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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - March/April 2006

March/April 2006
Issue No:
Vol. 69 No. 5
Publication Number:
Table of Contents

Mileage-Based Road User Charges

by Mileage-Based Road User Charges

As vehicles evolve and burn less fuel, fees assessed for the number of miles actually traveled may prove to be a stable, efficient, and equitable way to finance roads in the United States.

Even electronic tolls, such as the FasTrakTM collection program in California's Bay area, shown here with traffic backed up at a toll plaza, are subject to congestion. A mileage-based user charge system could make tolls and long lines like this one a thing of the past. Photo: AAA Foundation for Traffic Safety.

For almost a century, the motor fuel tax has been the mainstay of highway finance in the United States. This method has the advantage of being roughly proportional to the distance traveled and thus has the desirable attribute of being a pay-as-you-go form of user charge. In several important dimensions, however, motor fuel taxes may not be entirely satisfactory.

In future years, the revenue-generating capacity of the motor fuel tax will be at best problematic. The U.S. Department of Energy predicts that fuel efficiency will improve substantially through 2025, with automobiles achieving nearly 13 kilometers per liter (30 miles per gallon) on average in that year. The California Air Resources Board and the National Research Council also predict substantial improvements in fuel efficiency for the vehicle fleet by 2015 to 2020. Absent substantial increases in fuel tax rates per gallon, receipts are not likely to keep pace with costs.

Further, to help the United States become more energy independent and to improve the air quality in major cities, the auto industry and the Federal Government are working together to design a new generation of vehicles that are either hybrid—a combination of electric and conventional internal combustion power—or are powered by hydrogen fuel cells. Several auto manufacturers also are experimenting with internal combustion engines powered by hydrogen. Various prototype fuel cell vehicles have performed favorably, and hybrid vehicles already have entered the marketplace.

According to industry and trend analysts, Plunkett Research, Ltd., "2004 through 2005 will long be remembered as a pivotal period in the automobile industry. It was a period during which high gasoline prices started a sea change among U.S. consumers that will finally create significant demand for fuel-efficient vehicles."

Although it may be a few years before vehicles with these new propulsion systems become prevalent enough to severely impair motor fuel tax revenues, the day almost certainly will come. In the short run, it may be possible to raise the motor fuel tax sufficiently to offset increases in fuel efficiency of the vehicle fleet, but in the longer term, projections show that the gap will grow between highway needs and highway funding. Therefore, new solutions to road financing will be needed.

According to James March, team leader in the Federal Highway Administration's (FHWA) Office of Transportation Policy Studies, "This is a propitious time to explore a new approach to assessing road user charges—one that will accommodate vehicles with any of the possible propulsion technologies and also facilitate implementation of a variety of public policies related to more equitable and efficient charges for highway use."

Minnesota Lieutenant Governor Carol Molnau, who also serves as the State transportation commissioner, says that while "the fuel tax has been a reasonable funding source over the years, it may grow less viable as we see extreme variations in vehicle efficiency. Although it may take years to implement a system to replace fuel taxes with a new kind of revenue source, it is our responsibility to take the long view."

Stuart Anderson, director of the systems planning office at the Iowa Department of Transportation, takes a similar view. "As more hybrid vehicles enter the fleet and additional work is underway on alternative fuel vehicles, it is important that new user fee methodologies are evaluated on a national basis," he says.

Indeed, transportation experts say that the broadest view will look beyond user fees to a range of potential revenue sources. "The mileage-based tax is just one of these that could possibly be viable in the future," says Molnau. "There is no simple solution, and there is no single solution."

State and local governments could consider several policy directions that would increase the role played by user charges, including the following:

  • Increase the motor fuel tax
  • Assess development impact fees
  • Implement tolls more aggressively
  • Develop an entirely new approach based on vehicle miles traveled

In future years, policymakers will need to evaluate options such as these for characteristics including: fair distribution of cost burdens, ability to provide a long-term stable source of revenue, and capacity to support other social and economic initiatives that local governments may wish to pursue.

