Report to the Chairman and Ranking

Minority Member, Committee on

Commerce, Science, and

Transportation, U.S. Senate

United States General Accounting Office

GAO

June 2001 VEHICLE SAFETY

Technologies,

Challenges, and

Research and

Development

Expenditures for

Advanced Air Bags

GAO-01-596
Page i GAO-01-596 Vehicle Safety

Letter 1

Appendix I Scope and Methodology 23

Appendix II Selected Aspects and Status of the Advanced Air Bag

Rule 24

Appendix III Multistage Frontal Air Bag Systems in Model

Year 2001 Vehicles and Model Year 2002 Vehicles in

Production as of April 1, 2001 33

Appendix IV Current Availability of and Anticipated Improvements

in Advanced Air Bag Technologies 37

Tables

Table 1: Current Availability of Advanced Air Bag Technologies and

Planned Improvements to Comply With Advanced Air Bag

Rule 8

Table 2: NHTSA Expenditures on R&D for Advanced Air Bag

Technologies, Fiscal Years 1998-2001 20

Figures

Figure 1: Air Bag Fatalities, by Type of Occupant and Belted Status,

as of April 2001 5

Figure 2: Comparison of Conventional and Advanced Frontal Air

Bag Systems 9

Figure 3: Percentage Change in Four Vehicle Manufacturers’

Advanced Air Bag R&D Expenditures, 1999 Through 2004 21

Contents
Page ii GAO-01-596 Vehicle Safety

Figure 4: Test Options in the Advanced Air Bag Rule to Meet

Suppression and Low-Risk Deployment Requirements for

Smaller Occupants 25

Figure 5: Tests Required in the Advanced Air Bag Rule to Improve

Protection for Occupants of Different Sizes 28

Figure 6: Timeline for Phase-in of Requirements in the Advanced

Air Bag Rule 29

Abbreviations

NHTSA National Highway Traffic Safety Administration

R&D research and development
Page 1 GAO-01-596 Vehicle Safety

June 12, 2001

The Honorable Ernest F. Hollings

Chairman

The Honorable John McCain

Ranking Minority Member

Committee on Commerce, Science,

 and Transportation

United States Senate

Air bags can help save lives in frontal crashes, especially when used with

seat belts. However, the power of a deploying air bag can also injure or kill

people. According to the National Highway Traffic Safety Administration

(NHTSA), an estimated 6,856 lives have been saved by air bags, but 175

fatalities—primarily children and small women—have been attributed to

the deployment of an air bag in relatively low-speed crashes as of April

2001. Concerned about these fatalities, the Congress directed the

Secretary of Transportation in 1998 to require vehicle manufacturers to

install advanced air bag systems. Advanced air bag systems tailor the

deployment of the bags to the characteristics of the occupant and different

levels of crash severity. On May 12, 2000, NHTSA issued a rule requiring

vehicle manufacturers to install these systems in an increasing number of

vehicles over several years beginning September 1, 2003.

You asked us to report on the development of technologies that vehicle

manufacturers plan to use to comply with the advanced air bag rule.

Accordingly, we examined the (1) current availability of and planned

improvements to advanced air bag technologies; (2) challenges, if any, that

the industry faces in complying with the rule; and (3) changes in federal

and industry expenditures on the research and development (R&D) of

advanced air bag technologies since 1998.

To address these issues, we met with representatives from eight

companies that manufacture vehicles and five companies that supply air

bag systems to these manufacturers. We chose the manufacturers—BMW,

DaimlerChrysler, Ford, General Motors, Honda, Nissan, Toyota, and

Volkswagen—because, according to the Alliance for Automobile

Manufacturers, their combined sales account for over 90 percent of

vehicles sold in the United States. We chose the air bag suppliers—Autoliv,

Breed, Delphi, Takata, and TRW—because they are the primary suppliers

of air bag systems for vehicles sold in the United States. We also met with

officials from NHTSA, representatives from the Insurance Institute for

Highway Safety, the National Transportation Safety Board, university

United States General Accounting Office

Washington, DC 20548
Page 2 GAO-01-596 Vehicle Safety

researchers, and consumer groups. For the changes in industry

expenditures on advanced air bag R&D, an industry association provided

information aggregated from four manufacturers. We did not verify this

aggregated information because individual vehicle manufacturers consider

their R&D expenditure information confidential. (See app. I for a detailed

discussion of how we conducted our work.)

Some advanced air bag technologies are currently being installed in

vehicles and others are still being developed. The principal advanced

technology that is currently being installed in some vehicles is air bags that

can inflate with lower or higher levels of power—rather than a single

level—depending on the severity of the crash. For example, four

manufacturers installed frontal air bag systems that can deploy with

multiple levels of power in at least 25 percent of their model year 2001

vehicles. Some manufacturers have also installed other advanced

technologies, such as sensors that enable the air bag system to adapt its

deployment for belted or unbelted occupants or for drivers who are seated

close to the steering wheel. Although frontal air bag systems with these

advanced technologies represent improvements over previous systems,

they do not contain all of the features that manufacturers believe are

needed to meet the requirements in the advanced air bag rule, such as

sensors that can distinguish among different types of occupants. To meet

the requirements, manufacturers plan to introduce new technologies as

well as continue to make further improvements in current technologies.

The key new technologies that manufacturers plan to introduce are

occupant classification sensors that can distinguish among infants and

children (as well as their safety seats), and adults on the passenger side.

The addition of these sensors is necessary to allow the air bag system to

provide the appropriate deployment level—such as no deployment, low

power, or high power—depending on the type of occupant.

The primary challenge in meeting the requirements in the advanced air bag

rule is the development of occupant classification sensors that are

accurate, durable, and suitable for mass production. Sensors that are

currently being developed sometimes classify an occupant inaccurately,

which could result in the air bag not deploying when it should, deploying

when it should not, or deploying with greater or less force than intended.

In addition, occupant classification sensors have not demonstrated the

ability to operate reliably over the presumed 15-year life of a vehicle or to

be consistently produced and integrated into vehicles in large quantities.

Vehicle manufacturers are working with air bag suppliers to overcome

these problems and plan to introduce these sensors in some of their

vehicles by September 2003, as required. However, the development of

Results in Brief
Page 3 GAO-01-596 Vehicle Safety

occupant sensing technologies is taking longer than anticipated. For

example, some manufacturers previously anticipated that occupant

classification sensors would be installed in model year 2000 vehicles.

These sensors were not sufficiently developed for installation at that time,

and some manufacturers told us that these sensors have still not reached

the level of development that a new technology should have reached to be

ready by the September 2003 deadline—just over 2 years away. NHTSA

and vehicle manufacturers have discussed these issues but, as of April

2001, none of the manufacturers have told NHTSA they will be unable to

meet the deadline. Due to the uncertainty associated with developing

occupant classification sensors, NHTSA officials told us they plan to stay

abreast of manufacturers’ progress by maintaining communications with

manufacturers and conducting research on the feasibility of occupant

classification technologies.

Expenditures on advanced air bag R&D by NHTSA and vehicle

manufacturers have increased since 1998, when the Congress mandated

the installation of advanced air bags in future vehicles. NHTSA’s reported

expenditures increased from about $6.3 million in fiscal year 1998 to

nearly $7.0 million in fiscal year 2000. This spending was primarily for

activities related to the development of the advanced air bag rule, such as

investigations of real-world crashes and studies to determine how people

are injured or killed by air bags. NHTSA’s expenditures are expected to

increase to $7.2 million in fiscal year 2001 to, among other things, monitor

the performance of advanced air bags and develop specific advanced air

bag technologies. Individual vehicle manufacturers did not provide

information on their expenditures because they consider this information

confidential. Instead, four manufacturers coordinated through an industry

association to provide aggregated information on their advanced air bag

R&D expenditures, such as staffing, developing technology, building test

facilities and conducting tests, and integrating technologies into vehicles.

