The Evolution of Heavy Truck Weights and Dimensions in Canada

Shifting Truck Size and Weight Regulations in Canada: A Historical Perspective

In the 1960s, Canadian and American truck size and weight regulations were similar. Most provinces used the same bridge formula as the U.S. for axle spacing and allowable weight. Weight limits for a five-axle tractor-semitrailer were prescriptive and capped at 73,280 lb. (33,566 kg), with axle weights for tandem groups capped at 32,000 lb. (14,515 kg) and 42,000 lb. (19,051 kg) for tridem axles. Overall length was restricted to 65 feet (19.81 m) with a 45-foot (13.72 m) semi-trailer. In the same period, A-train doubles were also in limited use in many parts of Canada.

Adapting Ontario's Truck Weight Regulations: Balancing Productivity and Safety Factors

In Ontario, the trucking industry persuaded the Department of Transport to allow weight increases in 1960 and again in 1966 to improve productivity. A survey conducted by the Department of Transport in 1967 revealed many overloaded axles on vehicles that were close to their allowable gross weight. This situation had gone unnoticed because the province used long platform scales to weigh trucks rather than axle scales, making the axle overloads not immediately obvious. The survey also revealed large numbers of short but heavily loaded trucks operating in the province, and there was a fear that these vehicle configurations might harm bridges because of the high weight concentrations over small areas. However, further studies showed that these particular "overloaded" conditions didn't appear to over-stress roads or bridges.

Evolution of Weight Regulations in Ontario: Introducing the Ontario Bridge Formula (OBF)

This revelation led to establishing the Ontario Bridge Formula (OBF) in 1970 as a safe operational load limit for bridges. The OBF introduced the concept of greater allowable weight on an axle group with a greater spread, and it became the means to control axle weights in Ontario, especially when it came to the short heavy vehicles mentioned above. The OBF allowed an increase in axle loads of about 10% over the previous rules. Tandem-axle weight limits increased to 35,000 – 39,000 lb. (15,875 – 17,690 kg) with axle spreads of 48 to 72 inches (1.22 to 1.83 meters). Tridem axles loads were increased to 44,000 – 60,000 lb. (19,958 – 27,215 kg) with spreads of 48 to 192 inches (2.44 to 4.88 meters).

Unintended Consequences: The Impact of the Ontario Bridge Formula on Truck Design and Roadway Infrastructure

However, although innovative at the time, the Ontario Bridge Formula became the greatest single influence on truck design in Canadian history, somewhat inadvertently. The formula did not impose any controls on axle arrangement or vehicle configuration. This lack of regulation allowed Ontario vehicle designers to create various vehicle configurations that could haul the maximum allowable gross weight of 140,000 lb. (63,503 kg). These included trailers with as many as six axles in multiple configurations. The rise of lift axles, which were difficult to control, led to unforeseen consequences such as drivers leaving the axles in a raised position while driving, resulting in grossly overloaded axles, suspensions, and tires — and significant damage to pavement and roadway infrastructure.

Reevaluating the Ontario Bridge Formula: Unveiling the Intentional Innovation or Oversight Debate

Despite being viewed as innovative then, the Ontario Bridge Formula needed to be better. There is some debate among engineers and researchers as to whether the lack of control over axle arrangement or vehicle configuration was an oversight or left open intentionally to spur innovation.


In conclusion, the evolution of truck weights and dimensions in Canada, particularly in Ontario, has been shaped by a series of regulatory changes and their subsequent impacts. The introduction of the Ontario Bridge Formula (OBF) in 1970 aimed to address concerns regarding overloaded axles and potential bridge damage. While the OBF provided a framework for controlling axle weights, it inadvertently allowed for a wide range of vehicle configurations to maximize gross weight limits, leading to unforeseen consequences.

Debate surrounds the intent behind the lack of control over axle arrangement and vehicle configuration in the OBF. Some argue that it was an oversight, while others believe it was intentionally left open to foster innovation within the industry. The resulting proliferation of complex vehicle designs, including trailers with multiple axles and lift axle systems, posed challenges in terms of safety and road infrastructure damage.

These insights highlight the need for continuous evaluation and improvement in truck weight and dimension regulations. Balancing innovation and safety considerations is essential to ensure the efficient operation of the trucking industry while minimizing negative impacts on roads, bridges, and overall transportation infrastructure. By learning from past experiences and engaging in ongoing research, policymakers and engineers can work together to refine regulations and support sustainable and safe trucking practices in Canada.


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