Fuel cell cars, such as the ones lined up here, are still in the development stage, but if they enter the mainstream in significant numbers, they could help make gas taxes obsolete.

Motor Fuel Tax Increases

Until alternative propulsion systems become commonplace, and if the public-political will exists, one option to generate revenue to support the Nation's transportation systems is to increase Federal and State motor fuel tax rates. The motor fuel tax, however, has proven inequitable. In the 1997 Federal Highway Cost Allocation Study, FHWA concluded that heavy vehicles underpay for their road use because the damage they do to roads is much greater than the amount paid in fuel taxes, especially when compared to the damage caused by lighter vehicles.

Likewise, Road Work: A New Highway Pricing and Investment Policy by Kenneth A. Small, Clifford M. Winston, and Carol A. Evans indicates that for each mile traveled, an 11,793-kilogram (26,000-pound), single-unit, two-axle delivery truck may impose pavement costs 1,000 times higher than caused by an automobile. Although the truck is likely to burn about three times as much fuel per mile, and therefore pay three times as much fuel tax per mile traveled, a substantial cross subsidy from auto drivers to truck operators results.

Any number of variations of alternative fuel vehicles could come online in the years ahead, all crimping the usefulness of the traditional gas tax. Here, a technician works on the engine of a car that uses a combination of hydrogen fuel cells and electric batteries for its propulsion.

In a similar vein, an auto traveling in heavily congested traffic imposes delay and environmental costs that are far greater than a comparable vehicle traveling in free-flowing traffic. The former will burn more fuel, but the difference in fuel tax paid generally is far less than the difference in delay and environmental costs imposed. Because the fuel tax is unable to charge individual classes of vehicles or road users at a rate comparable to the costs imposed, various inequities among road users result. Another inequity, for example, is that the jurisdiction in which a vehicle travels and imposes costs may not be the same as where its fuel was purchased and the fuel tax paid.

In A New Approach to Assessing Road User Charges, a research team from the University of Iowa concluded that the motor fuel tax is a blunt instrument that is not sufficiently flexible to enable even a simplified form of road pricing. Given the equity problems it creates, this tax does not have a promising future from either a revenue generating or a pricing perspective.

Gasoline will continue to be the primary fuel for vehicles for some time, but the emergence of other fuel sources raises questions as to the viability of continuing to rely on the gas tax to fund highway projects.

Development Impact Fees

In recent decades, economists began to consider development impact fees as a means to finance a portion of the additional roadway capacity required to accommodate new development within a community. A common motivation for levying such fees is to reduce the burden on those who pay the local property tax. These one-time fees require that each new residential or commercial project pay its prorated share of the costs of new or widened arterial streets and roads that will serve the project. This approach has the advantage of placing part of the cost of transportation improvements on those who contributed to the need.

In one sense, development impact fees are equitable because those most likely to use the new facility pay a portion of its capital costs, while others do not. Some researchers, however, note that these fees can be inequitable because they usually do not vary with the value of homes in a development; they only vary with the number of units and therefore the probable amount of traffic to be generated. It is noteworthy that these fees can reduce the affordability of housing for people with limited incomes.

Development impact fees are not a direct user charge because the users of the road improvements do not pay directly on the basis of their actual amount of use. Once constructed, the operation and maintenance costs of the new facilities must be defrayed in the same way as other streets and roads. Because the additional road capacity imposes further operating costs, impact fees do not in themselves constitute a solution to the problem of how to finance the operation of local streets and roads.


