Commercial vehicles and loads are generally of a size and weight that allows them to freely travel on our nation's highways; however, some are too large or too heavy (or both) to operate on a highway without posing a safety risk or potentially damaging highway infrastructure. A vehicle and load is considered oversized when the vehicle and the cargo it carries exceed the legal dimensions of length or width, as defined by federal requirements or length, height, or width as defined by state requirements for the state in which the vehicle will be traveling (see fig. 1). A vehicle and load is considered overweight when the vehicle and the cargo it carries exceed the legal weight limit as defined by federal and state requirements. When vehicles and loads exceed federal or state size and weight limits, carriers are generally required to reduce the size of the load to within the limits, if possible. Specifically, carriers must divide oversize or overweight loads of bulk goods such as corn, gravel, or mail into smaller loads unless they have special exceptions.overweight loads, such as sections of wind turbine towers, may receive permits to travel on a highway, if they can be safely transported without damaging pavements or bridges as determined by state requirements (see fig. 2). FHWA has established some federal vehicle size and weight requirements, collects some information on state enforcement practices, and provides some technical assistance to states related to truck size and weight issues. Federal laws and FHWA regulations establish standards for vehicle width, weight, and length on some of the nation's highways. Width and weight standards are set at maximums. The width standards generally require states to allow vehicles to be up to, but not exceed, 8 feet 6 inches wide (see fig. 4). Similarly, the weight standards generally require states to allow vehicles to be up to, but not exceed, 80,000 pounds in total vehicle weight. States cannot set lower width or weight maximums when these federal standards apply. Vehicles exceeding these width and weight standards are considered overwide or overweight. The federal length standards differ from the above width and weight standards in that they do not establish a maximum overall length for a vehicle. The length standard is a minimum standard set to ensure interstate commerce is not impeded by a state's requirements. The regulation provides only that states may not require permits for vehicles with trailers that are less than a specific length, which depends on the type of vehicle. For example, states cannot require trucks with a single trailer to obtain a permit for a trailer that is less than 48 feet. However, states may allow longer vehicles or trailers to travel without requiring a permit. According to FHWA officials, federal length and width standards are set to enhance interstate commerce by ensuring carriers can travel from state to state without undue restrictions on vehicle size. Maximum width standards are set to minimize infrastructure damage and assure safe traffic operations, and maximum weight standards are primarily to protect highways and bridges from damage from excessive weight and to assure safe traffic operations. FHWA's federal vehicle width, length, and weight regulations apply to a small percentage of the nation's highways. There are approximately 4,093,000 total miles of public highways and roads in the United States, and federal size and weight standards apply to designated highways of national importance, as shown in figure 5. The National Network connects cities on highways capable of safely handling larger commercial vehicles for interstate commerce. FHWA's vehicle size (width and length) regulations apply to the entire 200,000 miles in the National Network, which includes the Interstate System, while the weight regulations apply to the 47,000-mile Interstate System, and not the larger National Network. Also, the National Highway System (NHS)--those highways important to the nation's economy, defense, and mobility--is supported with improvement projects funded by almost $22 billion in federal-aid highway funds in fiscal year 2014. The federal size and weight regulations do not apply to about 50,000 miles of the 223,000 miles of the NHS. Therefore, size and weight regulations are applied differently and not on all types of federal highways. The federal size regulations apply to less than 5 percent, and the federal weight regulations apply to a little over 1 percent, of the over 4 million miles of public highways and roads. States can set their own size and weight standards where a federal standard does not apply to a certain highway, which can be either more or less restrictive than the federal standards, depending on the type of standard. For example, while the State of Michigan follows the federal width standard (8 feet 6 inches) for vehicles on the highways covered by federal regulations or on special state-designated highways, on all other highways, a truck's width cannot exceed a more restrictive state standard of 8 feet 0 inches. Conversely, New York is less restrictive on trailer lengths and allows 53 feet 0 inch long trailers--five feet longer than the minimum length states must allow on highways covered by federal regulations. Further, federal standards have not been established for all