According to the industry association, these expenditures generally total

between $20 million and $30 million per vehicle “platform” (a group of

vehicles that utilize the same basic design). The information aggregated

from the four manufacturers shows that these expenditures increased by

about 275 percent from 1998 through 2000 and are anticipated to increase

overall by about 375 percent from 1998 through 2003, when the

requirements in the advanced air bag rule take effect.

In commenting on a draft of this report, the Department of Transportation

offered only one technical comment on the availability of occupant

classification sensors. We verified that the information in our draft report

was accurate and therefore did not change it.
Page 4 GAO-01-596 Vehicle Safety

Air bags are one part of a vehicle’s occupant protection system, which also

includes the structure of the vehicle and seat belts. Seat belts are the

primary restraint for an occupant during a crash, and air bags are intended

to supplement this protection. In 1999, NHTSA reported that seat belt use

alone (lap and shoulder belts) reduces fatalities by 45 percent in crashes

involving an impact to the front of the vehicle, frontal air bags without seat

belts reduce fatalities by 14 percent, and the combination of seat belts and

air bags reduces fatalities by 50 percent.1

Between 1986 and April 2001, frontal air bags have saved an estimated

6,856 lives but have caused 175 fatalities that have been confirmed by

NHTSA—19 infants in a rear-facing child seat, 85 children (not in a rearfacing child seat), 64 drivers, and 7 adult passengers—in relatively lowspeed crashes.2

 NHTSA investigators have found that people who were

killed by deploying air bags were typically in close proximity to the air bag

in one of two ways:

• The occupant was thrown forward by events that occurred before the air

bag deployed, such as sudden braking immediately before the crash or

multiple impacts. This usually occurred because the occupant was

unbelted or improperly belted.

• The occupant’s initial seating position placed them close to the air bag.

According to NHTSA, these fatalities included shorter drivers who were

belted but had moved the seat forward in order to more easily reach the

steering wheel and pedals, infants in rear-facing child seats, and children

sitting on the lap of another passenger.

The majority of people who were killed by deploying air bags in low-speed

crashes were unbelted or improperly restrained, which made them more

susceptible to being thrown into the path of the deploying air bag than

belted occupants. (See fig. 1.)

 1

Fourth Report to Congress: Effectiveness of Occupant Protection Systems and Their Use,

NHTSA, May 1999.

2

As of April 2001, NHTSA is investigating an additional 61 unconfirmed air bag-related

fatality cases: 1 infant in a rear-facing child seat, 43 children (not in a rear-facing child

seat), 12 drivers, and 5 adult passengers. According to NHTSA, about 90 percent of

unconfirmed cases are eventually confirmed.

Background
Page 5 GAO-01-596 Vehicle Safety

Figure 1: Air Bag Fatalities, by Type of Occupant and Belted Status, as of April 2001

Note: Child fatalities in rear-facing infant seats are not considered “properly restrained” because

children in a rear-facing infant seat should not be placed in a front seat with a passenger air bag.

Source: NHTSA.

The reported number of air bag-related fatalities increased from 1 in 1990

to 58 in 1997, as the installation of air bags in vehicles increased.3

 Since

1997, the number of fatalities has decreased; 17 fatalities were reported in

2000.4

 NHTSA attributes the decrease in part to actions that resulted from

its November 1996 plan to address the risk of air bag-related fatalities.

These actions included a public education effort to persuade people to

properly restrain infants and children under 12 in the rear seat and issuing

 3

In September 1993, NHTSA required vehicle manufacturers to install air bags in all

passenger cars beginning in model year 1998, and in all light trucks beginning in model year

1999. According to NHTSA, vehicle manufacturers installed air bags in advance of the

federal requirements.

4

Reported fatalities include confirmed and unconfirmed cases.
Page 6 GAO-01-596 Vehicle Safety

a rule in March 1997 that made it possible for manufacturers to quickly

reduce the inflation power in the air bags installed in new vehicles. From

model year 1997 through 1998, manufacturers lowered the inflation power

by an average of 22 percent in driver-side air bags and 14 percent in

passenger-side air bags.5

 NHTSA’s 1996 plan also anticipated the need for

long-term technological improvements—advanced air bag systems—to

control or prevent deployment of the air bag, as appropriate.

In June 1998, the Transportation Equity Act for the 21st Century directed

the Secretary of Transportation to issue a rule requiring vehicle

manufacturers to install advanced air bag systems. The act specified that

these systems should achieve two goals—provide improved protection for

occupants of different sizes (belted and unbelted) as well as minimize the

risk of injury or death from air bags for infants, young children, and other

occupants. On May 12, 2000, NHTSA issued a rule specifying the

requirements for such a system. Under the previous requirements, vehicle

manufacturers performed tests that involved crashing vehicles into a rigid

barrier with crash dummies—belted and unbelted—that represented

average-sized males in the driver and passenger seats.6

 To provide

improved crash protection for occupants of different sizes, the rule adds

new crash tests that simulate different types of crashes and include the

use of crash dummies that represent small adults (defined as a 5th

percentile female).7

 To reduce the risk of injury or death to children and

small adults, the rule requires a new battery of “static” tests using

dummies representing infants, young children, and 5th percentile females.

These tests involve placing the dummy in various positions in the seat to

determine if the air bag system suppresses or activates the air bag, or

placing the dummy against the air bag module and deploying the air bag to

determine if the bag deploys in a “low-risk” manner that does not cause

severe injury. Starting in the production year beginning September 1, 2003

 5

As of April 2001, NHTSA has found that depowered air bags appear to be as effective as

previous air bags in protecting occupants, including larger occupants in medium- to highspeed crashes.

6

NHTSA’s March 1997 rule allowed manufacturers the option of certifying the performance

of air bag systems using a “sled test” rather than crashing the vehicle into a rigid barrier. A

sled test involves placing a vehicle on a “sled-on-rails” and accelerating the sled and vehicle

very rapidly backward.

7

Crash dummies do not sufficiently represent the human physiology, so the rule allows the

use of appropriately sized humans to test the performance of the technologies in static

suppression tests.
Page 7 GAO-01-596 Vehicle Safety

(approximately model year 2004)8 and continuing over a 3-year phase-in

period, increasing percentages of each manufacturer’s vehicles must

comply with the requirements of the rule.9

 (See app. II for a more

comprehensive discussion of the rule’s requirements.)

Manufacturers have installed some of the advanced technologies that will

be needed to comply with the advanced air bag rule in certain vehicles that

are on the market today. (See table 1.) Manufacturers and companies that

produce air bags are working on the development of other needed

advanced technologies, with the aim of having them ready for installation

in vehicles by September 2003, as required.

 8

The timing of the model year varies from company to company, but generally begins

between August and October.

9

The rule will be phased in during two stages. During the first stage phase-in—from

September 1, 2003, to August 31, 2006—an increasing number of each manufacturer’s

vehicles must be certified each year as passing all of the requirements in the advanced air

bag rule. During the second stage phase-in—from September 1, 2007, to August 31, 2010—

the speed for one of the tests (the belted test for the 50th percentile adult male dummy)

will be increased from 30 to 35 miles per hour. As with the earlier requirements, an

increasing percentage of vehicles must comply with the new test speed each year.

