Damage to Bridges
According to the USDOT, bridge costs would skyrocket if LCVs were allowed nationwide, adding $319 billion in bridge costs ($53 billion in capital and $266 billion in user delay costs). Bridges are designed with a safety margin of error to ensure against bridge failure. LCVs would overstress some bridges, especially older ones, increasing the number of bridges that must be replaced, strengthened, or posted.

Bridge damage is determined by examining axle weight and spacing. A truck whose axles are close together will cause more bridge damage than a truck whose axles are spaced farther apart. A useful analogy is to think of a person standing on an icy lake. The person is more likely to fall through the ice while standing because weight is concentrated on one spot; but laying down spreads the weight, making it less likely the ice will crack.

Source: Comprehensive Truck Size and Weight Study, USDOT

Pavement Damage
Nationwide operation of LCVs could cause an additional $1.4 billion per year in pavement damage. Although the USDOT Comprehensive Truck Size and Weight Study found that there could be modest pavement cost savings ($398 million, a 0.2% decrease in pavement costs) from allowing certain LCV operation scenarios, it underestimated the amount of freight that would be diverted from rail to truck and it greatly overestimated the amount of freight that would shift from Single-Trailer trucks to LCVs. When these faulty assumptions are corrected, it is clear that pavement costs would increase with expanded operation of LCVs.

Source: Analysis of FHWA computer model by Roger Mingo, RD Mingo & Associates

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Infrastructure Damage by Heavier Single-Trailer Trucks

Damage to Bridges
Heavier single-trailer trucks would cause more bridge damage. Bridges are designed with a safety margin of error to ensure against bridge failure. Bigger trucks erode that margin of error, increasing the number of bridges that must be replaced, strengthened, or posted. Adding axles does not fix this problem. In its NAFTA Scenario, the USDOT calculated additional bridge costs of $329 billion ($65 billion in capital and $264 billion in user delay costs). Six-axle, 97,000-pound singles would cause a significant portion of that damage.

Bridge damage is determined by examining axle weight and spacing. A truck whose axles are close together will cause more bridge damage than a truck whose axles are spaced farther apart. A useful analogy is to think of a person standing on an icy lake. The person is more likely to fall through the ice while standing because weight is concentrated on one spot; but laying down spreads the weight, making it less likely the ice will crack

Source: Comprehensive Truck Size and Weight Study, USDOT

Pavement Damage
Heavier Single-Trailer trucks would result in a significant amount of pavement damage. Pavement damage increases exponentially with the weight of a truck. For example, one 80,000-pound five-axle truck does the same road damage as 9,600 automobiles and five-axle trucks operate well above 80,000 pounds in a number of states. A 100,000-pound five-axle truck does as much damage as more than 27,000 automobiles.

Proponents of bigger trucks argue that adding axles to heavier singles would ameliorate pavement damage. That is not true, however, if those axles are “lift axles.” (link to FAQs) Adding axles to ameliorate pavement damage makes trucks harder to turn but lifting the extra axle(s) eliminates that difficulty. If the life axle is too high, however, the truck is overloaded. Studies of lift axle use as well as anecdotal evidence from truck enforcement officers show that lift axles are often improperly used, either purposefully or due to poor maintenance. There is also evidence that tridem axles (link to FAQ), which would be used on six-axle tractor-trailers, cause damage to pavement subsurfaces and slabs that most studies do not consider.

Sources: Pavement damage calculations are based on the American Association of State Highway and Transportation Officials (AASHTO); Louisiana DOT Study, 1999.