aspects of vehicle size allowed on certain highways of national importance. Specifically, Congress has not set a vehicle height requirement, nor given FHWA the authority to do so, for any federal highway. FHWA officials said that the decision to not have a federal height standard goes back to a decision made in the 1950's when the Interstate System was being constructed and the height clearances already varied from state to state. All states have set a maximum height at, or above, the standard semi- trailer height of 13 feet- 6 inches. In addition, while there are weight standards for the almost 47,000 mile Interstate System, there are no federal weight standards for the approximately 176,000 miles of highways on the federally important NHS and 153,000 miles of the National Network that are not on the Interstate System, as mentioned earlier. As a result, states determine the maximum truck height, length, and weight allowed and when a permit is required for these highways. Given these limits in federal standards for vehicle size and weight, states have the flexibility to set their own standards; however, as shown in the following sections, this flexibility results in a variance from state to state. In addition to establishing size and weight standards, FHWA oversees some state activities related to oversize and overweight vehicles and loads. FHWA's Office of Freight Management and Operations in Washington, D.C., and staff in each of FHWA's 52 Division Offices are responsible for communicating with states on federal standards regarding vehicle size and weight. FHWA requires states to prepare and submit an annual Truck Size and Weight Certification (Certification) and State Enforcement Plan. FHWA Division Offices are to review these documents to verify that each state is enforcing vehicle size and weight laws, and that state laws do not conflict with federal laws. Further, based on these documents and review of the states' size and weight enforcement operations, the division offices are to prepare an evaluation report for each state. If states do not provide their annual certification, or the Secretary of Transportation (Secretary) determines that a state is not adequately enforcing all state laws on the Interstate System and other federal-aid routes, then the Secretary can withhold 7 percent of that state's federal-aid highway funding while the state is given an opportunity to come into conformity with federal regulations or appeal the Secretary's decision. If the state fails to certify, or the certification is rejected and the state's appeal process is exhausted, the Secretary is required by law to redirect the 7 percent of the state's federal funding previously withheld to other states. FHWA officials stated that they and state officials work together to correct problems with the certifications to avoid withholding funding from states and, as a result, have not withheld or redirected funding from any state since fiscal year 1992. Pub. L No. 112-141, SS 32801, 126 Stat. 405, 816 (2012). MAP-21 is the current authorization act for surface transportation programs and expired at the end of fiscal year 2014. Programs and budget authority authorized by MAP-21 were extended to May 31, 2015. Pub. L. No. 113-159, SS 1001(a),128 Stat. 1839, 1840 (2014). Among other things, section 32801 of MAP-21 required DOT to conduct a comprehensive truck size and weight limits study addressing differences in safety risks, infrastructure impacts, and the effect on levels of enforcement between trucks operating at or within federal truck size and weight limits and trucks legally operating in excess of federal limits. emergencies as set out in on MAP-21. Additionally, FHWA in cooperation with the trucking industry and the Commercial Vehicle Safety Alliance funded the development of pilot car escort and law enforcement escort best practices guides in 2004. FHWA officials told us that they are planning to provide staff support to update the pilot car escort best practices guide including providing research on stakeholder-identified priority areas, such as vehicle operations.funds administered by FHWA can be used by states in constructing some infrastructure, such as weigh stations, to enforce weight standards. FHWA's policy is to provide a safe and efficient highway network that can accommodate large vehicles, but FHWA plays a limited role in permitting oversize and overweight vehicles for several reasons. While FHWA's regulations establish standards for vehicle size and weight, according to FHWA officials, FHWA lacks the statutory authority to establish any requirements for state permitting. According to these officials, permitting practices are largely a state matter, and thus they do not keep records of states' permitting requirements or provide technical assistance on permitting to states. Officials from the 10 states we interviewed told us that the federal government provides them with little or no guidance on permitting. However, state transportation agencies--through their membership in AASHTO--have efforts under way to harmonize size and weight requirements and conditions under which they issue oversize and overweight vehicle permits. FHWA assists in an advisory role in this effort. FHWA officials told us that states are now working on changes to state administrative rules in order