Some Advanced

Technologies Are

Available; Others Are

Being Developed
Page 8 GAO-01-596 Vehicle Safety

Table 1: Current Availability of Advanced Air Bag Technologies and Planned Improvements to Comply With Advanced Air

Bag Rule

Component of

advanced air bag

system Advanced technologies currently available

Improvements planned to comply with advanced air

bag rule

Occupant

classification

sensors

Some vehicles with multistage air bags have one or

more of the following:

• Driver and passenger seat belt usage sensors

• Driver seat position sensors

• Sensors to detect the presence of an occupant in

the passenger seat

• Increased use of seat belt usage and seat position

sensors.

• Weight-based or pattern-based sensors that can

identify the type of occupant in the passenger seat

(i.e., an infant or child in a child seat, a child outside of

a child seat, or an adult).

• Possible use of seat belt tension sensors and/or

occupant position sensors to augment information

provided by above sensors.

Crash sensors Vehicles with multistage air bags have crash

sensing systems that have been refined to better

discriminate among crash severity levels. These

sensors are located in the passenger compartment;

some are augmented by front (crush zone) sensors.

Crash sensing systems with a greater ability to

differentiate levels of crash severity as well as types of

crashes. Use of front (crush zone) sensors expected to

increase.

Control module Vehicles with multistage air bags have more

complex computational systems designed to make

timely decisions about the appropriate level of air

bag deployment based on input from crash sensors

and, as applicable, occupant sensors.

Computational systems of increased complexity that will

be able to process more inputs from crash sensors and

occupant classification sensors and make timely

decisions regarding the appropriate level of air bag

deployment.

Multistage

inflators

Vehicles with multistage air bags have inflators with

2 or 3 levels of deployment. Deployment decisions

are based on input from crash sensors and, as

applicable, occupant classification sensors.

Inflators with 2 or more levels of deployment. Deployment

decisions will be based on input from crash sensors and

occupant classification sensors.

Air bags Newer vehicles have air bags with improved

designs aimed at reducing the aggressivity of the

deploying bag. Improvements have included moving

the air bag module further away from the occupant,

use of tethers within the bag, and changes in bag

folding, shapes, and venting.

Further improvements may include increased use of

innovative bag designs as well as new designs aimed at

enhancing the ability of the deploying air bag to adapt to

characteristics of the occupant.

Source: GAO analysis of information provided by vehicle manufacturers.

Advanced air bag systems installed in future vehicles will be much more

sophisticated than the conventional air bag systems in today’s vehicles,

because they will be capable of tailoring air bag deployment to

characteristics of the front seat occupants as well as crash severity.

Conventional frontal air bag systems deploy the air bags with a single level

of inflation output for all crashes that exceed a predetermined severity

threshold. These systems generally consist of separate components

designed to work together: crash sensors, a control module, and a driver

and passenger inflator and air bag. (See fig. 2.) The crash sensors and

control module are typically located in one unit within the passenger

compartment; the unit is often mounted within the floor between the

driver and the passenger. The crash sensors detect the occurrence and

severity of crashes and provide this input to the control module. The

Components of

Conventional and

Advanced Air Bag Systems
Page 9 GAO-01-596 Vehicle Safety

control module evaluates inputs from the sensors. If the control module

determines that a crash has occurred that exceeds the severity threshold,

it then sends a triggering signal to the inflators to deploy the air bags. The

inflators and air bags are packaged together in air bag modules, which are

located in the steering wheel on the driver side and in the instrument panel

on the passenger side. Upon receiving a triggering signal from the control

module, inflators generate or release gases that rapidly fill the air bags,

generally within 1/20 of a second after impact. The purpose of the inflated

air bags is to provide protective cushioning between the occupants and the

steering wheel, instrument panel, and windshield. However, the “singlestage” inflators in most vehicles today, in some cases, provide more

inflation power than necessary because they fill the air bags with one level

of output when deployed, regardless of the types of occupants requiring

protection or the degree of severity of the crash.

Figure 2: Comparison of Conventional and Advanced Frontal Air Bag Systems

Source: GAO analysis of information provided by vehicle manufacturers and literature on air bag

technologies.

Future frontal air bag systems designed to meet the performance

requirements of NHTSA’s advanced air bag rule will have additional
Page 10 GAO-01-596 Vehicle Safety

features that will allow the deployment of the air bags to adapt to

characteristics of the front seat occupants as well as different crash

situations. Auto manufacturers anticipate that two new components will

be needed to meet the rule’s requirements: occupant classification sensors

and multistage inflators. Occupant classification sensors will provide an

additional input to the control module to detect different types of

occupants and whether or not they are belted. For example,

manufacturers anticipate installing sensors that will be able to identify

whether the front passenger seat is occupied by an infant in a rear-facing

child seat, a child, or an adult. Multistage inflators, which will replace

single-stage inflators, will provide varying levels of inflation output that

can be tailored to characteristics of the driver and front seat passenger as

well as different crash scenarios. Deployment options could include no

deployment, low-level output, and high-level output, as well as additional

levels of deployment between the low- and high-output stages. While the

occupant classification sensors and multistage inflators are the key new

features of the advanced air bag systems envisioned by auto

manufacturers, other components will also be improved. For example,

manufacturers anticipate that these systems will include crash sensors

that can more precisely discriminate among different types of crashes

(such as a crash into a rigid concrete wall versus a crash with another

car), control modules that can process the additional inputs provided by

crash and occupant sensors and make more accurate and timely

deployment decisions, and air bag designs that will allow the bag to deploy

less aggressively.

These advanced air bag systems will be designed to reduce the likelihood

of the types of fatalities previously caused by air bag deployments. For

example, such systems would deactivate the passenger air bag or deploy it

at a low level if the passenger seat is occupied by an infant or small child.10

These systems may also adjust air bag deployment if the driver or

passenger is a small adult.

 10NHTSA has stressed that children are safest in the back seat and that this will continue to

be the case even in vehicles that have advanced air bag systems.
Page 11 GAO-01-596 Vehicle Safety

Some vehicles on the U.S. market today have frontal air bag systems with

multistage inflators and some other advanced features, such as seat belt

usage sensors and improved air bag designs.11 However, no vehicles

currently on the market have air bag systems with all the features

manufacturers believe are needed to fulfill the requirements of the

advanced air bag rule. In particular, no vehicles currently have frontal air

bag systems with occupant classification sensors that can distinguish

among child seats, children, or adults. Manufacturers are not required to

produce vehicles that can meet the requirements of the advanced air bag

rule until the production year starting in September 2003 (approximately

model year 2004).

Frontal air bag systems with multistage inflators started appearing on the

market in some model year 1999 and 2000 vehicles and became more

widely available in model year 2001 vehicles. While three of the eight

manufacturers we talked to installed multistage air bag systems in some or

all of their model year 1999 vehicles, seven of the manufacturers installed

this technology in some or all of their model year 2001 vehicles. Four of

these seven manufacturers—BMW, DaimlerChrysler, Ford, and Honda—

installed multistage air bag systems in at least one-quarter of their model

year 2001 fleets.12 While most of the multistage air bag systems installed in

these model year 2001 vehicles have two stages of inflation, some have

three stages. Manufacturers are planning to further increase the number of

vehicles with multistage air bag systems in their model year 2002 fleets.

(See app. III for more detailed information on the availability and features

of multistage frontal air bag systems in U.S. market vehicles.)

