The Federal Highway Administration (FHA) sets the maximum gross vehicle weight (MGVW) at 80,000 pounds, while permits for overweight loads and specific bridge and highway corridor weight limits are under the purview of each state. States are also responsible for collecting and distributing funds for the repair and maintenance of roadways and bridges.
The U.S. DOT has identified a shortfall in infrastructure funding and thus anticipates the potential for a crisis in some states related to the deteriorating condition of many roadways and bridges. The gap between critical infrastructure maintenance priorities and the funding required to complete the recommended repairs is often higher in states that issue a larger number of heavy load or overweight freight permits, have extensive truck traffic, and also more extreme weather patterns. Identifying and implementing a dedicated source of sufficient funds for infrastructure repair is currently at the forefront of discussions in many state legislatures.
In the U.S., local, state, and federal government agencies along with the trucking industry are exploring numerous options intended to meet both the need for an increase in goods and materials transport volumes, and a sustainable highway system. This article looks at some of the causes and potential solutions for this dilemma from a variety of perspectives including:
- How overweight loads contribute in varying degrees to road damage via distributed axle weight verses gross vehicle weight,
- How inadequacies in the current tax system result in inadequate funding for the repair of roads and infrastructure,
- Available examples of Statewide research into the cause and effect of and possible mitigation measures for the damage to roadways due to trucks that frequently approach the maximum weight,
- How some states are utilizing fines, fees, and potential legislation (state and national) to curb weight limits, or minimize their impacts, and
- Trends in freight transport technology.
Despite the variety of roadway designs, materials, and construction techniques currently used to prevent or deter roadway degradation, heavier truck loads that approach or exceed the current 80,000 pound gross vehicle weight limit are a factor in accelerating the damage to roadways and bridges. According to the website Pavement, the damage caused by a single axel is exponential rather than linear.
The Pavement website provides an example of how the weight of 18,000 pounds on a single axle does over 3,000 times more damage to pavement than 2,000 pounds on a single axle. Their calculations make it clear that the damage and force goes up dramatically from there. Therefore, one option for minimizing impacts is to increase the number of axles and distribute the weight of the freight more evenly.
Still, with an increasing demand for goods and a shortage of qualified drivers, the pressure on drivers to haul more freight per load is increasing. The trucking industry is doing it’s best to meet system-wide demand while faced with the uncertainty of governmental entities and trade associations advocating for overweight freight reform.
For example, the Coalition for Transportation Productivity (CTP), advocates raising the minimum weight to 97,000 pounds, spread over six (6) axles.
The Coalition’s argument is that adding a sixth axle would result in less weight per axle, which would provide a “softer” footprint distributed across the truck, thereby reducing pavement damage. Despite its approach, which differs from other groups hoping to restrict weight limits, the Coalition and others are cognizant of taxation’s inability to finance road repairs by itself.
A recent research report produced by the Research Advisory Committee of the American Association of State Highway and Transportation Officials (AASHTO) detailed Indiana, South Dakota and South Carolina’s research into solving the aforementioned infrastructure dilemma. This research included an assessment of whether or not truck permit revenues were covering the cost of road damage that could be attributed to trucks operating at or near the maximum weight limits. It then looked at the research into the viability and accuracy of axle-based and flat rate fees as alternatives to current gross weight regulations. The research also explored tire configurations and pavement types.
The DirectoryDirectory of Significant Truck Size and Weight Research, which was submitted to the National Cooperative Highway Research Program’s highway oversight panel, explores the concept of spreading freight weight over more axles. Again considering the effects of commercial truck weights that exceed the 80,000-pound maximum on roadway damage and its costs, the research directory provides a state-by-state breakdown of case studies that look at the issue from a wide variety of data points.
In Michigan, where MDOT, AASHTO and others have collectively concluded via research that pavement damage is directly related to axle loads – not gross vehicle weight – the laws reflect this conclusion. This has resulted in Michigan’s truck-weight law being designed to control axle loads instead of gross vehicle weight limits. Michigan’s law is based on the philosophy taken from the 1979 Turner Proposal.
While states are individually conducting extensive research and often implementing greater fines and roadway specific restrictive covenants to mitigate the problem, Congress intends to provide some national guidance legislation. The latest is the “Safe Highways and Infrastructure Preservation Act of 2013,” which seeks to alter truck size and weight limits on the National Highway System. Currently, the bill has been referred to committee in both the House and the Senate.
Simultaneously, the Federal Highway Administration study on Freight Management, which was ordered in the MAP-21 bill, compares the effects of tractor-trailers of different sizes and weights on roadways. The study, which will be submitted to Congress this November, analyzes axle weight distribution as well as all other aspects that impact safety, infrastructure, enforcement and competition.
While containerized intermodal freight transportation has been less of an issue in this ongoing debate, the entire trucking industry from carriers to equipment manufacturers are doing their part to affect positive change where possible. This includes various aspects of vehicle design improvements, improved GPS tracking and routing as well as the design and engineering of suspension performance advancements that reduce pavement damage.
The solution to these infrastructure issues must be a joint effort from all sectors. It is unlikely that there will be a one size fits all solution, so flexibility should be incorporated. Since the issues of overweight freight restrictions and aging infrastructure are intertwined, an innovative approach that tackles the challenges from all perspectives is needed.
 The maximum allowable gross vehicle weight on the heaviest “Michigan-weight-law MDOT Intermodal truck” is 164,000 pounds, which can only be achieved by use of eleven properly-spaced axles. Most of these axles carry only 13,000 pounds each. The alternative to a single Michigan combination carrying 160,000 lbs. on 11 axles is two standard trucks carrying 160,000 lbs. on 10 axles. Policy Division Policy/trucking/Truck Weights Michigan_3_21_13.doc Page 2 PDF Link