to harmonize requirements. States have varying laws and requirements that carriers must follow when operating vehicles on highways and bridges. Specifically, we found that states vary on vehicle size and weight laws, on state practices to issue and enforce permits for oversize and overweight vehicles, and on other state permitting requirements, as described below. All 50 states and the District of Columbia (D.C.) have state laws or regulations, based on applicable federal regulations, that set size and weight limits for vehicles operating in that state. Maximum vehicle width and weight requirements are generally set at the federal standard (8 feet 6 inches wide and 80,000 pounds for gross vehicle weight). However, states have varying size requirements for vehicle length and height. For example, 37 states set 53 feet 0 inches as the maximum legal length for a semitrailer, and length limits for the remaining 13 states and D.C. vary from 48 feet 0 inches to 65 feet 0 inches. Further, 29 states and D.C. set maximum vehicle height at 13 feet 6 inches, while the other 21 states allow vehicles to be from 14 feet 0 inches to 15 feet 0 inches. (Table 1 below summarizes vehicle size and weight requirements in the 50 states and D.C.) According to an AASHTO representative and state officials, such differences across states occur due to several factors, including age of infrastructure and changes to bridge clearance requirements over time. For example, Tennessee officials stated new bridges in Tennessee on the NHS are designed for a minimum vertical clearance of 16 feet 6 inches, while bridges on other routes have a minimum clearance of 14 feet 6 inches. Additionally, some standards were established in states a number of years ago and current state DOT staff may not know why they were established. For example, New York officials stated that a number of their requirements have been in place for decades and that officials do not know how they were determined, although carriers may have provided some input. States also administer differing processes to issue and enforce permits for vehicles that exceed their size and weight limits, and determine varying requirements that permitted vehicles must follow, as described below. Table 2 below summarizes these processes in the 50 states and D.C. Permit Issuing Agency: State governments issue most oversize and overweight permits; however, some local governments may also issue permits when carriers travel through local jurisdictions. State Departments of Transportation are often responsible for issuing permits. For example, states reported that state DOTs issue permits in 31 states and D.C. Permits can also be issued by state law enforcement, as in South Dakota, where South Dakota Highway Patrol Officers, trained in oversize and overweight enforcement, issue all state permits. In other states, the Department of Revenue or Department of Motor Vehicles may be the agency to issue permits. The number of permits issued annually varies greatly among states. For example, Texas issued the highest number of oversize permits in fiscal year 2013, around 400,000, while D.C. issued the fewest oversize permits, around 2,000. Trends in the number of permits issued vary from state to state, according to state officials we interviewed. Officials from one state described large increases in the number of permits issued, citing wind towers and oil industry activities as contributing factors, while another state described fluctuation in the number of permits issued, but no general increase. Oversize and Overweight Permit Types: States reported offering differing permit types that can allow oversize or overweight vehicles to operate within a state or between states. For example, Maine has 2 types of permits, whereas Pennsylvania offers 96. Some states differentiate between vehicle sizes to determine permit type and fees, while others create specialty permits based on industry. For example, Washington has a special permit type for vehicles transporting empty apple containers, and Texas has a special permit type for water well drilling machinery and equipment. States may also allow carriers to apply for a regional permit that allows carriers to apply one time and obtain permits for a trip on designated highways across multiple states. However, the size and weight requirements for a regional permit differ between regions, and 22 states reported that they do not participate in any regional agreement. Permit System: Permits may be issued by online- or manual- permitting systems, and the type of review can differ for each system. For example, online systems allow carriers to apply online, and some may issue permits without review from a permitting official for certain oversize or overweight vehicles traveling on established routes. For manual systems, state officials process permit requests, which can require face-to-face or phone contact. Overall, 44 states and D.C. reported offering online applications for permits, yet not all of these states automatically issue permits, and many such issued permits are for specific sizes and weights or specific routes. In some cases, states may need to work with carriers to find alternative routes in cases when permit applications are denied. State officials and others have varying opinions on the advantages of online permitting