Practices for Permitting Superheavy Load Movements on Highway Pavements (2015)

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PRACTICES FOR PERmITTIng SUPERHEAVY LOAD mOVEmEnTS On HIgHWAY PAVEmEnTS This Synthesis captures the state of the practice in permitting superheavy commercial vehi- cles (SHCVs) or “superloads.” These are trucks that exceed the thresholds set for overweight vehicles allowed to operate with annual permits throughout state highway networks. Instead, SHCVs are issued single-trip permits on specific routes, following some type of engineering analysis. Work for this synthesis consisted of a literature review and a survey questionnaire. The literature review covered the SHCV permitting regulations and fees for the United States and the Canadian provinces, as well as efforts undertaken in Europe, Australia, and South Africa to harmonize weight regulations between their member states. The survey question- naire was designed to collect additional detail on the practices that U.S. states and Canadian provinces implement to handle SHCV permits. The literature review revealed that the practice of permitting SHCVs in the United States varies widely between states in terms of both permissible vehicle configuration and weight and the amount of the permit fees levied. The gross vehicle weight (GVW) thresholds used to define SHCVs vary from 120 to 254.3 kips. Axle load limits by configuration also vary; ranging from 20 to 29 kips for single axles on dual tires, from 34 to 60 kips for tandem axles on eight tires, and from 50 to 81 kips for tridem axles on 12 tires. In addition, some states set limits on the tire weight per unit width (i.e., it varies between 500 and 800 lb/in.), whereas other states do not. This lack of uniformity in weight regulations effectively reduces the weights of SHCVs traveling through multiple jurisdictions to the least common set of rules in effect through the jurisdictions involved. There have been regional efforts to establish uniform heavy truck permitting regula- tions in the United States, whereby a permit issued by one state is accepted for travel in other states. Twelve western states, under the auspices of the Western Association of State Highway and Transportation Officials (WASHTO), Arizona, Colorado, Idaho, Loui- siana, Montana, New Mexico, Nevada, Oklahoma, Oregon, Texas, Utah, and Washington, agreed on a uniform set of truck weight regulations that allow trucks permitted in one of these states to legally operate throughout the rest. In summary, these limits consist of a GVW of 160 kips; tire weights of 600 lb/in. of width; overall consecutive axle weight limits governed by the Bridge Formula; and axle configuration weight limits of 21.5, 43, and 53 kips for single, tandem, and tridem axles, respectively. Similar regional efforts are being undertaken in other geographic regions of the country under the coordination of AASHTO’s Subcommittee on Highway Transport (SCOHT). Future efforts of this com- mittee will include harmonization of oversize requirements, coordination of the truck permitting processes with local governments, development of a guide for assessing pro- posals for changes in truck size and weight standards, and formation of a state–industry advisory group on the movement of “superloads.” It can be noted that other industrialized countries such as Canada, Europe, Australia, and South Africa already have such regula- tions in place. SUmmARY

2 The literature review suggests that SHCV single-trip fees vary widely between the 62 jurisdictions in North America (i.e., 50 states, the District of Columbia, ten Canadian provinces, and the Yukon Territory): • Twenty-three (37%) levy SHCV permit fees that are a function of weight-distance, typi- cally in the form of $/ton/mile for GVW exceeding a certain value. Interestingly, some of the states that use weight-distance taxes do not use the same approach for levying SHCV permit fees. This fee ranges from $0.006/ton/mi to $0.2/ton/mi, with an average value of about 0.049/ton/mi. • Fifteen (24%) levy SHCV permit fees that are related to GVW/axle weight alone and do not consider at all the distance traveled by the vehicles. • Eight (13%) levy a flat SHCV permit fee that ranges from $5 to $550 regardless of any pavement usage indicators; that is, the weight of the vehicle or the distance traveled. • Seven (11%) levy a processing fee and may add an infrastructure usage fee after study- ing SHCVs on a case-by-case basis. • Two jurisdictions (3%) levy a flat fee and the cost of repairing the infrastructure from any damage rather than the cost infrastructure utilization from SHCV movement. A web-based survey was conducted between January and July 2014 to collect more detailed information on the practices of U.S. states and Canadian provinces in permitting SHCVs. A total of 39 states and five Canadian provinces responded to the survey ques- tionnaire (i.e., response rates of 78% and 50%, respectively). Eight states submitted two responses, one by its permit officer and one by the engineer who analyzed the impact of SHCVs, bringing the total number of survey responses to 52. The definition of a SHCV or “superload” varies significantly among jurisdictions. Sixteen of the responding agencies (41%) define SHCV in terms of GVW alone, five (13%) use GVW and axle loads regardless of axle spacing, and another five (13%) use GVW and axle loads as a function of axle spacing. Interestingly, the remaining 13 responding agencies (33%) use an alternative definition involving vehicle size, tire loading, axle spacing, and roadway condition. The definition of what constitutes a non-divisible superload also varies signifi- cantly among agencies. Some define it in terms of one-half day of labor effort to subdivide, while others define it in terms of more than 3 days of labor effort to subdivide into smaller shipments. Thirty-eight agencies responded as to whether or not they conduct pavement analysis as part of their SHCV permit process. Of those, five (13%) always do (Delaware, Missouri, Louisiana, Tennessee, and Vermont), 15 (40%) do so depending on the circumstances (Arizona, Colorado, Iowa, Illinois, Indiana, North Carolina, North Dakota, Oregon, Wash- ington, Wisconsin, Wyoming, Texas, Virginia, British Columbia, and Ontario), whereas the remaining 18 agencies (47%) never perform such an analysis. The majority of the agencies that perform pavement analysis do so when dealing with a vehicle exceeding their definition of a SHCV. Details on the pavement analysis performed were provided by 15 states. Their majority uses either their own in-house developed mechanistic-empirical pavement analysis approach or the mechanistic methods developed by industry. Several agencies indicated that they use the 1993 AASHTO Guide for the Design of Pavement Structures and characterize the traffic in terms of equivalent single axle loads. None of the responding agencies uses the Mechanistic-Empirical Pavement Design Guide for analyzing the impact of SHCVs. Additional details on the pavement analysis performed by the 15 responding states sug- gest that the majority use representative thickness and layer/subgrade moduli and consider the entire length of the SHCV. About half of them consider only one wheel path, the actual number of tires in the wheel path, and the tire inflation pressure, while approximately 25% consider the vehicle speed. Furthermore, only four of the 15 responding agencies consider structural failure of the pavement layers and subgrade as part of the SHCV permitting analysis.

3 Only two of these four states gave details on the actual method used for analyzing the struc- tural stability of the pavement layers. One indicated using the Mohr–Coulomb method, whereas the other reported using a slope-stability approach for this purpose. The results of the survey questionnaire confirmed the findings of the literature review on the various methodologies agencies use for computing SHCV permit fees. Fifteen of the 46 responding agencies (33%) use a GVW-distance-traveled approach (Alabama, Florida, Illinois, Ohio, Missouri, Montana, North Dakota Tennessee, Utah, Vermont, Washington, West Virginia, Wyoming, British Columbia, and Ontario), two use a pavement damage-distance- traveled approach (Arizona and Oregon), another two use a number of axles-distance-traveled approach (Idaho and New Jersey), while 19 (41%) use a different methodology. The findings of this study suggest that the practice of permitting SHCVs could be sig- nificantly improved through further study of their impact on pavements and implementation of the results in establishing equitable permit fees that cover pavement utilization and/or damage.