Most of the multistage air bag systems installed in vehicles on the market

today have one or more types of sensors that provide information about

 11Many vehicles on the market today also have newer seat belt features that improve the

performance of the occupant restraint system in protecting occupants. For example, seat

belt pretensioners retract a limited amount of webbing to help minimize the forward

movement of the occupant during a crash. Also, energy management features prevent belts

from concentrating too much energy on the occupant’s chest during a severe crash. These

include “load limiters” built into the shoulder belt retractor and/or “tear stitching” in the

webbing that causes the seat belt to extend gradually.

12BMW, DaimlerChrysler (Mercedes-Benz), and Honda introduced multistage air bag

systems in their model year 1999 fleets; Ford and General Motors introduced them in their

model year 2000 fleets; and Nissan and Toyota introduced them in their model year 2001

fleets. The availability of multistage air bag systems in model year 2001 vehicles, as a

percentage of each company’s fleet, was: BMW-100 percent, DaimlerChrysler-27 percent,

Ford-31 percent, General Motors-10 percent, Honda-74 percent, Nissan-19 percent, and

Toyota-1 percent.

Some Advanced Air Bag

Technologies Are

Currently Available
Page 12 GAO-01-596 Vehicle Safety

the front seat occupants, such as the presence of an occupant in the

passenger seat, driver seat position, and driver and passenger seat belt

use. In air bag systems with these occupant sensors installed, the control

module utilizes input from these sensors, in addition to input from the

crash sensors, in making deployment decisions.

• Three manufacturers—BMW, DaimlerChrysler (Mercedes-Benz), and

Ford—have offered some model year 2001 vehicles equipped with weightbased occupant presence sensors on the passenger side. In these vehicles,

the control module deactivates the passenger air bag if the sensor detects

that the passenger seat is unoccupied. The main purpose of these sensors

is to prevent unnecessary deployment of the passenger air bag and save on

repair costs. The sensors are not capable of identifying what type of

occupant is in the passenger seat.13

• One manufacturer—Ford—has offered model year 2001 vehicles equipped

with sensors that detect whether the driver’s seat is positioned forward or

rearward on the seat track. When the sensor detects that the seat is

positioned forward, indicating that the driver is seated close to the air bag

module, the control module deactivates the high-output stage of the

driver’s air bag.

• Four manufacturers—BMW, DaimlerChrysler (Mercedes-Benz), Ford, and

Honda—have offered some model year 2001 vehicles that contain, as part

of their multistage air bag systems, sensors that detect whether the

occupants are wearing seat belts. The control module deploys the air bags

at a higher crash severity threshold if the occupant is belted and a lower

threshold if the occupant is unbelted.14

In addition to installing the new air bag technologies described above,

manufacturers have also made improvements to crash sensors, control

modules, and air bags. In currently available multistage air bag systems,

the level of air bag deployment in a crash is based on the level of crash

severity, although the occupant sensors described above also affect

deployment decisions in some vehicles. The crash sensors in these

systems have been refined to better discriminate crash severity levels.

 13However, the occupant presence sensing system in Mercedes-Benz vehicles does have the

capability of detecting the presence of a compatible child seat in the front passenger seat,

through a tag in the bottom of the child seat. The control module deactivates the passenger

air bag when the tag is detected.

14Although Volkswagen has not produced any vehicles with multistage air bag systems,

some of the company’s model year 2001 vehicles have these types of belt use sensors

installed.
Page 13 GAO-01-596 Vehicle Safety

These crash sensors are generally arranged in one of two ways. In the first

type of arrangement, which is typically used in conventional air bag

systems, a “single-point” electronic crash sensor is located within the

control module in the passenger compartment. In the second type of

arrangement, called a “multipoint” electronic crash sensing system, one

sensor is located within the control module and one or more sensors are

located in the front (crush zone) of the vehicle.

In all of the multistage air bag systems installed in vehicles on the market

today, the control modules contain more complex computational systems

designed to make timely decisions about the appropriate level of air bag

deployment. In multistage air bag systems that include occupant sensors

and/or multipoint crash sensing systems, the control modules must

process the additional inputs provided by these sensors in making

deployment decisions.

Manufacturers have made a variety of improvements in their air bag

designs aimed at reducing the aggressivity of the deploying air bag and,

therefore, the risk of injury caused by deployment. One major area of

improvement has been to change the location of the air bag module or the

size, shape, and folding of the bag to increase the distance between the

occupant and the deploying air bag. For example, on the driver side,

manufacturers now often recess the air bag into the steering wheel and

employ a fold and shape that allows the bag to deploy laterally rather than

rearward toward the driver. Some passenger air bags in use today contain

a device that directs the initial inflation of the bag away from the occupant

if he or she is in close proximity to the bag at the time of deployment.

Other improvements in bag design that are used in some vehicles include

vents that can make the bag deploy more softly if it is obstructed by the

occupant during deployment and the use of tethers within the bag to

reduce extension when deployed. (For further information on advanced

technologies currently installed in vehicles, see app. IV.)

Vehicle manufacturers, along with companies that supply them with air

bag systems, are working now on developing frontal air bag systems that

are intended to meet the requirements in the advanced air bag rule and be

ready to be installed in model year 2004 vehicles, as required. The

advanced air bag systems envisioned by manufacturers for meeting the

rule’s requirements include new technologies that have not previously

been installed in vehicles as well as significant improvements in existing

technologies.

Significant Improvements

Are Under Development
Page 14 GAO-01-596 Vehicle Safety

The key new technologies that manufacturers anticipate will be needed to

comply with the advanced air bag rule are occupant classification sensors

that can identify whether the passenger seat is occupied by an infant in a

child seat, a small child in or out of a child seat, or a small adult. Air bag

suppliers have been working on the development of a number of such

sensor technologies, and manufacturers are currently considering these

technologies. The primary technologies under consideration are weightbased sensors and pattern-based sensors, which would be installed within

or under the passenger seat. Weight-based sensors attempt to classify the

occupant through various means of determining the amount of force or

pressure applied to the seat. Pattern-based sensors attempt to classify an

occupant using a mat, installed directly under the seat cover, which senses

the occupant’s applied pressure and imprint. Manufacturers are also

considering augmenting some of these technologies with seat belt tension

sensors to identify whether the amount of force applied to the seat is due

in part to the seat belt rather than the occupant’s weight. In addition to

developing new sensors for identifying the type of occupant in the

passenger seat, manufacturers plan to increase the use of driver and

passenger seat belt use sensors and driver seat position sensors. As

described in the previous section, these occupant sensor technologies are

already developed and available in some vehicles.

Manufacturers also plan to continue making improvements in existing

technologies for crash sensors, control modules, inflators, and air bags to

comply with the advanced air bag rule. Manufacturers and suppliers are

working on improving the ability of crash sensing systems to differentiate

levels of crash severity and types of crashes. As part of this effort,

manufacturers plan to increase the use of multipoint crash sensing

systems. Manufacturers and suppliers are also developing more complex

computational systems to be incorporated into control modules, in order

to allow them to process the additional inputs in advanced air bag systems

and to make accurate and timely decisions regarding deployment outputs.

Manufacturers will use multistage inflators that have two or more stages

of inflation output in their advanced air bag systems. Some manufacturers

have already installed inflators with more than two stages of inflation on a

limited basis, but other manufacturers have told us that they do not plan to

use them until occupant classification and control module technologies

are more fully developed. Finally, manufacturers and suppliers continue to

work on improvements in air bag design, such as venting and bag shapes,

in order to enhance the ability of vehicles to comply with the advanced air

bag rule. Further improvements may include increased use of innovative

bag designs as well as new designs that will enhance the ability of the

deploying air bag to adapt to characteristics of the occupant.
Page 15 GAO-01-596 Vehicle Safety

Vehicle manufacturers and air bag suppliers are also researching some

other advanced air bag technologies that are not considered necessary for

complying with the advanced air bag rule but that may be used in the

longer term to enhance the performance of air bag systems.