systems. For example, Tennessee officials said that some form of manual permitting was the safest option, while South Dakota officials said that online systems improved safety by removing human clerical error. Texas officials said that either way, they could not manually review all permit applications, because there are too many requests. Further, in its Accident Report on the Collapse of the Interstate 5 Skagit River Bridge, NTSB noted that a permitting process that enables a carrier to self-issue a permit online, without engaging the state in a technical review, does not motivate carriers to conduct surveys of the route to be traveled before transporting oversize loads even if a survey is required. Automated Routing System: Automated routing systems use clearance databases updated by state officials to provide a route to carriers. Twenty-three states reported they currently have automated vehicle routing capabilities. Officials in 8 out of the 10 states interviewed told us that automated routing systems could improve safety by removing human error or increasing compliance; however, 4 of the 10 states we interviewed currently offer automated routing. For example, South Dakota officials stated that their automated routing system was a benefit because it reduces the error rate while improving efficiency, safety, and carrier compliance. Additionally, Maine officials told us that while they do not have the capability, automated routing could make permit processing faster and more error-free. Not all of the states we interviewed agreed that automated routing would improve safety. For example, while Washington State officials are considering the development of automated routing, they do not see automated routing as a tool to increase safety. Additionally, Pennsylvania officials stated a primary benefit of automated routing systems would be ease of use for carriers. Permit Enforcement: States enforce compliance with permitting rules and regulations differently. For example, state officials we interviewed said they use roadside enforcement, administrative enforcement, or both to issue civil penalties or fines. Roadside enforcement generally involves law enforcement officers stopping an oversize or overweight vehicle and load to check for permits and compliance with state and local requirements. States may focus enforcement operations at fixed locations, such as at major border crossings or operate with mobile enforcement units, or both. According to state officials interviewed, the technology used in roadside enforcement can vary from yardsticks to sophisticated laser-measuring tools. For example, Texas officials told us that they use laser measuring systems with weigh-in-motion detection while Nebraska state officials said they physically measure vehicles with tape measures and traditional weight scales. Administrative enforcement can involve a review of permit documentation, a review of citations, or a review of carrier records collected by the state. State officials may review their records to identify carriers with numerous safety or permit violations. For example, Wisconsin permit officials told us they could enforce restrictions on repeat violators, shutting down their operation in the state by refusing to issue permits or by suspending licenses. Escort vehicles: Escort vehicles travel with an oversize or overweight vehicle and load to help protect the traveling public and infrastructure. The use of escort vehicles is widespread among states, though at different height and width thresholds. For example, 43 states and D.C. reported that they require escort vehicles for overheight vehicles and loads, although what is considered an overheight vehicle and load varies among states. All 50 states and D.C. reported that they require escort vehicles for overwidth vehicles and loads, although the threshold varies. Officials in 7 out of 10 states interviewed told us that requiring escort vehicles improves safety. For example, officials from Washington State and South Dakota said that escort vehicles improve safety because they improve visibility of the oversize or overweight load for other drivers. In 2004, SC&RA issued a best practices guide for escort vehicles, with participation from FHWA, although there is not a legal requirement that supports such a guide, according to FHWA officials. Escort vehicle driver certification: While the use of escort vehicles is widespread, many states currently do not require escort vehicle drivers to be certified. FHWA officials told us that there is no research that shows escort vehicle driver certification is a benefit to safety. Conversely, NTSB has previously concluded that the lack of standardization in certification of escort vehicle drivers leaves some drivers poorly prepared to carry out their duties and has recommended standardized training and certification for drivers. Thirteen states currently require such certification, which may involve training or passing a test. Of the 10 states we reviewed, two have such a requirement. For example, Washington State officials said that certification is a good practice that is required in their state, but cautioned that even with training and certification there is still the possibility of human error. Officials from 5 states of the 10 interviewed told us they have considered or are seeking