GAO-07-246R Underinflated Tires 

United States Government Accountability Office

Washington, DC 20548 

February 9, 2007 

The Honorable Byron L. Dorgan

United States Senate 

Subject: Underinflated Tires in the United States 

Dear Senator Dorgan: 

More than a quarter of automobiles and about a third of light trucks (including sport 

utility vehicles, vans, and pickup trucks) on the roadways of the United States have 

one or more tires underinflated 8 pounds per square inch (psi) or more below the 

level recommended by the vehicle manufacturer, according to a report by the 

Department of Transportation’s (DOT) National Highway Traffic Safety 

Administration (NHTSA).1

 A decrease in tire pressure can be caused by poor 

maintenance, driving habits, punctures, road conditions, and the quality of material 

used in tire construction. According to tire experts, under normal driving conditions, 

air-filled tires can lose from 1 to 2 psi per month as air permeates through the tires. 

Vehicles with underinflated tires have had handling problems that caused crashes 

resulting in fatalities and injuries. In addition, the fuel economy of vehicles driving 

on underinflated tires is slightly lower. In response to your request for information 

on these issues, we addressed the following questions: (1) What is the impact of tire 

underinflation on safety and fuel economy, and what actions has the federal 

government taken to promote proper tire inflation? and (2) what technologies are 

currently available to reduce underinflation and what are their implications for safety 

and fuel economy? 

To address these questions, we interviewed officials from federal agencies, tire 

industry associations and businesses, and public advocacy groups. We examined 

their studies on tire pressure and its impact on safety and fuel economy, and the 

technologies used to detect underinflation and maintain tire pressure. Unless 

otherwise specified, in this report we refer to the nongovernmental organizations that 

we contacted collectively as “industry.” We also examined federal legislation and 

DOT requirements on tire pressure monitoring systems (TPMS), DOT’s program for 

increasing public awareness on maintaining proper tire inflation, and fleet 

maintenance directives provided by the General Services Administration (GSA) to 

federal agencies that lease GSA vehicles. Finally, we assessed the methodology that 

NHTSA used to conduct a survey on tire underinflation and found it, and some of the 

conclusions derived by the agency from the survey, appropriate for our use in this 

report. (See encl. I for additional information on our methodology, including a list of 

 

1

NHTSA, Research Note: Tire Pressure Special Study (Washington, D.C., August 2001). 
organizations we contacted.) We conducted our work from July 2006 through 

December 2006 in accordance with generally accepted government auditing 

standards. 

Summary 

Underinflated tires impact a driver’s ability to control a vehicle against skidding, 

blowouts, and other tire failures. While not a leading cause of highway accidents and 

fatalities, a NHTSA study shows that, in 1999, underinflated tires contributed to 247, 

or 0.8 percent, of 32,061 fatalities and 23,100, or 0.8 percent, of almost 3 million 

injuries. In addition, NHTSA estimates that 41 vehicular-related deaths occur 

annually because of blowouts alone from underinflated tires. Moreover, tires that are 

not inflated to the appropriate pressure result in a slight decline in fuel economy. 

The Department of Energy’s designated economist on this issue indicated that, of the 

130 billion gallons of fuel that the Transportation Research Board (TRB)2

 estimated 

were used in passenger cars and light trucks in 2005, about 1.2 billion gallons were 

wasted as a result of driving on underinflated tires. The federal government is using 

legislation, public information, and educational programs to inform the public about 

tire underinflation. For example, the Transportation Recall Enhancement 

Accountability Documentation (TREAD) Act of 2000 required NHTSA to develop 

regulations for installing a tire pressure monitoring system in new passenger cars and 

light trucks.3

 These regulations are being phased in and will be effective for all new 

passenger cars and light trucks produced for the 2008 model year. The regulations 

will require a TPMS that will alert drivers when one or more tires are underinflated 25 

percent below the vehicle manufacturer’s recommended inflation pressure or a 

minimum pressure specified in the regulation, whichever is higher.4

 In addition, 

NHTSA works with industry to promote public awareness of the importance of 

properly inflated tires, and GSA provides information on the issue to federal agencies, 

such as DOD, that lease vehicles.

Several technologies are currently available to reduce tire underinflation, and all of 

them have the potential to increase safety and fuel economy when used 

appropriately. The federal government and industry recommend using a tire pressure 

gauge to check pressure regularly and reinflate tires to maintain proper inflation. 