• Some manufacturers and air bag suppliers are researching “dynamic”

occupant position sensing, which would continuously track the proximity

of the occupant to the air bag. Inputs from these sensors, which would be

installed in the passenger compartment, would be used by the control

module to determine when the occupant is in close proximity to the air

bag and, when this is the case, to deactivate the bag. “Static” sensors that

periodically determine the occupant’s position may be installed on a

limited basis in the near term to augment occupant classification sensors.

Although researchers are examining various technologies for achieving

dynamic occupant position sensing, it is not yet clear whether or when this

technology will become widely used.

• Precrash sensing is another area of technology currently in the research

stage. These sensors would identify the position, speed, and mass of

objects prior to a collision and allow more time for the air bag system to

respond. The feasibility of this concept has not yet been determined;

therefore, it is not yet clear when this technology might become available.

• Some suppliers are researching inflator technologies that may produce

continuous variation in inflation, rather than inflation in discrete stages,

allowing air bag deployment to be more adaptive to inputs from crash and

occupant sensors. These may be introduced by some manufacturers

during the initial 3-year phase-in period for complying with the advanced

air bag rule.

(For further details on anticipated advancements in air bag technologies,

see app. IV.)
Page 16 GAO-01-596 Vehicle Safety

According to representatives of vehicle manufacturers and air bag

suppliers, the primary challenge in meeting the requirements of the

advanced air bag rule is developing occupant classification sensors for the

passenger side that are accurate, durable, and suitable for mass

production before September 2003. The rule requires manufacturers to

install advanced air bag systems that either suppress the air bag if an

infant or child is seated in the passenger seat or deploy it in a “low-risk”

manner that does not cause severe or fatal injury, even if the infant or

child is out of position.15 If the system is designed to suppress the air bag in

the presence of an infant or child, it must deploy if the passenger is a small

adult (defined as a 5th percentile woman). To test whether a sensor

accurately classifies an occupant so the air bag can deploy appropriately,

the rule specifies tests using dummies representing infants, 3-year-old and

6-year-old children, and 5th percentile women. The dummies have fixed

weights, heights, and stature that are easily distinguishable from each

other. However, the rule also requires that some tests be conducted using

child seats, variable seat belt tension, blankets, and with the dummies in

various positions. These added factors make it more difficult for sensors

to distinguish among the different occupants. In addition to the

requirements in the rule, manufacturer and supplier representatives told

us that they are designing occupant classification sensors for additional

“real-world” situations that further challenge the ability of sensors to

perform accurately. Such real-world situations could include variation in

the actual weight of humans, changes in weight detected by sensors as the

occupant moves forward, backward, and side-to-side, or increased weight

from objects held on laps.

Manufacturers generally require that technologies perform accurately over

99 percent of the time before being installed in vehicles. However,

manufacturer representatives told us that technologies that are currently

being developed for occupant classification sensors, such as weight-based

or pattern-based sensors, have not demonstrated the ability to consistently

distinguish among various sizes of occupants. For example, weight-based

sensors in seats have difficulty distinguishing between 6-year-old children

and small adults because a 6-year-old child can appear heavier from

additional weight (such as a booster seat and increased tension from a

 15The rule also allows manufacturers the option of suppressing the air bag if the occupant

moves out of position during a crash, as occurs in precrash braking. However, NHTSA has

not developed performance requirements and test procedures for a system that

dynamically suppresses the air bag. In addition, manufacturer representatives told us that

they are not planning to install such a system before September 2003 because the

technologies needed for this system—dynamic occupant position sensors—are not

sufficiently developed.

Occupant Sensing Is

the Primary Challenge

in Meeting the

Advanced Air Bag

Rule’s Requirements
Page 17 GAO-01-596 Vehicle Safety

tightly cinched seat belt); additionally, small adults can appear lighter

because a portion of the occupant’s weight is borne by the legs resting on

the floor. Pattern-based sensors must first be programmed to recognize

various seating positions. If a child or a small adult sits in a position that

was not previously anticipated and programmed for the sensor, the system

could mistake the child for an adult or vice versa. Incorrect classification

of an occupant could result in the system mistakenly deploying the air bag

in the presence of a child, not deploying in the presence of an adult, or

deploying the air bag with greater or less force than intended.

In addition to performing accurately, occupant classification sensors must

also be durable and capable of being consistently produced and integrated

into vehicles in large quantities. Air bag systems are expected to operate

reliably over the life span of a vehicle, which could be up to 15 years.

However, sensors are susceptible to aging and environmental influences

over that time. For example, the performance of pattern-based sensors

that are installed directly under the seat cover could be affected by

deterioration of the seat cover. Sensor performance is also affected by

variations in the manufacturing process that can affect the construction of

the sensor or how easily it can be integrated into the vehicle. The parts of

a sensor must be precisely constructed because inconsistencies in the

parts can cause the sensor to malfunction. Sensors that are integrated into

a seat are also subject to variations in how the seat is constructed.

According to vehicle manufacturer representatives, companies that

produce vehicle seats will have to significantly redesign seats and

decrease the variation in the production of seats before occupant

classification sensors can consistently function properly.

Vehicle manufacturers are working with the companies that supply air bag

systems to find solutions to these accuracy, durability, and manufacturing

issues. For example, to address the influence of seat belt tension on

weight-based sensors, some manufacturers and suppliers are developing

seat belt tension sensors that would detect when the seat belt is cinched

tightly and causing the occupant to appear heavier. Individual

manufacturers are simultaneously developing multiple occupant

classification technologies with different suppliers to increase the

likelihood of finding a solution by the deadline. Some manufacturers told

us they have also postponed research on occupant position sensors so

they can focus on occupant classification sensors.

According to representatives of some vehicle manufacturers, their goal is

to install occupant classification sensors 1 year before the September 2003

deadline in order to get real-world experience with the performance of the

sensors. However, a number of vehicle manufacturers have expressed
Page 18 GAO-01-596 Vehicle Safety

concerns about their ability to develop occupant classification sensors

that comply with the advanced air bag rule by the deadline—slightly more

than 2 years away. Despite the fact that manufacturers have been working

on technologies for occupant classification sensors for several years, the

development of these technologies has not yet reached the level that a new

technology would normally have reached to be ready for installation

within that time frame. In 1998 and 1999, NHTSA reported that vehicle

manufacturers anticipated having occupant classification sensors installed

in model year 2000 vehicles.16 However, accuracy, durability, and

manufacturing issues were more difficult to overcome than anticipated.

For example, General Motors anticipated installing a pattern-based sensor

in its model year 2000 Cadillac Seville but abandoned this plan in part

because the sensor did not perform accurately under different humidity

and temperature settings, and the production process was so variable that

only 10 percent of the sensors that were produced were suitable for

installation in vehicles. More recently, in March 2001, after 2 years of

work, a company that was to be the primary supplier of a weight-sensing

system for DaimlerChrysler decided to abandoned work on the project

due to technical reasons. As a result, DaimlerChrysler is reevaluating its

options for occupant classification sensors.