Tolls have been a part of transportation finance since the colonial period. They have the major advantage of being paid only by actual users of a road. In the United States, toll roads in Kansas, Massachusetts, New Jersey, New York, Ohio, and Pennsylvania, to name a few, have been operating for a half of a century or more. Other States including California and Florida also have added toll roads more recently. In urban areas, a growing number of tolling applications are designed as road pricing mechanisms. High-occupancy toll (HOT) lanes, for example, were implemented in San Diego on I-15; in Orange County, CA, on S.R. 91; in Houston on the I-10/Katy Freeway and U.S. 290; and in Minneapolis on I-394. A 274-kilometer (170-mile) HOT lane network is planned for the Washington, DC, metropolitan area as well.

HOT lane pricing enables vehicles with several occupants to drive free or pay a lower toll when traveling in a designated lane. If drivers of vehicles that do not meet occupancy requirements (such as solo drivers or two-person carpools in HOV-3 lanes, or single-occupant vehicles in HOV-2 lanes) wish to travel in this lane to avoid congestion, they must pay a toll that varies with prevailing traffic conditions (in San Diego, toll rates can change as frequently as every 6 minutes). Those traveling in other lanes do not pay a toll, but they must contend with congestion during peak travel periods.

Public response to HOT lanes on the aforementioned facilities generally has been favorable. In San Diego, for example, a telephone survey of 800 motorists who used the I—15 HOT lanes revealed an approval rating of about 90 percent. Early concern was that the tolled lanes would benefit mainly travelers who have comparatively high incomes, becoming so-called "Lexus lanes." In many cases, however, travelers with limited resources have benefited from HOT lanes by carpooling. Although tolling has significant potential, three problems may hamper the prospect of increasing the role of toll revenues in financing urban streets.

First, particularly in urban areas, the potential exists for traffic to divert from freeways and expressways with tolls to city streets without them, especially when these streets are parallel or would constitute shortcuts. Traffic diverting to routes through residential neighborhoods can endanger residents and perhaps increase traffic and congestion.

Second, double payment—tolls levied in addition to the motor fuel tax paid by all highway users—can constitute an inequity unless the facility on which they are paid offers superior service, in which case the toll becomes a form of surcharge. Equity also may be violated if tolls collected on only part of a road system are regarded as a means for financing the entire system.

Third, tolling has limitations as a pricing mechanism. Because only a small portion of the urban road system can support tolling, it cannot be used to price individual segments across a road system to encourage heavy vehicles to use appropriate facilities, discourage commuters from traveling through residential areas, or encourage use of fuel-efficient vehicles.

Like gas taxes, toll plazas like this one could become obsolete if mileage-based user charges were to come into widespread use.

Mileage-Based User Charge

With the advancement of global positioning system (GPS) and geographic information system (GIS) technology, a new approach to directly charge users has become more feasible. Now it is possible to accurately assess road user charges on the basis of the number of miles actually traveled. On behalf of the FHWA-sponsored Transportation Pooled Fund Program, which comprises representatives of FHWA and 15 State departments of transportation (DOTs), a research team at the University of Iowa developed a prototype mileage-based road user charge. The mileage-based approach is equally workable with any type of vehicle propulsion system, whether gasoline, electric, or fuel cell. (For more information, visit

Functionally, mileage-based road user charges have attributes similar to electronic tolls, but assessing them on lower standard facilities such as city streets and lower volume rural roads is more feasible. Whereas electronic toll roads use "smart road" and "dumb vehicle" technology (roadside readers and passive identification labels on vehicle windshields), the opposite is true with mileage-based charging approaches. The process of determining user charges is independent of the roadway, with all the necessary equipment residing on board the vehicle. Therefore, it would be feasible to charge for travel on all roads within a jurisdiction without the need for any roadside devices, and tollbooths could be eliminated. Controlling agencies also could vary the charge by type of road or vehicle.

Installing the necessary equipment during production would not be costly. "Under a mass production scenario, the unit cost of installing the requisite onboard equipment could be quite low, under $50," says Professor Jon Kuhl of the University of Iowa, "given that in a few years most new vehicles are likely to feature GPS receivers and given that the other necessary equipment is fairly simple."