Also, TPMS equipment for passenger cars and light trucks will alert drivers when a 

tire’s pressure falls 25 percent below a vehicle manufacturer’s recommended level or 

minimum activation pressure specified in the regulations, whichever is higher. When 

there is a need to increase tire pressure, consumers generally have a choice between 

two products—compressed air and nitrogen. Compressed air is readily available at 

service stations and retail tire outlets nationwide and is either free or relatively 

inexpensive for consumers. However, compressed air leaks from tires over time. 

Nitrogen permeates through tires slower than air and studies have shown that tires 

 2

The Transportation Research Board is a division of the National Research Council of the National

Academy of Sciences. See Transportation Research Board, Special Report 286: Tires and Passenger 

Vehicle Fuel Economy Informing Consumers, Improving Performance (Washington, D.C., 2006), 

http://onlinepubs.trb.org/onlinepubs/sr/sr286.pdf. 3

Public Law 106-414, 114 Stat. 1800 (2000). 4

Specifically, the regulations require that the TPMS alert drivers when one or more tires are 

underinflated 25 percent below the vehicle manufacturer’s recommended cold tire inflation pressure 

or a minimum activation pressure specified in the regulation, whichever is higher. 

Page 2 GAO-07-246R Underinflated Tires
filled with nitrogen retain pressure levels longer and age more slowly. However, 

researchers pointed out that nitrogen has not been assessed under normal driving 

conditions. Transport Canada, the Canadian government’s transportation ministry, 

has been studying the benefits of nitrogen inflation in truck tires and expects to 

complete this work in early 2007. It is unclear when the results of this work will be 

made public. NHTSA expects to complete testing on nitrogen inflation’s effects on 

the rate of loss of inflation pressure and nitrogen inflation’s effects on tire aging by 

April 2007 and March 2007, respectively. Currently, relatively few nitrogen outlets are 

available for consumers to use, and while the cost of nitrogen varies, it can exceed 

the cost of compressed air. The materials used to make tire innerliners,5

 can affect 

the amount of air and water vapor permeability. Finally, single-wide tires6

 and the 

use of pressure management and tire pressure monitoring systems on large trucks 

can also reduce the incidence of underinflated tires. 

Underinflated Tires Can Impact Vehicle Safety and Fuel Economy 

While underinflated tires are not a significant cause of highway fatalities and injuries, 

studies indicate that drivers have less control of their vehicles when tires are not 

properly inflated. In an analysis performed for the TREAD Act, NHTSA estimated 

that less than 1 percent of passenger vehicle occupant fatalities and injuries 

occurring in 1999 resulted from loss of control and skidding caused by underinflated 

tires. Specifically, 247, or 0.8 percent, of 32,061 fatalities and 23,100, or 0.8 percent, of 

almost 3 million injuries were related to underinflation. NHTSA also estimates that 

41 deaths and 1,028 injuries occur annually because of blowouts resulting from tire 

underinflation. In addition, the International Tire and Rubber Association reported 

that underinflation was the “single most common” factor in tire failure. Further, 

NHTSA reported that underinflation influences skidding, hydroplaning, increased 

stopping distance, flat tires, and blowouts. 

Underinflated tires can have a slight impact on fuel economy.7

 According to a 2006 

congressionally mandated TRB study on fuel efficiency, passenger car and light 

trucks use an estimated 130 billion gallons of fuel per year.8

 In addition, DOE’s 

designated economist on this issue estimates that vehicles with underinflated tires 

waste approximately 1.2 billion gallons of fuel per year due to the increased 

resistance of the tires.

Government Is Taking Steps to Address Tire Underinflation

The federal government has enacted legislation and is using public information and 

educational programs to inform the public about tire underinflation. Congress 

enacted the TREAD Act in 2000 in response to reports that tire failures caused by 

tread separation from certain Firestone tires installed on Ford SUVs and trucks 

 5

Innerliners are the coating laminated to the inside of tubeless tires that provide a barrier between the 

substance used to inflate the tire (e.g., compressed air) and the tire. 6

Single-wide tires are designed to replace dual-mounted tires on trucks—one single-wide tire is 

mounted on each side of an axle. 7

Other factors that affect fuel efficiency include driving habits such speeding, as well as a vehicle’s 

load. 8

TRB Special Report 286.

