Downgrade Speed Characteristics of Heavy Vehicles

The speed characteristics of heavy vehicles on downgrades are analysed. The analyses were made by field observations of truck speeds on six rural two-lane downgrades. Loaded trucks considerably reduced their speeds at the beginning of a downgrade. The amount of reduction, termed the approach-speed gradient, was related to the length and slope of the downgrade, the second variable contributing exponentially to the increase in gradient. Buses and empty trucks increased their speeds at the downgrades studied. Using a previously developed model, which is based on delay measures and the speed distribution of trucks and passenger cars, passenger-car equivalents for downgrades are calculated and evaluated.