Underinflated Tires in the United States (09-FEB-07,
GAO-07-246R).
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?
-------------------------Indexing Terms-------------------------
REPORTNUM: GAO-07-246R
ACCNO: A65806
TITLE: Underinflated Tires in the United States
DATE: 02/09/2007
SUBJECT: Accident prevention
Fuel consumption
Motor vehicle standards
Motor vehicles
Statistical data
Traffic accidents
Transportation legislation
Transportation safety
Public safety
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GAO-07-246R
* [1]PDF6-Ordering Information.pdf
* [2]Order by Mail or Phone
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 organizations we contacted.) We conducted our work from July 2006
through December 2006 in accordance with generally accepted government
auditing standards.
1NHTSA, Research Note: Tire Pressure Special Study (Washington, D.C.,
August 2001).
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
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.
2The 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),
[3]http://onlinepubs.trb.org/onlinepubs/sr/sr286.pdf .
3Public Law 106-414, 114 Stat. 1800 (2000).
4Specifically, 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.
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 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.
5Innerliners 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.
6Single-wide tires are designed to replace dual-mounted tires on
trucks--one single-wide tire is mounted on each side of an axle.
7Other factors that affect fuel efficiency include driving habits such
speeding, as well as a vehicle's load.
8TRB Special Report 286.
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.)
9Federal 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.
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 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.
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.
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
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.
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).
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.
Figure 2: Two Types of Tire Pressure Gauges
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,
o 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;
o 70 percent are required to comply from September 1, 2006, to
August 31, 2007; and
o 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,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.
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.
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 [email protected] . 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
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
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.
aRepresentatives from Bridgestone, Continental, Goodyear, Michelin, and
Pirelli tire companies participated in this meeting.
bRepresentatives from General Motors and Daimler Chrysler participated in
this meeting.
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.
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 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,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 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. Enclosure IV: GAO Contact and Staff Acknowledgments
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).
Enclosure IV: GAO Contact and Staff Acknowledgments
GAO Contact
Katherine Siggerud, (202) 512-6570 or [email protected]
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)
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