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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).[Footnote 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 organizations we contacted.) We 
conducted our work from July 2006 through December 2006 in accordance 
with generally accepted government auditing standards. 


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)[Footnote 
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.[Footnote 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.[Footnote 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 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,[Footnote 5] can affect the 
amount of air and water vapor permeability. Finally, single-wide 
tires[Footnote 6] 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.[Footnote 
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.[Footnote 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 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).[Footnote 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.[Footnote 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.[Footnote 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.[Footnote 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.) 

Figure 1: Tire Pressure Monitoring Systems: 

[See PDF for Image] 

Source: GAO. 

[End of Figure] 

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.[Footnote 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,[Footnote 14] provides ongoing guidance to federal fleet 
managers on the maintenance of their vehicles, including suggestions 
for maintaining proper tire pressure.[Footnote 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.[Footnote 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.[Footnote 
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 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.[Footnote 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.[Footnote 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." 

Figure 2: Two Types of Tire Pressure Gauges: 

[See PDF for Image] 

Source: GAO. 

[End of Figure] 


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. 

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,[Footnote 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. 


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.[Footnote 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.[Footnote 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. 

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.[Footnote 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 

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.) 

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 

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 [Hyperlink,]. 

If you or your staff have any questions about this report, please 
contact me at (202) 512-6570 or 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, 

Signed by: 

Katherine A. Siggerud: 
Director, Physical Infrastructure Issues: 


[End of section] 

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., Ingersoll-Rand) 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 

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: 
Industry associations. 
Rubber Manufacturers Association[A]. 
American Trucking Association. 
American Automobile Association. 
Alliance of Automobile Manufacturers[B]. 
Tire Industry Association. 
Tire Retread Information Bureau. 

Ford Motor Company. 
Roush Racing. 
American Airlines. 
Akron Rubber Development Laboratory. 
Branick Industries. 
Parker Hannifin. 
EnTire Solutions. 
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. 

[End of table] 

[End of section] 

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.[Footnote 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 

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.[Footnote 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.[Footnote 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. 

[End of section] 

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 tires[Footnote 27] 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 single-wide 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,[Footnote 28] the reduced rolling 
resistance and weight of the tires and wheels could improve fuel 
economy by up to 4 percent.[Footnote 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 

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.[Footnote 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 dual-mounted 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 dual-mounted 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 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. 

[End of section] 

Enclosure IV: GAO Contact and Staff Acknowledgments: 

GAO Contact: 

Katherine Siggerud, (202) 512-6570 or 

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. 



[1] NHTSA, Research Note: Tire Pressure Special Study (Washington, 
D.C., August 2001). 

[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), [Hyperlink,]. 

[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. 

[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. 

[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). 

[10] The 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). 

[11] FMVSS 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. 

[12] The 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. 

[13] RMA 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. 

[14] According 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. 

[15] GSA sells and leases passenger cars and vans; light, medium, and 
heavy trucks; and buses and emergency vehicles to customer agencies. 

[16] All 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. 

[17] DOD, Management Acquisition and Use of Motor Vehicles, Section 
C12.2.5.5, from DOD 4500.36-R. (Washington, D.C., 1996). 

[18] The vehicle manufacturer's recommended pressure is posted inside 
the vehicle on the placard. 

[19] Other costs are labor and fuel. 

[20] Air is composed of 78 percent nitrogen and 21 percent oxygen. 
Argon and carbon dioxide make up the remaining 1 percent. 

[21] For 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). 

[22] The study was originally undertaken to evaluate technologies to 
reduce greenhouse gases. 

[23] Because 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. 

[24] FMVSS No. 138. 70 Fed. Reg. 18136 (April 5, 2005); see, also, 70 
Fed. Reg. 54079 (Sept. 7, 2005), "Tire Pressure Monitoring Systems." 

[25] Although 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. 

[26] NHTSA requires that original equipment manufacturers certify TPMS 
on the tires installed on the vehicle at the time of the initial 
vehicle sale. 

[27] Also 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. 

[28] EPA'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 

[29] This assumes single-wide tires are mounted using weight-saving 
aluminum rims on all applicable axles of the tractor and the trailer. 

[30] I. 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).  

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