to implement this requirement to improve safety or ease the burden of law enforcement officials, who may be required to escort. For example, Wisconsin officials said they would like to implement a certification process so that escort vehicle drivers can direct traffic. The remaining three states are not pursuing certification. For example, South Dakota officials said that they do not require escort vehicle drivers to be certified, because the lack of driver certification has not been identified as a problem. States have established processes and determined requirements for permitting of oversize and overweight vehicles over time. In some areas, states follow similar practices and requirements: for example, most states make use of online permitting systems and escort vehicles. However, other processes and requirements differ and state officials we interviewed did not always agree on the benefits of various practices, such as automated routing systems and escort vehicle driver certification. Nearly all state officials whom we spoke with told us that federal regulations standardizing permitting were unnecessary; however, some state officials we interviewed told us that more information on different permitting practices and their resulting benefits would be helpful to them to determine ways their state practices could be improved. For example, Texas officials stated that Texas's current permitting rules are sufficient, but they are always looking for ways to do things better. Maine officials told us that FHWA could help identify best practices in permitting, as states typically have constrained resources and do not have the capacity to conduct this type of research. We have identified key steps agencies can take to improve agency performance; one of them includes identifying best practices to help identify changes that might be needed to improve performance. However, according to all the state officials we interviewed, the federal government did not provide any or very little guidance used in oversize and overweight permitting. FHWA officials told us that although they collect limited information on state permitting practices, they do not have research or data that compare state permitting information or identify best practices due to lack of authority over state permitting. However, FHWA has authority to conduct transportation research, including research on issues with national implications that could lead to improvements in highway safety, and in the past has worked with the trucking industry and others to identify best practices for related issues such as escort vehicles. Our review uncovered examples of how research of state permitting to identify best practices could better position FHWA to provide technical assistance to states that could help inform state policy and legislative changes needed to improve their permitting of oversize and overweight vehicles. For example, some state officials we interviewed described the large upfront investment of money and resources to acquire an automated routing system as a limiting factor to their state having such a system. Officials in South Dakota, which currently uses an automated routing system, agreed that while their system was expensive to implement and difficult to obtain support for, the investment has led to benefits of improved efficiency, that the state has benefitted more than the cost of the system, and that its use can be considered a best practice. Also as previously mentioned, state officials we interviewed described the varying state requirements on certification of escort vehicle drivers. Some state officials we interviewed described how state decisions on certification of escort vehicle drivers could increase costs to carriers, as they have to cover the cost of certification, as well as affect the availability of state law enforcement officers to perform other commercial vehicle enforcement functions. By conducting this type of research, FHWA would be better positioned to help states make sound decisions to improve safety and protect infrastructure in a cost-effective manner. FHWA's policy is to provide a safe and efficient highway system that accommodates large vehicles, in part by regulating some aspects of vehicle size and weight and ensuring state enforcement of federal standards. However, FHWA has an opportunity to do more. Our review shows that state practices in regulating and enforcing oversize and overweight loads--in particular permitting practices--vary; further, states lack information on how well the range of practices being used actually work. In fact, FHWA has previously recognized the benefit in developing and distributing best practices in this area, as shown through its prior work with the trucking industry on an escort vehicle best practices guide. A similar study related to state permitting practices and requirements could help identify best practices to assist states in making decisions on their permitting practices. However, because FHWA does not collect information on state permitting, it is not in the best position to advise states on practices and requirements that could improve their performance. To improve stewardship over the nation's highways and bridges, we recommend that the Secretary of Transportation direct the FHWA Administrator to take the following action: Conduct a