SAFETY TREATMENT OF ROADSIDE DRAINAGE STRUCTURES

The purpose of the research was to develop traffic-safe end treatments for cross-drainage and parallel-drainage structures that would not appreciably restrict water flow. Preliminary designs were first evaluated by computer simulation, by use of a test pit in which the clear open space and grate spacing could be varied, and by use of an earth berm similar in geometry to a driveway. Promising designs were then subjected to full-scale prototype testing by using both subcompact and full-sized automobiles. Finally, guidelines for implementation of designs were developed by using a cost/benefit analysis. Traffic-safe culvert end treatments can be achieved as follows. For cross-drainage structures, (a) all culvert ends not shielded by a traffic barrier should be made to match the existing side slope with no protrusion in excess of 4 in. (10.2 cm) above grade, (b) culverts with clear openings 30 in. (76.2 cm) or less need no safety treatment other than that mentioned in a, and (c) culverts with clear openings greater than 30 in. can be made traffic-safe by grate members placed on 30-in. centers oriented parallel to the flow and in the plane of the side slope. For parallel-drainage structures, (a) the roadway side slope (or ditch slope) should be 6:1 or flatter in the vicinity of the driveway, (b) the driveway slope should be 6:1 or flatter, (c) the transition between the side slope and the driveway slope should be rounded, and (d) safety treatment of the culvert opening should include an end section cut to match the driveway slope and have cross members (grates) spaced every 24 in. (61.0 cm) perpendicular to the direction of water flow. (Authors)