Page 3 GAO-07-246R Underinflated Tires
that—according to NHTSA—resulted in about 268 fatal crashes from January 1991 to 

August 2001. In addition to requiring upgrades to the agency’s safety standards for 

tires, the TREAD Act required NHTSA to develop regulations for a TPMS. In 

response, NHTSA issued a rule in 2002 that required a TPMS to be installed on new 

passenger cars and light trucks (i.e., those with a gross vehicle weight rating of 10,000 

pounds or less).9

 However, some consumer safety groups challenged NHTSA’s rule in 

court because they were concerned about whether certain types of TPMS allowed 

under the rule could sufficiently detect tire underinflation. In August 2003, a federal 

court vacated the rule and directed NHTSA to conduct further rule making that would 

be consistent with the court’s ruling.10 NHTSA subsequently issued a new rule in 2005 

that requires manufacturers to install a TPMS on all new passenger cars and light 

trucks by the 2008 model year.11 This rule, like its predecessor, is also in litigation. 

Two types of TPMS are currently available for some passenger cars and light trucks: 

direct and indirect. A direct TPMS reads a tire’s inflation pressure level with an 

electronic device mounted inside the tire either on the valve stem or the wheel, and 

sends the information via a wireless signal to a receiving unit in the vehicle. In 

contrast, an indirect TPMS checks the inflation level of a tire by monitoring the 

rotational speeds of the wheels (using the vehicle’s anti-lock braking system) and 

identifying rotational differences between the wheels. NHTSA requires both types of 

TPMS to have an indicator on the dashboard that alerts a driver if the pressure of one 

or more tires falls either 25 percent below the pressure recommended by the vehicle 

manufacturer or a minimum pressure specified in the regulation, whichever is 

higher.12 Once all new passenger vehicles and light trucks are equipped with a TPMS, 

NHTSA estimates that 119 to 121 passenger car and light truck fatalities will be 

prevented each year because it expects that 90 percent of drivers with TPMS 

technology will check and reinflate their tires in response to indications of tire 

underinflation. In addition, NHTSA estimates that this increased attention will enable 

drivers to save from $15 to $23 over the life of a vehicle because of better fuel 

economy. (See encl. II for additional information on TPMS.) 

 9

Federal Motor Vehicle Safety Standard (FMVSS) No. 138 was promulgated through a final rule

published in the Federal Register on June 5, 2002 (67 Fed Reg. 38704). 10The groups that participated in the lawsuit were Public Citizen Inc., New York Public Interest 

Research Group, and the Center for Auto Safety. Public Citizen v. Mineta, 340 F. 3d 39 (2d Cir. 2003). 11FMVSS No. 138, 70 Fed. Reg. 18136 (Apr. 5, 2005); see, also, 70 Fed. Reg. 53079 (Sept. 7, 2005) (Final

Rule; responses to petitions for reconsideration). In accordance with our policy, we did not address

the matters in litigation. 12The recommended pressure is posted on a label or placard inside the vehicle. NHTSA has developed

a table that establishes the lowest pressure levels for various tires based on tire type, a floor at which

the TPMS warning would be triggered regardless of the manufacturer’s recommended pressure level. 

Page 4 GAO-07-246R Underinflated Tires
Figure 1: Tire Pressure Monitoring Systems 

NHTSA also uses public information and educational campaigns to convey the 

importance of maintaining properly inflated tires. In 2005, for example, NHTSA 

issued brochures for a campaign it called “What’s Your PSI?” to encourage the public 

to check its tires regularly for proper inflation. NHTSA partnered with both the 

Rubber Manufacturers Association (RMA) and the American Automobile 

Association’s Motor Clubs, which distributed the brochures to members. 

Additionally, NHTSA, in conjunction with RMA, sponsors a “Tire Safety Week” during 

the last week of April each year.13 A NHTSA official told us that the agency plans to 

have public information campaigns about TPMS before the requirement becomes 

fully implemented for the 2008 model year. 

GSA, which leased about 185,000 vehicles to federal agencies in fiscal year 2005,14

provides ongoing guidance to federal fleet managers on the maintenance of their 

 13RMA also has a public awareness effort, referred to as “Be Tire Smart,” that includes brochures aimed 

at informing the public of the need to properly maintain tire pressure. 14According to GSA’s Federal Fleet Report Fiscal Year 2005, the federal fleet included more than

632,000 vehicles. GSA leases 29 percent of these vehicles to agencies, 69 percent are purchased by the 

agencies, and 2 percent are leased from commercial sources. 

Page 5 GAO-07-246R Underinflated Tires
vehicles, including suggestions for maintaining proper tire pressure.15 For example, 

in response to the President’s 2005 directive to conserve natural gas, electricity, 

gasoline, and diesel fuel after Hurricanes Katrina and Rita, GSA sent fleet customers 

fuel conservation tips that contained information on proper tire inflation. GSA does 

not operate maintenance shops of its own but instead tracks fleet vehicle 

maintenance. GSA also notifies lessees of upcoming or past-due maintenance 

requirements and follows up to assure work is completed. Agencies that lease 

vehicles from GSA are responsible for procuring maintenance and repair services 

from private vendors. They are also responsible for assuring proper tire inflation. 

