Bigger can be better

The debate over whether larger combination vehicles (LCVs) harm or improve pavement life is a moot point in Michigan. Not only does the state allow vehicles with 11 axles to have a GVWR of 164,000 lb., it firmly believes such LCV configurations are better for the roads. Research by the Michigan Department of Transportation (MDOT) found that pavement damage is directly related to axle load, not gross

The debate over whether larger combination vehicles (LCVs) harm or improve pavement life is a moot point in Michigan. Not only does the state allow vehicles with 11 axles to have a GVWR of 164,000 lb., it firmly believes such LCV configurations are better for the roads.

Research by the Michigan Department of Transportation (MDOT) found that pavement damage is directly related to axle load, not gross vehicle weight. Consequently, Michigan law requires additional axles as GVWR increases. According to an MDOT white paper on size and weight, “Most trucks in Michigan carry between 13,000 and 16,000 lb./axle, compared to the average of 17,000 to 20,000 lb./axle in other states. This provision more evenly distributes the vehicle's weight among a greater number of axles, leading to less damage on our roads.”

Steven Karamihas, senior research associate with the University of Michigan Transportation Research Institute (UMTRI), concurs. “The name of the game is individual axle weight,” he states. “If you have bigger and heavier trucks, yet less axle weight and by extension fewer trucks overall, then you are going to get better pavement life without having to get into a different regime of pavement materials.”

There are some caveats, however, warns Karamihas. First, axle weight laws must be aggressively enforced. If LCV axles are overloaded, pavement life will be seriously reduced. Second, the impact of higher vehicle weights on some bridges must be accounted for, as well as the impact on maneuverability, performance and handling, etc.

“Bigger trucks are OK purely in terms of their impact on pavement life as long as you keep the per-axle weight low,” Karamihas adds.

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