study on state oversize- and overweight-permitting practices, including automated vehicle routing and escort driver certification, to identify areas of best practice and share the results with states. We provided a draft of this report and the e-supplement to DOT for review and comment. DOT concurred with our recommendation and provided written comments, which are reprinted in appendix II. DOT also provided technical comments, which we incorporated as appropriate. DOT did not have any comments on the e-supplement. We are sending copies of this report to the appropriate congressional committees and the Secretary of Transportation. In addition, the report is available at no charge on the GAO website at http://www.gao.gov. If you or your staff have any questions about this report please contact me at (202) 512-2834 or flemings@gao.gov. Contact points for our Offices of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made key contributions to this report are listed in appendix III. This report examines (1) how DOT regulates and provides oversight of oversize vehicles and loads on highways and bridges and (2) how state agencies regulate oversize vehicles and loads on highways and bridges. For the purposes of our review, we defined an oversize vehicle and load to include when the vehicle and the cargo it is carrying exceeds the legal dimensions of length, height, or width as defined by federal and state requirements for the state in which the vehicle will be traveling. We defined an overweight vehicle and load as any vehicle or vehicle and load in which the vehicle and the cargo it is carrying exceed the legal dimensions for weight as defined by federal and state requirements for the state in which the vehicle will be traveling. The federal and state requirements that set size and weight standards could be in legislation or regulations. FHWA is the federal agency that oversees transportation of oversize and overweight vehicles and loads on highways and bridges. To determine how DOT regulates and provides oversight of oversize vehicles and loads on highways and bridges, we reviewed relevant legislation, obtained program documents from and conducted interviews with FHWA and FMCSA officials to obtain information on current policies, procedures, and practices for monitoring the transportation of oversize and overweight vehicles and loads. Specifically, we obtained information about what data FMCSA currently collects on oversize and overweight loads; how FHWA coordinates with state agencies; actions FHWA has taken in its oversight process; and challenges, if any, that FHWA faces in improving highway safety, infrastructure preservation, and interstate commerce in relation to oversize and overweight loads. In addition, we conducted a literature search to identify and review relevant studies, reports, and available data on oversize loads to gain a better understanding of the issue. To determine how state agencies regulate oversize vehicles and loads on highways and bridges, we conducted a literature review of and legal research on state laws, requirements, and restrictions on oversize and overweight loads. In addition, we conducted an online search of federal and state information about oversize and overweight vehicles and loads to identify data topics to collect and compare between the states. We reviewed commercially available information on states' vehicle size requirements, and then developed and administered a data-collection instrument to officials from the 50 states and the District of Columbia in order to verify various state permitting practices. We created an e- supplement GAO-15-235SP from this data that allows the user to compare different combinations of selected states. The data were verified by state officials in permitting and law enforcement. We developed the data collection instrument to send requests via email to state officials for verification of the data and additional information, including any data points unavailable online. We received completed responses from the 51 respondents for a response rate of 100 percent. We reviewed responses for inaccuracies or omissions, analyzed the data, and have presented the key findings in this report and the full findings in the e-supplement, which can be viewed at GAO-15-235SP. We also conducted interviews with state officials in 10 states to collect non-generalizable information on state permitting and enforcement practices related to oversize and overweight loads. We selected states that were (1) geographically diverse, (2) varied in the involvement of different regional permitting consortiums, (3) varied in the types of permitting requirements, (4) varied in the use of online electronic permitting, and (5) varied in crash and enforcement data availability. Using these criteria, we interviewed state officials from Iowa, Maine, Nebraska, New York, Pennsylvania, South Dakota, Tennessee, Texas, Washington, and Wisconsin. We used GAO's prior work on improving agency performance as criteria to identify key steps agencies could take to improve state practices. In addition, we also conducted interviews with representatives from national transportation organizations to obtain additional information on issues related to permitting and efforts by states to deal with these issues. Interviewees included the American Association