According to GSA’s Director of Fleet Operations, GSA’s fees for leased vehicles are 

determined by a combination of a monthly rate and a mileage rate.16 In addition, GSA 

funds fuel and maintenance costs. However, if a vehicle’s tires wear out sooner than 

expected, or are not maintained appropriately, GSA charges the customer agency for 

the increased costs. 

The Department of Defense, with one of the largest fleets of GSA-leased vehicles, 

instituted a policy requiring users to maintain tires at the maximum pressure 

recommended by the vehicles’ manufacturers.17 Various DOD departments 

implemented this policy by requiring periodic and consistent tire inspections. For 

example, the Air Force requires vehicle operators to document tire pressure 

inspections each month at a minimum. The Navy requires vehicle operators to check 

tire pressure before using a vehicle and conduct preventive maintenance on vehicles, 

including tire pressure and tread checks, at least every 3 months, 5,000 miles, or 200 

hours of use. Similarly, the Defense Logistics Agency requires vehicle operators to 

check vehicle equipment, including tire pressure daily. 

Technologies Used to Reduce Tire Underinflation May Promote Better Fuel 

Economy and Safer Vehicle Handling 

Several technologies are currently available to reduce tire underinflation, including 

tire pressure gauges, TPMS, compressed air, nitrogen, and improved tire materials. 

Drivers of passenger cars, as well as drivers of light and heavy trucks, use tire 

pressure gauges to check tire pressure. TPMS equipment is programmed to alert 

drivers of passenger vehicles when tire pressure falls 25 percent below the level 

recommended by vehicle manufacturers or a minimum pressure set by regulation, 

whichever is higher. Compressed air and nitrogen are available to the public to 

inflate tires, and newer materials for tire innerliners and designs for truck tires will 

maintain tire pressure levels longer. In addition, tire pressure management systems 

 15GSA sells and leases passenger cars and vans; light, medium, and heavy trucks; and buses and 

emergency vehicles to customer agencies. 16All of GSA Fleet’s preventive maintenance instructions include checking tire pressure as part of the

preventive maintenance service. Additionally, GSA Fleet places in the glove box of every vehicle it 

leases to customer agencies a pamphlet entitled A Guide to Your GSA Fleet Vehicle. The pamphlet 

informs vehicle operators about proper tire care to include the importance of checking air pressure 

regularly. The pamphlet also describes for operators how to determine proper tire pressure for a 

vehicle. 17DOD, Management Acquisition and Use of Motor Vehicles, Section C12.2.5.5, from DOD 4500.36-R. 

(Washington, D.C., 1996). 

Page 6 GAO-07-246R Underinflated Tires
and central inflation systems are available to address tire underinflation on heavy 

trucks. TPMS equipment also alerts drivers of heavy trucks when tire pressure falls 

below a certain level. The basic features of each type of technology are discussed 

below. If used properly, all of the features have the potential to increase fuel 

economy and enhance vehicle safety. 

Tire Pressure Gauges 

The federal government and industry recommend that drivers of passenger vehicles 

use a tire pressure gauge to check their tire pressure at least once a month, when 

tires are cold, and inflate them to the pressure recommended by the vehicle 

manufacturer.18 (See fig. 2.) Tire industry officials indicated that large trucking fleets 

recognize this as a good practice, since tires and their maintenance represent a 

portion of their operating costs, and generally monitor their vehicles’ tire pressure on 

a more frequent basis.19 The American Trucking Association’s Technology and 

Maintenance Council also recommends that its members use quality truck tire 

pressure gauges and check them weekly against a “master gauge.” 

 18The vehicle manufacturer’s recommended pressure is posted inside the vehicle on the placard. 19Other costs are labor and fuel. 

Page 7 GAO-07-246R Underinflated Tires
Figure 2: Two Types of Tire Pressure Gauges 

Source: GAO. 

TPMS

TPMS technology will be available on all passenger vehicles starting with the 2008 

model year. According to DOT, the TPMS final rule’s phase-in has increased the 

prevalence of TPMS in the new vehicle fleet. Under the April 8, 2005 final rule, 

• 20 percent of a vehicle manufacturer’s passenger vehicles and light trucks are 

required to comply with the standard from October 5, 2005, to August 31, 2006; 

• 70 percent are required to comply from September 1, 2006, to August 31, 2007; 

and 

• all of these vehicles must comply by September 1, 2007. 

