Beyond the abandoned factories and neighborhoods, a surprisingly striking feature of Detroit were the eleven axle trucks rumbling around Michigan’s highways. They caused me a lot of double-takes considering I’ve grown accustomed to no more than five axles on a standard Class 8 vehicle. The use of these multi-axle trucks stems from Michigan’s laws concerning maximum axle loads. Federal law states that no vehicle can surpass 80,000 lbs. in gross weight spread over five axles. This federal law, however, grandfathers in state laws allowing more axles and more weight. Thus, in Michigan, trucks with eleven axles are allowed to carry 164,000 lbs. According to MDOT, “Research conducted by the American Association of State Highway and Transportation Officials, the Michigan Department of Transportation (MDOT), and other organizations, has shown that pavement damage is directly related to axle loadings, not gross vehicle weight.”
These trucks might look strange to an unaccustomed Hoosier, but the studies seem to suggest they do no more damage to the road than your typical eighteen wheeler. On an eleven axle truck in Michigan, most axles carry only 13,000 lbs. each, whereas a typical class 8 truck complying with federal law carries 17,000 lbs. on each axle and 12,000 lbs. on the steering axle.
According to MDOT, while the number of trucks operating over 80,000 lbs. are relatively few, they provide great economic benefits to the state. Michigan’s economy relies heavily on manufacturing, mining, forestry, agricultural and construction sectors, all of which benefit from being allowed to carry more product per trip. Additionally, less trucks on the road means less congestion. The federal government obviously has not bought into these advantages, but at least for now, Michigan sees a great deal of benefit from allowing multi-axle trucks on its highways and roads.
Source: http://www.michigan.gov/documents/mdot/MDOT_013-4-16TruckWeightsMichigan_418609_7.pdf
This could be related to the article someone posted about the infrastructure in the US. States could start encouraging transportation firms to use more axles to make the deterioration of the pavement slower.
It is funny that in my country where they seem to love doing everything wrong they charge for the amount of axles at toll booths without measuring the weight per axle, making trucks use less axles than the ones permitted, affecting the pavement negatively.
As per Juan’s comment, you can also find tolls based on the number of axles in the US – you’d see that if you looked carefully at the ticket we got on the Ohio Turnpike.
While road wear and tear may be a function of the weight on an axle and not that of the truck, surely braking is worse? or maybe they are in fact no more dangerous….but didn’t you see not tandem but triple trailer-trucks in Michigan? That surely could let a trucking firm lower weight per axle, but I worry about swaying and jack-knifing in sudden stops. For new trucks and firms willing to pay, traction control does help a lot.