The AASHTO Manual for Assessing Safety Hardware (MASH) and NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, contain 6 test levels for evaluating the safety performance of longitudinal barriers, including bridge rails. When NCHRP Report 350 procedures were adopted by the FHWA, the criteria for evaluating bridge rails that was contained in the AASHTO Guide Specification for Bridge Railings (1989) were superseded. However, there is currently no specific guidance on when to use the different test levels of bridge rails. In addition, the AASHTO LRFD Bridge Design Specification contains additional criteria for the height of the railings that may unnecessarily limit the selection of tested bridge railings.
There is a need for nationally recognized guidelines in order to promote consistency among the states. For example, many states use TL-4 railings while others use TL-3 railings as their standard for high-speed highways. The use of Test Levels 5 and 6 railings is at the discretion of the states, usually in locations with heavy truck traffic and an increased potential for ran-off-road crashes (such as on curves). There is also very little guidance concerning the use of TL-2 railings on lower speed facilities.
The objective of this project was to develop recommended guidelines for the selection of Test Levels 2 through 5 bridge rails considering in-service performance.
Status: Research is complete. The final report is available as Web-Only Document 307 at https://www.trb.org/Publications/Blurbs/182548.aspx.