Page 8 GAO-07-246R Underinflated Tires
Although TPMS is now available on certain luxury cars and is available as optional 

equipment on large trucks, questions remain about how TPMS will operate on most 

vehicles. For example, NHTSA does not require that the TPMS identify the specific 

underinflated tire and only requires that it work with the tires originally installed by 

the vehicle manufacturer. NHTSA requires the TPMS used on passenger cars and 

light trucks to include a malfunction indicator lamp to alert the driver of the presence 

of incompatible replacement tires on the vehicle and when the TPMS is unable to 

detect low tire pressure for other reasons. 

 

Compressed Air

Compressed air, which is a combination of mostly nitrogen and oxygen,20 is 

customarily used to inflate tires and is widely available at facilities such as service 

stations and retail tire outlets. In addition, the cost of using compressed air is usually 

free or relatively inexpensive. According to some industry officials, compressed air 

permeates tires more quickly than other products such as nitrogen. However, tire 

researchers and others indicate that either product is effective if drivers check their 

tires regularly and reinflate when necessary. 

Nitrogen 

Some industry officials promote the use of nitrogen to inflate vehicle tires. Nitrogen 

permeates the rubber used in tires more slowly than air. Studies have shown that 

nitrogen retains tire pressure longer and slows tire degradation.21 However, 

according to researchers, no studies have been conducted that show the results of 

nitrogen use on safety and fuel efficiency under normal driving conditions. 

Currently, studies are being conducted on the use of nitrogen to inflate tires. A 

Canadian nitrogen manufacturer is planning to submit a report to Transport Canada, 

the Canadian government’s transportation ministry, in early 2007 on the effect of 

nitrogen inflation on fuel efficiency and costs in long-haul trucks.22 It is unclear when 

the report will be made available to the public. NHTSA is conducting two laboratory 

studies on this topic for passenger and light truck tires—one on the effects of

nitrogen inflation on the rate of loss of inflation pressure, with testing expected to be 

complete in April 2007, and another on the effects of nitrogen inflation on tire aging. 

NHTSA expects to complete testing on the tire aging study in March 2007, with public 

reports on the two studies to follow. 

 20Air is composed of 78 percent nitrogen and 21 percent oxygen. Argon and carbon dioxide make up 

the remaining 1 percent. 21For information on tire pressure retention, see Guy Walenga, Bridgestone/Firestone, Nitrogen

Inflation for Truck Tires (presented at Clemson Tire Conference, Mar. 11, 2004). For information on 

tire degradation, see Uday Karmaker, Akron Rubber Development Laboratory, Inc., Harold Herzlich, 

Herzlich Consulting, Inc., Effect of Nitrogen Purity on the Oxidation of Belt Coat Compound

(presented at International Tire Exhibition and Conference 2006, Akron, Ohio); and John M. Baldwin, 

David R. Bauer, Kevin, R. Ellwood, Ford Motor Co., Effects of Nitrogen Inflation on Tire Aging and 

Performance (conference paper, May 2004). 22The study was originally undertaken to evaluate technologies to reduce greenhouse gases.

Page 9 GAO-07-246R Underinflated Tires
Two challenges affecting the widespread use of nitrogen in passenger cars and light 

truck tires include the lack of infrastructure that would make it readily available to 

consumers and the cost of filling tires. According to federal and industry officials, 

researchers, and public safety advocates, most service stations and tire retailers do 

not have nitrogen pumps or generators. Retailers such as Costco and some Sam’s 

Club locations are exceptions and currently offer nitrogen, at no cost, to their 

members when they purchase tires. Since other retailers offer nitrogen on a more 

limited basis nationwide, and the cost of using it varies depending on the retailer or 

the location, we could not reliably determine the average cost of filling a tire. 

Industry officials indicated that some retailers may purge air from a vehicle’s tires

and replace it with nitrogen at no cost while others may charge prices ranging from 

$20 to $79 per vehicle.23

 

Tire Innerliners 

Tire manufacturers can select from a variety of materials to make tire innerliners—

the coating laminated to the inside of tires. The type of material selected determines 

the amount of air and water vapor that permeates a tire and causes it to deflate and 

degrade. Currently, the tires most often available to consumers include innerliners 

that are made from varying blends of synthetic rubber polymers (known as 

halobutyls) and other types of rubber. Tire researchers and experts have shown that 

innerliners made from high ratios of bromobutyl, one type of halobutyl, are the least 

permeable to air and water vapor and best able to retain pressure. However, 

innerliners made from high ratios of this material are more expensive than those 

made with high ratios of natural and synthetic rubbers and, according to researchers, 

are more likely found in original equipment tires than replacement tires. 

