There’s a complicated formula that the federal government uses to determine the weight limits per axle within the commercial trucking industry. The weight limits are designed to place less stress on road surfaces, thereby facilitating more efficient transportation of products and goods. Weight limits were also enacted as a safety measure in the event that a truck has to swerve, change lanes or avoid obstacles.
Federal law dictates that single axles are limited to 20,000 lbs. and gross body weight is limited to 80,000 lbs. Truck axles that are spaced more than 40 inches, but not more than 96 inches apart (tandem axles), are limited to 34,000 lbs. However, states also have their own set of weight limits that can be significantly different than federal specifications.
The specifications are obviously different for heavy haulers and there are multiple levels. The first is for those hauling 120,000 to 140,000 lbs. The second level is 140,000 to 180,000 lbs., followed by 180,000 to 240,000 lbs. The fourth level is for loads of 240,000 to 330,000 lbs.
Power and Balance
In addition to selecting the optimal tractor-trailer combination, companies must also consider a myriad of other factors during a heavy haul job. They must balance the tractor against the weight to ensure the tractor has enough power to move the load while obtaining the best fuel mileage. Other elements include the distance to be driven and the type of terrain, such as steep grades or frequent starts and stops.
The axle distance and weight limits per axel were designed to protect roadways, bridges, and the public as trucks began carrying heavier loads in the 1950s and 1960s. The specifications linked the spacing and number of axels to overall weight. Without significant upgrades and updates to existing infrastructure, changing those specifications could result in serious damage to roads and bridges.
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