmatic incremental clearzone
widths that when retrofitted to existing high speed, undivided rural roads are expected to
have a significant effect on reducing the road toll.
Although the percentage of run off road crashes varies according to individual routes, they
usually form the major component of total road crashes on the rural road network. Run off
the road crashes on high speed, undivided rural roads cost the NSW community about $360
million per year and result in approximately 80 deaths per year. One cost-effective way to
reduce the high number of these types of crashes is to take a more pragmatic view of what is
practical and achievable in reconstructing and maintaining the existing alignments and
formations on the two lane rural road network.
Road Design Guides have tended to concentrated on ?best practice? principles for designing
?greenfield? type road projects. However, they have rarely addressed what was practical and
achievable for upgrading existing road alignments and formations. Consequently, the
application of full width clearzones of 10 metres to 12 metres are an exception on most
existing rural roads throughout NSW. The development of incremental clearzone widths is an
attempt to address this lack of design direction when confronted with what is regarded as
acceptable and affordable practice on ?brownfield? projects. It concentrates on reducing the
severity of run off road crashes into objects as the major concern and not the total elimination
of these types of crashes. It tries to achieve this by restricting the design parameters to a
practical level of maximum safety benefit return for the minimum cost of construction.
This study is consistent with the safe systems approach to road safety which accepts that
humans will make mistakes and that the road should be constructed and maintained to
ensure these errors don?t result in death or serious injury. Cost effective treatments such as
applying incremental clearzones are expected to provide good safety benefits yet be less
environmentally destructive than current ?Greenfield? clearzone standards. If they are
implemented throughout the NSW road network they will provide a more forgiving roadside
environment than presently exists along the edge of most rural roads.