A mileage-based user charge system would rely on GPS technology, by which satellites, such as the one depicted here, would provide signals that onboard vehicle systems could use to measure travel, and fees would be assessed according to the roads traveled and the jurisdictions in which the roads are located.

As determined by research for the FHWA-State DOT consortium, a basic receiver on board the vehicle uses GPS signals to determine its position, and the computer reconciles this position with a GIS file. The GIS file contains polygons that define State, county, and municipal political boundaries and enable the onboard computer to determine the jurisdictions within which travel has occurred. The computer, which contains a file with the charge rates per mile for participating jurisdictions, computes and stores the user charges based on the miles traveled within each polygon. When a vehicle crosses into another jurisdiction, it enters a different polygon, and travel within that polygon is charged accordingly.

Protecting Privacy

Transportation officials need to consider three important issues and opportunities when considering implementing a mileage-based road user charge: (1) protection of the privacy of road users, (2) parallel operation of the motor fuel tax and the mileage-based road user charge as the vehicle fleet turns over, and (3) simultaneous pursuit of other policy initiatives.

If mileage-based road user charges have an Achilles' heel, it is the public's concern that the Government will track people's movements. That concern is not without merit: various services available from auto manufacturers involve transmission of cellular signals that enable the service provider to know the exact location of a participating vehicle at all times. If a similar type of technology were used, it indeed could be an affront to those who prefer that government agencies or their contractors not be able to determine their location and movements.

This large-scale map shows data polygons for several Midwestern States. The boundary of each State would be defined in the GIS database in the onboard computer. Each State thus constitutes data polygon, indicated by the dotted lines outlining the State borders. Travel within a State would be measured by the GPS receiver, and the appropriate per mile charge would be applied as this travel occurs. When a vehicle crosses into another State, travel in it would be treated in the same way. Thus, what would be stored in the computer is the dollar amount owed to each State. The arrows indicate trips, either within or between States.
Source Transportation Research Record.

Research completed for the consortium shows that for a mileage-based user charge to work well, it is not necessary for a vehicle's location to be transmitted on a real-time basis. Further, it is not even necessary to store information that constitutes a record of where the vehicle is or has been. The only data that need to be stored are the dollar amounts owed to each jurisdiction in which travel has occurred. While the only identifiable data value will be the total amount owed for all jurisdictions, through encryption, anonymous information will be uploaded that specifies the jurisdictions to which the revenue is to be distributed .Therefore, a mileage-based user charge could in fact guarantee privacy protection while ensuring that the user charges collected are directed to the jurisdictions in which travel has occurred. There are tradeoffs between the need for privacy and the need for taxpayers to be able to verify the accuracy of charges. In the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), there are provisions to perform field tests on this type of user charge.

This smaller scale map shows data polygons for a State, county, and municipality. The figure highlights the capacity to assess a mileage-based user charge at the State level and supplement it with local charges at the county or municipal level. Vehicles traveling within a locally defined polygon would pay the State per mile rate and that assessed by the metropolitan area, county, or municipality. To finance its streets and roads, a participating community would be able to rely on user charges paid by all travelers within it and depend much less on nonuser taxes, such as sales or property taxes.
Source Transportation Research Record.

Parallel Operation

As a practical matter, retrofitting existing vehicles with the onboard computer, GPS receiver, and associated equipment generally would not be feasible. It would be relatively expensive to the vehicle owner, and because the onboard equipment would not be fully integrated with the vehicle's electrical system, tampering with or disabling it would be difficult to prevent. The central issue thus becomes how best to proceed with two very different approaches operating side by side as the vehicle fleet turns over.

Using production forecasts and scrappage data, the research team at the University of Iowa Public Policy Center concluded that if, beginning with the model year 2005, all new autos and trucks sold were equipped with the onboard computer necessary to implement the mileage-based user charge, by 2015 almost two-thirds of the autos in operation would be so equipped. By 2025 almost 95 percent of autos would be capable of supporting the mileage-based user charge. The researchers estimated comparable but slightly lower percentages for trucks.

