Overload road damage model

Abstract

Not only do overloaded vehicles pose an increased safety risk on the road (reduced stability and braking efficiency etc.), but they also accelerate the rate of deterioration of the road network and increase road maintenance costs, which in turn makes many of the roads less safe for travel by other road users (rutting, potholes etc.). Overloading also results in unfair competition between those operators that overload and those that operate within the legal limits. The annual damage to the network of provincial and national roads caused by overloading was estimated in 1995 to be R450 million per annum. At today’s prices, this figure would be between R700 and R800 million per annum. However, this figure is now considered to be far too low, as recent studies have shown that the South African heavy vehicle fleet has changed over the past few years and now consists of a higher proportion of high payload vehicles, than in the past. Also, the general condition of our roads has deteriorated to the extent that even slight overloads result in high values of pavement damage. To combat the overloading problem overload control strategies and programmes are implemented by various state roads and traffic law enforcement departments. This can be quite costly and such strategies and programmes need to be evaluated on a life-cycle cost basis. One of the benefits of increased overload control is a reduction in damage to the road network infrastructure with a subsequent saving in maintenance costs. A spreadsheet based model was develop to calculate this potential saving in maintenance costs and was then applied to two example, one the N1 Corridor in the Free State and the second the N2 and N3 in KwaZulu-Natal. In order to illustrate to transport operators the benefit to them of reducing overloading, an analysis was also done of the impact of the deterioration in the condition of the road network on vehicle operating costs.