Movable Concrete Median Barrier: Risk Analysis of Deflection into Opposing Traffic

摘要

A movable concrete safety-shape barrier has been proposed for use in a reversible-lane configuration on the Tappan Zee Bridge of the New York State Thruway. Previous tests indicate that this barrier provides performance comparable to standard rigid-concrete safety-shape barriers, except for deflecting laterally on impact. Because of the narrow median width on the structure, concern arose that an impact on it might cause it to deflect into opposing traffic, causing interference with another vehicle. The report concerns 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, risk of interference impacts with opposing traffic is low, even though the barrier deflects into the adjacent lane for some impacts. The low risk can be compared to the benefits anticipated from use of the movable barrier, to determine whether its introduction is justified.