NHTSA officials have met with industry representatives to discuss their

efforts to develop advanced air bag systems. According to NHTSA

officials, although vehicle manufacturers have stated that it will be

difficult to develop occupant classification sensors by September 2003,

none of the manufacturers have indicated that they will not be able to

meet the deadline.17

Due to the uncertainty associated with developing occupant classification

sensors, NHTSA plans to stay abreast of manufacturers’ progress by

holding periodic meetings with manufacturers. These meetings may be

informal meetings that occur as NHTSA gathers information about

technologies or more formal meetings for manufacturers to provide an

update on the status of their progress. NHTSA also plans to conduct

research on the feasibility of occupant classification technologies,

including laboratory research on specific occupant classification

 16Advanced Air Bag Technology Assessment, Prepared for NHTSA and the National

Aeronautics and Space Administration by the Jet Propulsion Laboratory, April 1998; Air

Bag Technology in Light Passenger Vehicles, NHTSA, December 16, 1999, Revision 1.

17Should a manufacturer be unable to meet the deadline, the manufacturer may apply to

NHTSA for a temporary exemption from the requirements.
Page 19 GAO-01-596 Vehicle Safety

technologies and monitoring the performance of occupant classification

technologies as they are installed in vehicles.

Other technological challenges described by manufacturers include

designing an air bag that can generate enough power to protect an average

adult male as well as deploy in a manner that does not severely injure a

smaller occupant and developing crash sensors that can distinguish among

the various types of crash tests required in the rule. In addition to the

technological challenges of developing an advanced air bag system,

manufacturers and suppliers are concerned about the accuracy and

repeatability of some of the test procedures in the rule and using humans

rather than dummies to test suppression systems. These concerns were

highlighted in petitions for reconsideration of the rule filed by the

manufacturers. (See app. II for further information on these petitions for

reconsideration and NHTSA’s response.)

NHTSA’s reported expenditures on advanced air bag R&D increased from

about $6.3 million in fiscal year 1998 to nearly $7.0 million in fiscal year

2000. (See table 2.) According to NHTSA officials, these expenditures were

primarily for activities related to the development of the advanced air bag

rule, such as investigations of crashes involving an air bag-related injury or

fatality, evaluations of the performance and characteristics of air bag

systems, and studies to determine how people are injured or killed by air

bags. NHTSA officials estimate that expenditures on advanced air bag

R&D will increase to $7.2 million in fiscal year 2001. According to NHTSA

officials, future expenditures will focus on monitoring the performance of

advanced air bags and continuing the R&D of specific technologies.

NHTSA’s planned activities include analyzing the protection provided by

advanced air bags in real-world crashes, conducting crash tests—including

tests at various speeds and angles with belted and unbelted crash

dummies—to evaluate the performance of advanced air bags, and

researching advanced air bag technologies that are anticipated to be ready

for installation in vehicles in the next 3 to 5 years. NHTSA plans to

conduct some of this research through cooperative agreements with air

bag suppliers.

Federal and Industry

Expenditures on

Advanced Air Bag

Research and

Development Have

Increased Since 1998
Page 20 GAO-01-596 Vehicle Safety

Table 2: NHTSA Expenditures on R&D for Advanced Air Bag Technologies, Fiscal

Years 1998-2001

Dollars in thousands

Category 1998 1999 2000 2001(est.)

Special crash investigations $1,331 $1,553 $1,553 $1,553

Air bag systems 1,850 2,431 2,431 2,480

Biomechanics (crash dummies) 3,150 3,000 3,000 3,200

Total $6,331 $6,984 $6,984 $7,233

Note: These expenditures do not include other NHTSA expenditures that indirectly benefit air bag

R&D, such as the New Car Assessment Program and compliance testing.

Source: NHTSA.

Vehicle manufacturers did not provide information on their individual

expenditures for advanced air bag R&D because they consider this

information confidential. Instead, an industry association—the Alliance of

Automobile Manufacturers—coordinated with manufacturers to provide

aggregated information on the extent to which expenditures have changed

and are anticipated to change compared to calendar year 1998. Four

manufacturers—Ford, General Motors, Nissan, and Toyota—provided

information on expenditures for resources related to one or more of the

following categories: staffing (including expenditures to support supplier

staffing); technology development and testing; prototype parts;

engineering resources; in-house testing and data analysis, analytical

performance assessment (computer modeling), physical test properties

and test costs; and implementation and integration of technologies into

vehicles. According to the Alliance, these expenditures generally total

between $20 million and $30 million per vehicle “platform” (a group of

vehicles that utilize the same basic design).18 The aggregated information

from the four manufacturers shows that their expenditures increased by

about 275 percent from 1998 to 2000 and are anticipated to increase

overall by nearly 375 percent from 1998 through 2003. (See fig. 3.)

According to the Alliance, the estimated increase from 1998 through 2003

is due to the cost of designing and installing advanced air bag systems for

an increasing number of vehicle platforms to meet the phase-in

requirements in the advanced air bag rule. These expenditures are

estimated to decrease after advanced air bag systems have been installed

in vehicles.

 18A single vehicle platform could encompass one or several models of vehicles. According

to the Alliance and vehicle manufacturers, the 8 vehicle manufacturers included in our

review have 88 vehicle platforms.
Page 21 GAO-01-596 Vehicle Safety

Figure 3: Percentage Change in Four Vehicle Manufacturers’ Advanced Air Bag

R&D Expenditures, 1999 Through 2004

Note: 1998 is the baseline year. The Alliance adjusted each company’s expenditures by its current

market share and averaged the sum of the manufacturers’ adjusted expenditures for each year.

Source: Alliance of Automobile Manufacturers.

We provided a draft of this report to the Department of Transportation for

its review and comment. The Department did not provide an overall

assessment of our draft report. Rather, Department representatives,

including the Director of NHTSA’s Office of Vehicle Safety Research,

provided one technical comment through e-mail. Specifically, the Director

suggested that several manufacturers may have the necessary technologies

for occupant classification sensors that can distinguish among various

sizes of occupants, even though they may not have installed them in

vehicles on a large scale. We verified with auto manufacturers that they

have not installed occupant classification sensors that can distinguish

among various sizes of occupants and are still developing such sensors for

Agency and Industry

Comments and Our

Evaluation
Page 22 GAO-01-596 Vehicle Safety

frontal air bag systems that are intended to meet the requirements of the

advanced air bag rule.

We provided portions of our draft report to vehicle manufacturers and air

bag suppliers for review to verify the accuracy of our descriptions of

advanced air bag technologies and challenges in meeting the requirements

of the advanced air bag rule. The manufacturers and suppliers generally

agreed with our draft report and offered several technical corrections,

which we incorporated as appropriate.

We are sending copies of this report to congressional committees and

subcommittees responsible for transportation safety issues; the Secretary

of Transportation; the Executive Director, National Highway Traffic Safety

Administration; the Director, Office of Management and Budget; and other

interested parties. We will make copies available to others upon request

and on GAO’s home page at http://www.gao.gov.

If you or your staff have any questions about this report, please contact me

at (202) 512-2834. Key contributors to this report were Judy GuilliamsTapia, Bert Japikse, James Ratzenberger, Phyllis Scheinberg, and Sara

Vermillion.

John H. Anderson, Jr.

