Effect of truck speed on the response of flexible pavement systems to traffic loading

The road network in South Africa, particularly in urban areas, is experiencing a steady increase in traffic volumes and congestion. Speed has a significant effect on the response of flexible pavement systems to traffic loading. Truck tyre loads are more often analysed as a static load in order to simplify the computations, although in reality the pavement system is subjected to a dynamic load. This paper investigates the influence of truck speed on flexible pavement system response to moving traffic loading. A truck with standard axle loads was used to conduct runs at controlled speeds and wander over a full-scale instrumented pavement test sections on road R104 east of Pretoria. The findings of this research indicate that pavement deflections increase exponentially as the truck speeds reduce to speeds below 30 km/h. Furthermore, deflections decrease marginally as the truck speeds increase to speeds greater than 40 km/h. Different flexible pavement systems present different exponential factors that reflect differences in sensitivity of the pavement systems to changes in truck speed. It is thus essential to introduce adjustment factors to deflection measurements done at different truck speeds on different pavement systems in order to compare such deflection data.