AXLE LOAD LIMITS IN ONTARIO: LONG-TERM ANALYSIS

Overloaded axles contribute significantly to the deterioration of road structures. Protection against severe pavement deterioration is provided in most jurisdictions by limiting permissible axle loads for commercial traffic. Within most provincial jurisdictions in Canada, axle load limits have been set arbitrarily with little reference to economic viability. In practice, axle load limits have been established from past experience based essentially on two conditions: (a) the need to maintain a reasonable level of serviceability on the road network and (b) available monies for annual rehabilitation and maintenance programs. The financing of rehabilitation and maintenance programs is supported from general revenues for each jurisdiction, and this allocation of funds may have little relevance to the incidence of costs and benefits to users of the road system or to the responsible transportation agency. In this study two actual axle load distributions are investigated to assess the effects of changing the axle load limits on transportation costs. These costs include pavement rehabilitation and maintenance and commercial and noncommercial vehicle operating expenditures. In Ontario the vehicle operating costs for commercial traffic are the dominant cost component that influences the economic viability of axle load limits. The increased operating costs of noncommercial traffic from reduced pavement serviceability appear to mitigate against increases in the maximum allowable axle load. Furthermore, long-term changes in truck fleet composition, resulting in a more efficient distribution of axle loads, may produce conditions under which higher axle load limits are economically justified.