of State Highway and Transportation Officials, the Commercial Vehicle Safety Alliance, the Specialized Carrier and Rigging Association, the American Trucking Association, and the National Pilot Car Safety Institute. Additionally, to understand the circumstances of the Interstate 5 bridge collapse in Washington State, we reviewed the National Transportation Safety Board (NTSB) documents, attended an NTSB Board meeting on the Interstate 5 bridge collapse, and interviewed relevant NTSB officials and investigators. We conducted this performance audit from April 2014 to February 2015 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives. In addition to the individual named above, Heather MacLeod (Assistant Director), Natalie Block, Brian Chung, Dave Hooper, Les Locke, Josh Ormond, Amy Rosewarne, Kelly Rubin, and Lorelei St. James made key contributions to this report. Also, Alice Feldesman and John Mingus made key contributions to the accompanying e-supplement (GAO-15-235SP).

Summary:
In May 2013, a truck carrying an oversize load crashed into an interstate bridge in Washington state causing it to collapse. This crash raised issues about oversize vehicles and public safety. DOT develops regulations on vehicle size and weight, and states enforce these standards with some oversight from DOT. States also issue their own regulations on vehicle size and weight and issue permits for oversize and overweight vehicles. The Joint Explanatory Statement of the Consolidated Appropriations Act for Fiscal Year 2014 required GAO to review the role of federal and state agencies in overseeing oversize vehicles. This report discusses (1) how DOT regulates and provides oversight of oversize vehicles and (2) how states regulate oversize vehicles. GAO collected information from 50 states and the District of Columbia about their permitting practices; reviewed relevant federal legislation and DOT regulations and documents; and interviewed DOT and state officials from a non-generalizable sample of 10 states, chosen based on a variety of considerations, including geographic diversity and types of permitting requirements. The Department of Transportation's (DOT) Federal Highway Administration (FHWA) has established some federal vehicle size and weight requirements and oversees some state activities. Based on current legislation, FHWA has established rules and regulations for vehicle width, truck trailer length, and vehicle weight standards for certain federal-aid highways aimed at protecting highways and bridges from damage while providing a safe and efficient highway network. FHWA does not, however, have the authority to establish a height requirement, a decision that goes back to the Interstate System's construction in the 1950's, when height clearances already varied from state to state. FHWA also oversees states' processes for enforcing these standards by reviewing states' documentation of enforcement operations. However, FHWA has more limited involvement in individual states' permitting processes and requirements, which the agency considers largely a state matter. For example, it does not provide technical assistance on permitting to states. State laws and regulations set varying size and weight limits and permitting requirements for vehicles that exceed these limits and that operate on highways and bridges. Specifically, GAO found that the vehicle size and weight limits set by state laws and regulations vary by state, although they are within the parameters of federal requirements. For example, states' length standards vary between the minimum federal standard of 48 feet and 65 feet for a semitrailer. GAO also found that permitting practices for oversize vehicles often vary by state. In some cases, states follow similar practices; for example, most states make use of online permitting systems and escort vehicles that travel with an oversize or overweight vehicle. However, other permitting practices vary by state--such as states' use of automated routing systems to provide a route for oversize vehicles. A National Transportation Safety Board investigation reported that differences among states on the various aspects of truck permitting could be a safety concern. State officials GAO interviewed did not always agree on the benefits of the various permitting practices, and some spoke of the need for more information on this topic. While FHWA is (1) conducting some research on the potential effect of changes to truck size and weight limits and (2) working with the trucking industry to update a best practices guide on escort vehicle operations, it has not studied permitting best practices across states due to lack of authority over state permitting. In GAO's prior work on improving agency performance, GAO found that identifying best practices can help identify changes that might be needed to improve performance. By conducting this type of research, FHWA would be better positioned to help states make sound decisions to improve safety and protect infrastructure. GAO recommends that DOT conduct a study on states' oversize- and overweight-permitting practices, including automated vehicle routing and escort driver certification, to identify areas of best practice and share the results with states. DOT agreed with GAO's recommendation and provided clarifying comments, which GAO incorporated.