PERFORMANCE LEVEL 2 BRIDGE RAILINGS

The highway profession is in the process of upgrading performance of bridge railing systems. In 1989 the American Association of State Highway and Transportation Officials adopted the Guide Specifications for Bridge Railings. That document addresses bridge railing systems for three levels of performance. Proof of performance should be demonstrated by full-scale crash tests set forth in that guide, and there is a general trend toward full-scale crash testing of new highway safety hardware in the highway industry. Performance level selection procedures included in the guide indicate that a performance level 2 (PL 2) railing is needed on many new bridge structures. This level has a strength test with an 18,000-lb single-unit truck striking the railing at 50 mph and at a 15-degree angle. The specified height of the center of gravity of the test truck is 49 in. Other tests with smaller vehicles are also required of a PL 2 railing. Four railing designs have been tested in a continuing pooled-funds study involving 23 states, the District of Columbia, and the Federal Highway Administration. The railings included one steel beam-and-post design and three concrete parapet designs. Performance of these railings in full-scale tests indicates that they are all acceptable for PL 2 of the 1989 guide specifications. All railings were sufficiently strong that no structural distress was observed except in the bolted rail-to-post connections in the metal railing. In all tests except one, vehicles were contained and redirected with reasonably good stability in roll and tracking with small exit angles and acceptable collision severity values. The exception was the 18,000-lb truck test on the New Jersey safety shape concrete parapet. In this test the vehicle finally rolled onto its side (away from the railing). This is considered acceptable behavior.