Managing Director, Physical Infrastructure Issues
Appendix I: Scope and Methodology

Page 23 GAO-01-596 Vehicle Safety

To determine the current availability of and planned improvements to

advanced air bag technologies, we collected and analyzed information

from eight vehicle manufacturers (BMW, DaimlerChrysler, Ford, General

Motors, Honda, Nissan, Toyota, and Volkswagen) and the five companies

that are the primary suppliers of air bag systems in the United States

(Autoliv, Breed, Delphi, Takata, and TRW). According to the Alliance for

Automobile Manufacturers, the combined sales for the eight

manufacturers account for over 90 percent of vehicles sold in the United

States. We did not independently verify the information we received from

manufacturers and suppliers. We reviewed literature on automotive

technology for descriptions of the technologies used in advanced air bag

development. We also met with officials from NHTSA, representatives

from the Insurance Institute for Highway Safety, the National

Transportation Safety Board, university researchers, and consumer

groups.

To identify the challenges, if any, that the industry faces in complying with

the advanced air bag rule, we reviewed the requirements of the rule and

discussed these requirements with representatives of vehicle

manufacturers and companies that supply air bags. We also reviewed

comments on the rule submitted by manufacturers and suppliers.

To identify the changes in federal expenditures on advanced air bag R&D,

we collected data on NHTSA’s expenditures for fiscal years 1998 through

2001 and analyzed the changes in the individual categories of

expenditures. Vehicle manufacturers did not provide information on their

individual expenditures for advanced air bag R&D because they consider

this information confidential. Therefore, to identify the changes in industry

expenditures on advanced air bag R&D, we collected aggregated

information from an industry association on the extent to which four

manufacturers’ expenditures have changed since 1998. We did not

independently verify this aggregated information.

We conducted our work from July 2000 through May 2001 in accordance

with generally accepted government auditing standards.

Appendix I: Scope and Methodology
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 24 GAO-01-596 Vehicle Safety

The advanced air bag rule requires that future air bags be designed to

create less risk of serious injury from air bags—particularly for small

women and young children—and to improve frontal crash protection for

all occupants. To achieve these goals, the rule includes requirements for

additional test procedures using different sizes of dummies than were

included in previous requirements. These new requirements will be phased

in during two stages. During the first stage phase-in—from September 1,

2003, to August 31, 2006—an increasing number of each manufacturer’s

vehicles must be certified each year as meeting the requirements in the

advanced air bag rule. During the second stage phase-in—from September

1, 2007, to August 31, 2010—the speed for one of the tests (the belted test

for the 50th percentile adult male dummy) will be increased from 30 to 35

miles per hour (mph) and, similar to the first phase-in period, an

increasing number of each manufacturer’s vehicles must be certified each

year.

In comments to the supplemental notice of proposed rulemaking on

advanced air bags, there was a difference of opinion on whether the

maximum speed for the unbelted rigid barrier crash test should be set at

25 or 30 mph. In the final rule, NHTSA set the maximum speed at 25 mph

on an interim basis while the agency continues to investigate whether the

higher speed is more appropriate. After the rule was issued in May 2000,

consumer safety groups, vehicle manufacturers, and air bag suppliers filed

petitions for NHTSA to consider changing certain provisions in the rule.

NHTSA plans to respond to these petitions in July 2001.

To minimize risk to infants and children on the passenger side, the rule

includes provisions for the air bag to be suppressed or deployed in a “lowrisk” manner that is much less likely to cause serious or fatal injury. (See

fig. 4.) For newborn infants in car beds, the rule requires that the air bag

be suppressed. For 1-year-old infants in child seats, 3-year-old children,

and 6-year-old children, manufacturers are allowed to install systems

designed for suppression or low-risk deployment. Manufacturers may

choose different strategies for different occupants. For example, a

manufacturer could design an air bag system that would suppress the air

bag for infants and deploy the bag in a low-risk manner for 3- and 6-yearold children.

Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Selected

Requirements in the

Advanced Air Bag

Rule
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 25 GAO-01-596 Vehicle Safety

Figure 4: Test Options in the Advanced Air Bag Rule to Meet Suppression and LowRisk Deployment Requirements for Smaller Occupants

a

This option allows manufacturers to suppress the air bag if the occupant (3-year-old or 6-year-old on

the passenger side or small female on the driver side) moves “out of position,” or close to the air bag

module during a crash, as occurs in precrash braking. NHTSA has not adopted performance

requirements and test procedures for such a system that would “dynamically” suppress the air bag,

but may do so at a later date. Several manufacturers told us that they are not planning to install such

a system before September 2003 because the technologies needed for this system—dynamic

occupant position sensors—are not sufficiently developed.

Source: NHTSA.

To test for suppression on the passenger side, the dummies are placed in

their appropriate child seats that are, in turn, placed on the passenger

seat.1

 These tests may be conducted under various scenarios: using any of

several models of safety seats; with the passenger seat in the forward,

middle, or rear position; unbelted or belted with up to 30 pounds of

tension on the belt; with any handles and sunshields on infant safety seats

in fully open and fully closed positions; or with a towel or blanket on the

infant safety seats. For the 3- and 6-year-old dummies, tests will also be

conducted with the dummies unbelted and in various positions, such as

 1

Newborn infant dummies are placed in car beds. One-year-old dummies are placed in rearfacing or forward-facing child safety seats. Three-year-old dummies are placed in forwardfacing child seats or booster seats. Six-year-old dummies are placed in booster seats.
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 26 GAO-01-596 Vehicle Safety

sitting back or sitting on the front edge of the seat.2 The rule requires that

the car have a “telltale” light that, after the dummy is in place, indicates

whether the air bag is suppressed or activated. Following each

suppression test with an infant or child, a dummy representing a small (5th

percentile) adult female will be placed in the passenger seat to ensure that

the air bag is not suppressed for small adults.

To test for low-risk deployment on the passenger side, a 1-year-old dummy

is placed in one of several models of rear- or forward-facing child seats on

the passenger seat in the forward position on the seat track. The seat belt

may be cinched with up to 30 pounds of tension. For the 3- and 6-year-old

dummies, the unbelted dummy is placed “out of position” with their head

or chest on the air bag module to simulate the situation where an unbelted

child is close to the instrument panel due to sudden braking immediately

before a crash. After the dummy (infant or child) is in place, the air bag is

deployed. The amount of “injury” that occurs to the head and neck of the

dummies (and the chest of the 3- and 6-year-old child dummies) must be

below criteria specified in the rule.

To minimize risk to small drivers, the rule includes provisions to deploy

the air bag in a low-risk manner, similar to the low-risk deployment tests

for 3- and 6-year-old children.3

 The tests are conducted by placing the 5th

percentile adult female dummy out of position, with the chin on the

steering wheel rim or on the air bag module. The air bag is then deployed

and the resulting “injury” to the head, neck, chest, and legs is measured.

NHTSA has determined that, when all of the combinations of the various

testing scenarios are considered, there are 129 tests for suppression and

low-risk deployment: 95 suppression tests for infants in a car bed or child

seat, 28 suppression tests for 3- and 6-year-old children, 4 low-risk

 2

Crash dummies do not sufficiently represent the human physiology, so the rule allows the

use of appropriately sized humans to test the performance of the technologies in static

suppression tests. The University of Michigan Transportation Research Institute is

developing dummies that more accurately represent the human shape.

3

The rule also allows manufacturers the option of suppressing the air bag if the occupant

moves out of position during a crash, as occurs in precrash braking. However, NHTSA has

not developed performance requirements and test procedures for a system that

dynamically suppresses the air bag. In addition, manufacturer representatives told us that

they are not planning to install such a system before September 2003 because the

technologies needed for this system—dynamic occupant position sensors—are not

sufficiently developed.
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 27 GAO-01-596 Vehicle Safety

deployment tests for 3- and 6-year-old children, and 2 low-risk deployment

tests for 5th percentile female drivers.

