Speed has often been cited as a critical factor which affects safety on urban local roads. Sometimes geometric features are designed as slow points to control speed on urban local roads. This paper discusses the effectiveness of one type of slow point, the 90 degree bend. To determine the effectiveness of the 90 degree bend in controlling speed, surveyed speeds were compared with expected speeds based on design codes. Speed surveys of eleven 90 degree bends in urban local roads were conducted in three municipalities in Melbourne. The Vehicle Data Acquisition System (VDAS) was used for these surveys. This paper describes vehicle speeds under various physical conditions such as road widths, traffic volumes, radius of curvatures and street lengths at these 90 degree bends. The results showed that although 90 degree bends do control speeds, they are more likely to be effective in controlling them to around 25 km/h rather than 20 km/h as suggested in the design codes. If the design parameters are flawed on this key component, and the lengths of urban roads were designed according to designcodes' recommendations, the implication is that it is possible that at some time in the future, traffic managers may be required to introduce LATM to curb speeding vehicles. (A)
Abstract