Citation

Davis DI. Transp. Res. Rec. 1979; 737: 59-60.

Copyright

(Copyright © 1979, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

An objective approach toward the development of geometric design standards has long been sought. Such an approach should link design variables to user benefits and impacts and should include economic considerations. While the relationship between shoulder design and highway safety has been extensively studied, an objective design approach has yet to be developed. The approach outlined in this paper uses traffic volume as a measure of user exposure, traffic speed as a measure of user risk, and 1975 dollars as a common economic factor to measure costs, benefits, and eventually the net worth of shoulder improvements. The approach, is based on relationships between accident rate and shoulder width that are drawn from the literature. These relationships appear to remain consistent among various independent studies and are generally supported by the conclusions of numerous before-and-after evaluations of shoulder improvement projects conducted in various states during the last few years. The relationships were developed by R. W. Sanderson in 1977. These relationships can be converted directly into a format that illustrates for given traffic volumes how many accidents can be expected to be prevented as shoulder widths increase. Plotted in this fashion, sample data show that the first 1 m (3 ft) of width over 0.6 m (2 ft) prevents the greatest number of accidents; additional width prevents diminishing numbers of accidents.