 

Truck Tire Design and Inflation Systems

Improvements in heavy truck tire testing and central inflation systems have the 

potential to reduce tire underinflation and increase fuel economy. Single-wide tires 

have replaced dual tires on some large trucks and tractor trailers. According to the 

Environmental Protection Agency (EPA), single-wide tires could improve fuel 

economy by up to 4 percent because they have less rolling resistance and weight. 

According to DOT, single-wide tires also reduce by half the number of points to check 

and tires to inflate, significantly reducing the time needed to check tire pressure on a 

tractor-trailer combination vehicle. Tire pressure monitoring systems can provide an 

early warning of air pressure loss before a tire sustains damage. Single-wide tires 

also present several disadvantages that involve transition costs for fleets and their 

potential damage to highway pavement (see encl. III). In addition, central inflation 

systems on trucks can continually monitor and adjust the amount of inflation 

pressure in tires while the vehicle is in motion. According to officials from the EPA 

and the Federal Motor Carrier Safety Administration, these systems could also 

improve fuel economy. (See encl. III for further discussion of these technologies.) 

 23Because of the relative lack of studies showing the impact of nitrogen on fuel economy, and the 

varying costs cited for inflating tires with nitrogen, we did not determine the extent to which the 

increased cost for inflating tires may be offset by lower fuel costs and a less frequent need to purchase

replacement tires. 

Page 10 GAO-07-246R Underinflated Tires
Agency Comments 

We provided copies of a draft of this report to the Departments of Transportation, 

Defense, and Energy; the General Services Administration; and the Environmental 

Protection Agency. Their technical comments have been incorporated into the 

report, as appropriate. 

----------------------------------------------------------------- 

As agreed with your office, unless you publicly announce the contents of this report 

earlier, we plan no further distribution until 30 days from the report date. At that 

time, we will send copies to other interested congressional committees. We will also 

make copies available to others upon request. In addition, the report will be available 

at no charge on GAO’s Web site at http://www.gao.gov. 

If you or your staff have any questions about this report, please contact me at (202) 

512-6570 or siggerudk@gao.gov. Contact points for our Offices of Congressional 

Relations and Public Affairs may be found on the last page of this report. Individuals 

making key contributions to this report are listed in enclosure IV. 

Sincerely yours, 

Katherine A. Siggerud 

Director, Physical Infrastructure Issues 

Enclosures 

Page 11 GAO-07-246R Underinflated Tires
Enclosure I: Scope and Methodology 

We obtained information on a variety of issues involving passenger and truck tires in 

the United States by interviewing officials, and examining the documents they 

provided, with the federal agencies, tire and automotive industries, businesses, and 

public safety advocacy groups shown in table 1. Officials with the Department of 

Transportation’s (DOT) National Highway Traffic Safety Administration (NHTSA) 

and Federal Motor Carrier Safety Administration (FMCSA) provided documents on 

their public information efforts to encourage the public to regularly check their tires 

for proper inflation; data on accidents and fatalities caused by underinflated tires; 

analyses developed for the tire pressure monitoring system (TPMS) regulations; and 

information about ongoing studies on tires. Officials with the public safety advocacy 

groups and some industries provided their views on TPMS regulations. In addition, 

we reviewed NHTSA’s survey of tire pressures in passenger vehicles and studies on 

tire safety. The General Services Administration provided information on its vehicle 

leasing program, including details on maintenance as a factor in agencies’ lease rates. 

We obtained information on the role that civilian and military Department of Defense 

employees have in maintaining appropriate tire pressure levels for vehicles in its 

fleet. The Department of Energy, Environmental Protection Agency, National 

Academy of Sciences’ Transportation Research Board, Akron Rubber Development 

Laboratory, and the business groups provided information and data on using 

compressed air and nitrogen to inflate tires, and the impact on safety and fuel 

economy of each product. We also obtained information from industry associations 

on their initiatives to alert the public on tire inflation. 

Industry officials provided information on the materials used to make and inflate tires 

and the impact that a TPMS will have on tires. The public advocacy groups provided 

information on the impact that a TPMS may have on tire safety. 

We received information from some organizations listed in table 1 on the 

technologies currently available to reduce underinflation and their implications for 

fuel economy and safety. In addition, we interviewed manufacturers (e.g., IngersollRand) that produce nitrogen generation equipment for tire inflation to determine why 

they believe it is a better product for inflating tires, as well as retailers (e.g., Costco) 

that offer both nitrogen and compressed air to consumers. We also obtained 

comments from officials we interviewed on the reliability, safety, cost effectiveness, 

and fuel efficiency of compressed air and nitrogen to inflate tires. We performed our 

work from July 2006 through December 2006 in accordance with generally accepted 

government auditing standards. 

