Citation

Michie JD. Transp. Res. Rec. 1980; 757: 17-22.

Copyright

(Copyright © 1980, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

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Abstract

In order to upgrade traffic safety of existing bridges in a systematic and cost-effective manner, we must have a clear understanding of how safety is measured and controlled. Safety is not an absolute but a relative condition that balances the risk of an event and society's acceptance of that risk. Something is considered safe if its risks are acceptable. Risk is measured by the probability of the occurrence of an adverse event (i.e., bridge accident) and the event's consequences (i.e., collison severity). Based on length alone, a bridge is 50 times more hazardous than the roadway in general. The large number of bridge accidents is attributed to narrow bridges and to obsolete approach guardrail and bridge rail installations. To improve bridge traffic safety, the ideal solution would be to widen all narrow bridges and upgrade barrier installations on all other bridges. Because of cost, this approach is not practical. As an alterative, bridge selection for safety improvement can be based on degree of risk and available funds concentrated on the high-risk bridges. This procedure, which is also applicable to other roadside safety problems, advocates uniform standards for degree of risk rather than uniform standards for design. In fact, design standards will be varied according to site requirements to achieve the acceptable level of risk. Two techniques are presented to identify bridges that have a high degree of risk: (a) adverse accident experience and (b) high traffic volume coupled with substandard highway features. The extent and type of safety improvements are presented.