Organisation: Douglas Stewart Online
Date uploaded: 11th April 2013
Date published/launched: Pre 2009
Three acute, accident prone bends were converted from transitional to circular alignment. Comparing equal before and after periods, acidents have been reduced significantly, by about 80%, and cost effectiveness has also been high.
Investigation of ‘safe’ and ‘hazardous’ bends had indicated that the main difference between them was not whether their curvature was large or small, but whether it was constant or variable. This led to the hypothesis that drivers have more difficulty in perceiving the curvature of a transitional bend, because it can deceive them into maintaining an excessive speed.
Three acute, accident prone bends were therefore converted from transitional to circular alignment. Comparing equal before and after periods, acidents have been reduced significantly, by about 80%, and cost effectiveness has also been high. These results suggest that widespread prevention of accidents at sub-standard bends would be simple and inexpensive, and that design codes should no longer recommend the use of transition curves.
It is proposed that accident migration could be countered by selected retention of sub-standard bends.
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Doug Stewart