One of the most pressing issues related to phasing in a mileage-based user charge, as it applies to conventional gasoline- and diesel-powered vehicles, is how to handle the payment of the motor fuel tax. On the one hand, motorists may argue that it would be unfair for conventional vehicles to pay both the fuel tax and a per-mile user charge. On the other hand, care must be taken to prevent fraudulent nonpayment of the motor fuel tax by operators of conventional vehicles.

One way to address this issue is for vehicles with the onboard equipment supporting the new approach to have a simple in-vehicle system to monitor fuel intake during refueling. The onboard computer would take note of the number of gallons of fuel transferred and the jurisdiction in which the fuel was purchased. A small data file stored in the onboard computer could contain the applicable motor fuel tax rates for all jurisdictions. Through a simple computation, the onboard computer could store a credit for motor fuel taxes paid, which would be applied against the total per-mile user charges due to the jurisdictions.

Policy Initiatives

A mileage-based user charge system would need to be designed with sufficient flexibility to facilitate pursuing other public policy objectives as well. Road pricing, for example, is one method that road managers could consider for promoting more efficient traffic flow as well as greater equity among road users (that is, user charges that more accurately reflect the costs that specific classes of users impose). Mileage-based road user charges could facilitate the following forms of local road pricing:

Cost Recovery. As documented in the FHWA Federal Highway Cost Allocation Study, the cost imposed by heavy vehicles varies greatly with the type of road traveled. Charging a higher per-mile rate for lower standard roads helps recover the higher costs, and it can encourage the operators of heavy vehicles to use roads that are better able to accommodate them. The potential for savings in road repair and reconstruction is considerable.

Traffic Reduction. In some communities during rush hours, arterials become congested and impatient motorists may cut through residential areas to save time. Heavier, relatively fast traffic on residential streets can pose dangers to children and other residents. By charging a relatively high per-mile rate on residential streets, particularly during peak hours, road managers could discourage cut-through traffic.

Congestion Management. According to FHWA, the Texas Transportation Institute, and others, traffic congestion is a steadily increasing problem facing most large metropolitan areas. In addition to policies such as greater investment in public transportation and more sustainable land use patterns, road pricing is a way of encouraging higher vehicle occupancies and trip shifts away from peak periods. Experiences in such applications as I-15 in San Diego suggest that public acceptance of this type of pricing may be increasing. To the extent that this is the case, road managers could readily structure a mileage-based road user charge to support congestion pricing.

New Auto and Truck Sales in United States, 1980-2000

(Millions of Units)
(Millions of Units)
Light Trucks
(Millions of Units)
Medium-to-Heavy Trucks
(Millions of Units)
(Millions of Units)
1980 8.979 1.964 0.268 11.211
1990 9.300 3.984 0.278 13.562
1995 8.635 5.703 0.388 14.726
2000 9.005 8.405 0.462 17.872

Source: U.S. Census Bureau and Automotive News.


Estimated New Vehicle Sales and Scrappage in United States, 2005-2025

(Millions of Units)
New Auto Sales
(Millions of Units)
Autos Scrapped
(Millions of Units)
New Truck Sales
(Millions of Units)
Trucks Scrapped
(Millions of Units)
2005 8.5 8.0 9.0 6.2
2010 8.5 8.0 8.8 6.1
2015 9.0 8.5 9.1 6.2
2020 9.0 8.5 9.2 6.3
2025 9.0 8.5 9.2 6.3

Source: Public Works Management & Policy, October 2005.


