Transportation:

Underinflated Tires in the United States

GAO-07-246R: Published: Feb 9, 2007. Publicly Released: Mar 5, 2007.

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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.

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