Page 12 GAO-07-246R Underinflated Tires
Table 1: Organizations Contacted during Our Review

Federal organizations

Department of Transportation (NHTSA and FMCSA) 

Department of Defense 

Department of Energy 

General Services Administration 

Environmental Protection Agency 

Industry associations 

Rubber Manufacturers Associationa 

American Trucking Association 

American Automobile Association 

Alliance of Automobile Manufacturersb 

Tire Industry Association 

Tire Retread Information Bureau

Businesses 

Ford Motor Company 

Roush Racing 

NASCAR 

American Airlines 

Akron Rubber Development Laboratory 

Ingersoll-Rand

Branick Industries 

Parker Hannifin

Schrader-Bridgeport 

EnTire Solutions 

Costco 

Wal-Mart 

Discount Tire Company 

Tire Kingdom 

Public advocacy organizations

Center for Auto Safety 

Advocates for Highway and Auto Safety 

Public Citizen 

Source: GAO. a

Representatives from Bridgestone, Continental, Goodyear, Michelin, and Pirelli tire companies participated in this meeting. b

Representatives from General Motors and Daimler Chrysler participated in this meeting.

Page 13 GAO-07-246R Underinflated Tires
Enclosure II: Tire Pressure Monitoring Systems 

NHTSA requires all new 2008 model year passenger cars and light trucks to have a 

tire pressure monitoring system (TPMS) to alert drivers when the pressure in one or 

more tires falls 25 percent below the vehicle manufacturer’s recommended inflation 

pressure or a minimum activation pressure specified by NHTSA, whichever is 

higher.24 NHTSA also requires the TPMS to include a malfunction indicator that alerts 

drivers when the TPMS is not functioning because of either a system failure or the 

placement of incompatible replacement tires on the vehicles. 

Industry developed two types of TPMS—direct and indirect. A direct TPMS uses an 

electronic device mounted either on the valve stem or the inside of a wheel to read 

inflation pressure. It sends a wireless signal about a tire’s inflation level to a 

receiving unit that alerts the driver through a warning light on the dashboard if tire 

pressure falls below a certain threshold.25 An indirect TPMS uses a vehicle’s existing 

anti-lock braking system equipment to monitor the rotational speeds of the wheels. 

When it detects a difference in rotational speed in one wheel compared with the 

others, the system infers that a tire is underinflated and alerts the driver through a 

visual alarm. 

Industry and public safety advocacy groups have expressed concern about the 

capabilities of TPMS as it relates to NHTSA’s requirements. For example, a tire 

industry official said that if replacement tires not compatible with the TPMS are 

installed, NHTSA regulations require that the malfunction indicator lamp illuminate 

to alert the driver that the TPMS cannot detect underinflation.26 In such cases, the 

owner would have to replace the new equipment for tires or wheels that are 

compatible with the TPMS. According to DOT, however, available data suggest that 

only a very small number of replacement tires are likely to generate problems for 

TPMS, although it has not been possible to identify problematic tires based on size or 

construction characteristics. Although DOT officials claim that vehicle 

manufacturers report few warranty claims based on instances of replacement tires 

being incompatible with a TPMS, we think that conclusions about this area should 

wait until after 2008, when more vehicles are equipped with a TPMS. 

At the time of our review, no indirect TPMS has been marketed that meets NHTSA’s 

requirement to identify one to four underinflated tires at a time. Further, the indirect 

TPMS cannot detect underinflation when all four tires are equally underinflated. An 

indirect TPMS is considered the least expensive option, however, because it requires 

less additional hardware on vehicles equipped with anti-lock brakes. As previously 

noted, NHTSA’s current rule is in litigation. In accordance with our policy, we 

neither included in our objectives nor addressed matters in litigation. 

 24FMVSS No. 138. 70 Fed. Reg. 18136 (April 5, 2005); see, also, 70 Fed. Reg. 54079 (Sept. 7, 2005), “Tire 

Pressure Monitoring Systems.” 

25Although NHTSA requires that the alert be triggered when pressure falls 25 percent below the vehicle 

manufacturer’s recommended level, some TPMS, depending on the manufacturer, will trigger alerts 

earlier. 26NHTSA requires that original equipment manufacturers certify TPMS on the tires installed on the

vehicle at the time of the initial vehicle sale. 