Estimated Number of Autos and Trucks in Use in United States, 2005-2025

(Millions of Units)
New Auto Sales
(Millions of Units)
Autos Scrapped
(Millions of Units)
New Truck Sales
(Millions of Units)
Trucks Scrapped
(Millions of Units)
2005 130.2 6.5 85.6 10.2
2010   33.4 102.7 31.3
2015 131.2 62.7 123.1 58.8
2020   131.7 147.6 79.0
2025 132.2 94.4 177.0 91.4

Note that sport utility vehicles and minivans are classified as light trucks and therefore are included in the truck totals. Source: Public Works Management & Policy, October 2005.

Facilitating Privately Financed Commuter Routes. Privately financed facilities become much more feasible with a mileage-based road user charge. Revenue collected on private facilities could be directed to the firms operating them. Multiple points of entry and departure would pose no problem, and toll collection facilities would be unnecessary.

Encouraging Use of Environment-Friendly Vehicles. Transportation officials and local decisionmakers could encourage use of alternative fuel vehicles by charging a lower per-mile rate for environmentally friendly vehicles or those that are fuel efficient. Each vehicle could be assigned to one of several categories based on fuel efficiency and/or level of criterion emissions as defined by the U.S. Environmental Protection Agency. At its discretion, a State or metropolitan area could assign a different per-mile rate to each of the vehicle categories.

Mileage-based user charges would allow for tiered fees, such as a higher rate for large trucks like the one shown here, since they cause disproportionate wear and tear on roads, something not accurately accounted for in gas taxes.

Improving Transportation Planning. Travel demand models are among the most important tools for transportation planning because they help analysts understand where travelers begin and end their trips. According to Professor Edward Beimborn of the University of Wisconsin-Milwaukee, current models have many serious limitations, including the quality of travel data that are fed into them. For one thing, behavioral elements (such as trip-chaining, which involves making multiple stops on a single trip) need to be more accurately represented. A mileage-based approach to assessing road user charges has the potential to provide origin-to-destination and route data that are dramatically better than those currently used in travel demand modeling. A system that collects only the necessary billing information from all motorists but offers the option of tying into the travel data collection system in return for minor reductions in user fees would provide enough detailed data to greatly improve analyses while protecting privacy.

Traffic and congestion like this could be better managed through mileage-based user charges, proponents say.


A mileage-based road user charge would offer a means of generating a stable revenue stream that would be unaffected by the method of vehicle propulsion. Once implemented, the system would entail a low cost of collection for both agency and users, and it could provide road users with improved information on the costs they impose on the road system. A mileage charge also would allow flexibility in pursuing a variety of public policy objectives. This system could facilitate pursuing other initiatives such as congestion pricing, privately operated tollways, lane-specific user charges to encourage carpooling, pricing to encourage use of environment-friendly vehicles and to reflect road damage imposed by different classes of vehicles, improved travel demand analyses, and a shift of the financial burden for roads from property owners to road users.

The evolving energy sector offers potential ramifications far beyond the gas tax. Shown here is one car manufacturer's prototype for a system that would power both a home and a vehicle.

Although not without its challenges, this new form of road financing has the potential to be a powerful tool for road managers to consider when forming Federal, State, and local transportation policy.

Mileage-based user charges could be set up to encourage use of environment friendly vehicles, such as the vans shown here fueling up on cleaner burning natural gas.

David J. Forkenbrock is director of the Public Policy Center and professor of urban and regional planning and civil and environmental engineering at the University of Iowa. His research focuses on transportation finance and policy initiatives to advance social and economic objectives. For the past 7 years he has led a research team to develop and test a multijurisdictional mileage-based road user charge. He now is leading a team that is conducting a national evaluation of this form of user charge.

Paul F. Hanley is an assistant professor of urban and regional planning and civil and environmental engineering at the University of Iowa. He also holds an appointment as a research faculty member at the Public Policy Center. His research focuses on transportation infrastructure investments as a policy tool. He is a member of the national mileage-based road user charge evaluation study team.

For more information, see or contact David J. Forkenbrock at

This article is the fourth in a Public Roads series on innovative financing. One of FHWA's priorities is encouraging the use of innovative financing.


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