section 2.0 Policy Implications; 2.1 Axle Weight Limits

Increasing axle weight limits will generally result in higher pavement costs, since pavement costs increase sharply with axle weight. However, past studies of truck size and weight limits have generally found that the increase in pavement costs would be much less than the decrease in goods movement costs associated with higher axle weights.

Conversely, reducing axle weight limits (or eliminating grandfather exemptions to federal axle weight limits) would result in lower pavement costs; however, the savings would be much less than the increase in goods movement costs. The Truck Weight Study found that the elimination of all grandfather exemptions would reduce pavement costs by $210 million per year. However, the cost of goods movement would be increased by $7,760 million per year if all grandfather exemptions were eliminated.

Several states have special limits on steering axles. The primary reason for these restrictions was concerns about loss of control due to the blow-out of an overloaded steering axle tire; however, the restrictions do provide some pavement cost savings. When viewed just in terms of AASHTO's load-equivalence factors, the savings are very small. However, the actual saving will be greater since steering axles usually have single rather than dual tires, and so the AASHTO factors understate their pavement wear impacts. Gillespie et. al. noted the pavement damage caused by a heavily loaded conventional tire on steering axles. For example, single tires on a steering axle carrying 12,000 pounds can be more damaging in fatigue and rutting to flexible pavement than a 20,000-pound axle with dual tires. They indicate that steering axle weights would have to be reduced to about 11,000 pounds to have the same pavement wear impacts as a 20,000-pound axle with dual tires.

[continued on next page, Page 10, Section 2.2 Bridge Formula ]

« Previous Page | Page 2.. Phase 1.1, Background. | 1.2 Truck Characteristics Affecting Pavements. (a) Axle Weights | Page 4, Section 1.2 [b] Tire Characteristics | Page 5, Section 1.2 (c) Suspension Systems | Page 6, Section 1.2; (d) Axle Spacing | Page 7, Section 1.2; (e) Liftable Axles | Page 8, Section 1.2; (f) Tridem Axles | Page 9, Section 2.1 Axle Weight Limits | Page 10, Section 2.2 Bridge Formula | Page 11, Section 2.3 - 80,000 Pound GVW Cap | Page 11, Section 2.4 Policies to Encourage Tridems | Page 11, section 2.5 Weight Limits Per Unit of Tire Width | Page 12, section 2.6 Turner Trucks | Page 13, section 2.7-New Approach; TRB Truck Weight Study | Page 14, section Section 3.0; Knowledge Gaps and Research Needs | Page 15, section 4.0 References for Pavements Working Paper | Next Page »

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