Page 14 GAO-07-246R Underinflated Tires
Enclosure III: New Tire Designs and Technologies for Heavy Trucks Offer 

Enhanced Safety and Improved Fuel Economy 

Several recent innovations in truck tire and wheel technology are designed to 

enhance fuel economy and also offer safety benefits. For example, single-wide tires27

are designed to replace traditional dual-mounted tires on trucks—one single-wide tire 

is mounted on each side of an axle. Single-wide tires can be used for all tractor and 

trailer tire positions except for the steer tires at the front of the tractor. Using singlewide tires, a traditional 18-wheel tractor-trailer, with 2 steer tires, 4 pairs of drive 

tires, and 4 pairs of trailer tires, would have a total of only 10 tires—2 steer tires, 4 

drive tires, and 4 trailer tires. According to the EPA’s SmartWay Transport 

Partnership,

28 the reduced rolling resistance and weight of the tires and wheels could 

improve fuel economy by up to 4 percent.29 According to DOT, single-wide tires also 

reduce by half the number of points to check and tires to inflate, significantly 

reducing the time needed to check tire pressure on a tractor-trailer combination

vehicle. Similarly, the American Trucking Association (ATA) noted that single-wide 

tires effectively eliminate the problem of checking inflation pressure on the inner 

dual-mounted tire. Additionally, tire pressure monitoring systems can provide an 

early warning of air pressure loss before a tire sustains damage. 

ATA noted, however, that single-wide tires present several disadvantages. For 

example, transition costs might pose a challenge, since fleets would have to maintain 

two sets of wheel hardware until the entire fleet was converted. Another 

disadvantage is the potential damage to pavement. According to ATA and Virginia 

Tech’s Transportation Institute, the first generation of single-wide tires damaged 

pavement at a greater rate than dual-mounted tires.30 However, as the design of 

single-wide tires has evolved, the tires have become increasingly wider. According to 

a FMCSA official, wider tires distribute the load over a greater area, reducing the 

impact on the pavement. These experts also say that potential for pavement damage 

from the newest generation of single-wide tires is comparable with conventional dualmounted tires. A potential disadvantage, according to DOT, involves the safety of the 

truck if one of the single-wide tires fails. In contrast, when one of a pair of dualmounted tires fails, there is still another tire available. 

Central inflation systems are another technology for trucks to reduce underinflation. 

These systems can monitor and continually adjust the inflation pressure in tires, even 

while the truck is in motion. Two main types of systems are currently available. One 

system uses the truck’s existing air-brake compressor to supply air to tires. Another 

uses self-contained compressors on each hub that generate compressed air through 

 27Also known as “super-singles” or “wide-base” tires, single-wide tires have been used on trucks in 

Europe and Canada since the early 1980s. A distinction should be made between first generation 

“super-single” tires, which were introduced in the 1980s and “new generation” super-singles” tires. 28EPA’s SmartWay Transport Partnership is a voluntary collaboration between U.S. EPA and the freight 

industry designed to increase energy efficiency while significantly reducing greenhouse gases and air 

pollution. 29This assumes single-wide tires are mounted using weight-saving aluminum rims on all applicable

axles of the tractor and the trailer. 30I. L. Al-Qadi, M. Elseifi, and P.J. Yoo, Virginia Tech Transportation Institute, Pavement Damage Due 

to Different Tires and Vehicle Configurations (Blacksburg, Virginia, May 2004); and Jim Tipka, 

American Trucking Institute, New Generation Wide Based Single Tires (June 2006). 

Page 15 GAO-07-246R Underinflated Tires
the rolling motion of the wheels. According to FMCSA, central inflation systems 

could offer significant savings to fleet operators by improving fuel economy and 

safety. According to EPA’s SmartWay Transport Partnership, these systems could 

annually save long-haul trucks up to $200 in tire maintenance costs, and $170 in fuel 

costs per truck. However, these systems also present several disadvantages. For 

example, according to an ATA official, systems operating from the air-brake 

compressor involve an extensive array of tubing and valves, increasing the potential 

for leaks. 

Page 16 GAO-07-246R Underinflated Tires
Enclosure IV: GAO Contact and Staff Acknowledgments

GAO Contact 

Katherine Siggerud, (202) 512-6570 or siggerudk@gao.gov 

Staff Acknowledgments 

In addition to the contact named above, Nabajyoti Barkakati, Lindsay Bach, Colin 

Falon, Jay Cherlow, Lynn Filla-Clark, H. Brandon Haller, Phillis Riley, Karla Springer, 

Don Watson, and Mindi Weisenbloom made key contributions to this report. 

(542094) 

Page 17 GAO-07-246R Underinflated Tires
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