This paper presents information on analysing vehicle speeds on grades up to 10% recorded on rural highways in New Zealand. On steep upgrades, the analyses showed that vehicles adopted a constant used power level - using a mechanistic model, distributions were prepared of the used power for the representative vehicle classes. On downgrades, the analyses showed that vehicles maintained their speed or increased it. It was found that there was a relationship between used power and gradient - linear equations were developed for predicting the mean and standard deviation of the used power as a function of gradient. A simulation program was written to predict the speed of any vehicle type travelling along an upgrade or a downgrade. The speeds predicted compared very favourably with the database observed speeds. Two examples are given of a speed-distance profiles from the model which are particularly useful for economic appraisal purposes. (A)
Samenvatting