Underinflated Tires in the United States
Gao ID: GAO-07-246R February 9, 2007
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). 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 a Congressional 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?
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 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. These regulations are being phased in and will be effective for all new passenger cars and light trucks produced for the 2008 model year. 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, tire pressure monitoring systems (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. 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, 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.
GAO-07-246R, Underinflated Tires in the United States
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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.
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)[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:
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.
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.[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
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.)
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 [Hyperlink, 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,
Signed by:
Katherine A. Siggerud:
Director, Physical Infrastructure Issues:
Enclosures:
[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
standards.
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.
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.
[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
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.[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
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.[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 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):
FOOTNOTES
[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,
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.
[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
pollution.
[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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