Three roadside drainage features have been assessed for their effects on the handling and safety of two saloon cars. The features tested were a triangular and trapezoidal surface drainage channel, and a French Drain in an `open' and `capped' form. The vehicles, suitably instrumented, were driven into and across the features at a range of speeds and approach angles and a subjective assessment of the vehicle handling made by the driver. Computer simulations of the track test configurations were also performed. It was the intention to dispense with further expensive physical track tests if the simulation results correlated sufficiently well with the track test data. Limited testing was also conducted with a pedal cycle and a motorcycle (uninstrumented) on the triangular channel and the two forms of French Drain. The track test results revealed a clear difference in the effects on the two vehicles, but the difference in the effects of the two surface drainage channels was less obvious. However, it was considered that the concrete surface drainage channels represented an acceptable level of risk to vehicle safety and were adopted as the `benchmark' against which alternative features were assessed. The computer simulations agreed generally with the track test results; the observed differences were thought to be a result of simplifications in the vehicle dynamics algorithms. Further refinement of the computer model would have improved the correlation between the track test results and the model predictions, but this was outside of the scope of the project. It was concluded that the surface drainage channels present a distinctly different problem to that posed by the French Drain, in that the surface drainage channels induce a much larger degree of physical vehicle disturbance. Single track vehicles, which have an inherent primary instability, are affected to a greater degree than twin track vehicles and are particularly sensitive to abrupt surface transitions of a longitudinal nature. However, it was considered that, at the relatively low speeds a pedal cycle can normally attain, the concrete surface water channels posed no significant risk to cyclists. Recommendations have been proposed to minimise the risk to errant vehicles posed by road edge drainage features, including the provision of safety fencing, hard strips and raised rib road edge markings under certain circumstances. (A)
Abstract