COST EFFECTIVE DESIGNS FOR LOW VOLUME SEALED ROADS IN TROPICAL AND SUB TROPICAL COUNTRIES

Studies of low volume sealed roads in southern Africa by TRL since 1994 are described. A summary of the new materials specifications and design requirements for low volume sealed roads in Zimbabwe, a flow chart for the sealed road design process, and a pavement design chart for sealed widths less than 7m are presented. Considerable cost savings are possible using these specifications. The performance of a wide spectrum of test pavement sections was monitored and life cycle costs were compared for different design traffic levels. Differences in the rate of roughness progression were shown to be the most important means of discriminating between the performance of the test sections from a technical and economic viewpoint. The environmental component was the most influential contributor to the roughness of a road for low volume roads. Because of lower reseal frequency, double seals gave lower discounted overall costs than single seals. Controlling the moisture environment both within and in the immediate vicinity of the road is considered a dominant factor in future performance. The higher costs of providing and maintaining increased crown height and foundation standards minimised life cycle costs at higher traffic levels.