A movable concrete safety-shape barrier was proposed for use in a reversible-lane configuration on the Tappan Zee Bridge of the New York State Thruway. Previous tests had indicated that this barrier provides performance comparable to that of standard rigid-concrete safety-shape barrier, except for deflecting laterally on impact. Because of the narrow median width on this structure, concern arose that an impact on this barrier might cause it to deflect into opposing traffic, causing interference with another vehicle. This paper describes a model developed to assess the risk of interference collisions. Traffic and geometric conditions on the structure and the barrier's deflection characteristics were used to calculate the probability that a primary impact on the barrier would result in interference with opposing traffic. The model was programmed on a microcomputer spreadsheet to facilitate examination of various input parameters. For the conditions examined, the risk of interference impacts with opposing traffic is low, even though the barrier deflects into the adjacent lane for some impacts. This low risk can be weighed against the benefits anticipated from use of the movable barrier to determine whether its introduction is justified.
Abstract