The current AASHTO Specification provides designers with static design criteria and/or crash test criteria to qualify a bridge railing system. Accordingly, a bridge railing system meeting the AASHTO specifications is used on any bridge regardless of vehicle mix, traffic volume, and speed and bridge geometry. The Multiple Service Levels Approach (MSLA) procedure for selecting bridge railings is a new approach differing markedly from traditional practice. The objective of the MSLA is to provide a level of motorist protection consistent with the degree of traffic hazards present at a highway site. With the MSLA, the degree of risk is the combined measurement of the probability of an impact occurrence, the probability of collision severity and the consequences of that impact occurrence. Accordingly, the procedures described in this paper consider encroachment rates, traffic volume, vehicle mix, category speed, shoulder widths, and horizontal alignment as these factors relate to probability of an impact occurring and the severity probability of the impacts. Using a collision severity index as an indicator of bridge railing performance requirements, six service levels were established. By setting critical impacts corresponding to a uniform probability factor, service level requirements are determined for a site. Thus, using the MSLA procedures, a designer selects a higher service level device at locations where collisions are numerous and severe; and lower service level devices are indicated for the relatively safe or improbable accident locations. Since the higher service devices are generally more costly to construct, highway safety funds can be more wisely expended by selecting the service leve1 appropriate for each location.

The current AASHTO (l, 2) specification provides designers with static design criteria and/or crash test criteria to qualify a bridge railing system. Accordingly, a bridge railing system meeting the AASHTO specifications is used on any bridge regardless of vehicle mix, traffic volume, and speed and bridge geometry. Although not specifically stated, the AASHTO static/elastic design criteria are directed to the passenger-size vehicle with no