To improve protection in frontal crashes for occupants of different sizes,

the rule includes seven tests that involve crashing vehicles into barriers at

different speeds and angles and with dummies representing average (50th

percentile) adult males and 5th percentile women, belted and unbelted.

(See fig. 5.) Four of the tests are conducted with dummies that represent

50th percentile adult males and three are conducted with dummies that

represent 5th percentile adult females. After the crash test, the resulting

injury to the head, neck, chest, and legs of the dummies must not exceed

the limits specified in the rule. The offset deformable barrier test was

included in the requirements to ensure that manufacturers upgrade their

crash sensors as necessary to prevent late air bag deployments in crashes

that are less abrupt than those into rigid barriers. NHTSA did not include a

requirement for an unbelted crash test at an oblique angle using a 5th

percentile female dummy because the agency determined that the

requirement for this type of crash using a 50th percentile male dummy

would result in an air bag that is sufficient to protect smaller occupants as

well.
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 28 GAO-01-596 Vehicle Safety

Figure 5: Tests Required in the Advanced Air Bag Rule to Improve Protection for Occupants of Different Sizes

a

Maximum speed will increase to 35 mph after September 1, 2007.

Source: NHTSA.

The rule will be phased in during two stages. The first stage phase-in—

from September 1, 2003, to August 31, 2006—requires an increasing

number of vehicles to be certified as passing all of the above tests each

year. (See fig. 6.) During the second stage phase-in—from September 1,

2007, to August 31, 2010—the speed for the belted test for the 50th

percentile adult male dummy will be increased from 30 to 35 mph. As with

the earlier requirements, an increasing percentage of vehicles must comply

with the new test speed each year.
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 29 GAO-01-596 Vehicle Safety

Figure 6: Timeline for Phase-in of Requirements in the Advanced Air Bag Rule

Source: GAO analysis of information from NHTSA.

In the comments to the supplementary notice of proposed rulemaking for

the advanced air bag rule, there was a significant difference of opinion on

whether the top speed for the unbelted rigid barrier crash test should be

set at 30 mph or 25 mph.4 Comments from those who favored setting the

maximum test speed at 30 mph—safety groups such as Public Citizen,

 4

While the speed of a rigid barrier crash test at 30 mph is 20 percent higher than a test at 25

mph, it represents a 44 percent increase in crash energy.

Comments on the

Maximum Speed for

the Unbelted Rigid

Barrier Test
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 30 GAO-01-596 Vehicle Safety

Center for Auto Safety, Consumers Union, and Parents for Safer Air

Bags—included:

• half of all fatalities in frontal crashes involve a change in velocity greater

than 30 mph, so a maximum test speed of 30 mph represents significantly

more potentially fatal crashes than a test speed of 25 mph;

• in crash tests conducted by NHTSA, almost all vehicles with redesigned air

bags passed the 30 mph unbelted rigid barrier test with the 50th percentile

male dummy, so air bags would not have to be more aggressive (and

potentially more risky to small occupants) to meet a 30 mph test;

• lowering the test speed to 25 mph would not offer improved protection, as

required in the Transportation Equity Act for the 21st Century;

• advanced technologies can be used to enable all vehicles to meet

requirements for high speed protection and risk reduction; and

• a 25 mph test speed would not encourage the use of advanced

technologies.

Comments from proponents of a 25 mph maximum test speed—such as

vehicle manufacturers, air bag suppliers, the Insurance Institute for

Highway Safety, and the National Transportation Safety Board—included:

• redesigned air bags work well and there has been no loss in protection;

• a 25 mph test speed allows flexibility to design air bags for all occupants;

• a return to a 30 mph test would require a return to overly powerful air

bags;

• there are significant technological challenges in meeting a 30 mph

requirement for both the 50th percentile adult male dummy and the 5th

percentile adult female dummy; and

• advanced technologies are not currently available that address problems

posed by air bags designed to a 30 mph test.

NHTSA concluded that, given the uncertainty associated with

simultaneously achieving improved protection for occupants of all sizes

without compromising efforts to reduce the risks of injury to smaller

occupants, a conservative approach should be taken. Consequently,

NHTSA set the maximum speed for the unbelted rigid barrier test at 25

mph. However, the agency issued that part of the rule as an interim final

rule and announced that it would issue a final rule after it monitors the

performance of advanced air bags and determines whether increasing the

maximum test speed to 30 mph would offer any advantages over a test

speed of 25 mph. To monitor the performance of advanced air bags,

NHTSA plans to, among other things, evaluate real-world crash data,

perform compliance testing and publish an annual report on the extent to
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 31 GAO-01-596 Vehicle Safety

which advanced air bags comply with requirements, conduct crash tests,

and conduct research on specific advanced air bag technologies.

After the final rule was issued in May 2000, consumer safety groups,

vehicle manufacturers, and air bag suppliers submitted petitions to NHTSA

for the agency to reconsider certain aspects of the rule. Consumer safety

groups—Center for Auto Safety, Consumer Federation of America, Parents

for Safer Air Bags, and Public Citizen—jointly filed a petition. The petition

states that separate phase-in schedules for cars and sport utility vehicles

are feasible because some cars can already meet a 30 mph unbelted rigid

barrier crash test, but sport utility vehicles have more difficulty in

complying with this test due to their stiffer frame, which produces a

harder crash pulse and requires a more aggressive air bag than passenger

cars. Specifically, the petition requests NHTSA to require the industry to

meet a 30 mph unbelted rigid barrier test for passenger cars and a 25 mph

test for sport utility vehicles, to be increased to 30 mph at a later date. The

petition also requests NHTSA to: (1) add requirements for tests to simulate

lower-speed, softer crashes in which the air bag deploys late and strikes an

occupant who has moved forward before the air bag deploys, (2) require

manufacturers to meet a 35 mph belted barrier test with the 5th percentile

female dummy as well as the 50th percentile male dummy, and (3) require

that manufacturers conduct all barrier tests in both the perpendicular and

oblique modes, including tests using the 5th percentile female dummies.

Petitions from some vehicle manufacturers and air bag suppliers state that

the directions for some tests in the rule, particularly those related to the

positioning of dummies in suppression and low-risk deployment tests,

need to be clarified. For example, some petitioners claimed that the

procedure for positioning the child dummies for the low-risk deployment

test do not always result in the dummies being against the air bag module,

as intended. Other issues raised in petitions from manufacturers include:

(1) limiting the amount of time required to collect data on the dummies’

injuries during a low-risk deployment test in order to minimize inclusion of

injury from interior components other than the air bag, (2) requesting that

a generic child restraint test device be developed so that humans will not

have to be used to test air bag suppression systems, and (3) reducing the

upper limit on the amount of tension that can be applied to a seat belt.

According to NHTSA officials, NHTSA is drafting a final response to these

petitions and plans to issue the response in July 2001. Some consumer

safety groups and vehicle manufacturers have told us that they are

concerned about the timeliness of NHTSA’s response to the petitions.

Some manufacturers have raised concerns that the issues with the

compliance test procedures may not be resolved in time for them to

Petitions for

Reconsideration
Appendix II: Selected Aspects and Status of

the Advanced Air Bag Rule

Page 32 GAO-01-596 Vehicle Safety

finalize their advanced air bag system designs and perform the required

testing to certify that the vehicles meet the requirements in the advanced

air bag rule.
Appendix III: Multistage Frontal Air Bag

Systems in Model Year 2001 Vehicles and

Model Year 2002 Vehicles in Production as of

April 1, 2001

Page 33 GAO-01-596 Vehicle Safety

Stages of inflation

Types of occupant sensors that affect

air bag deployment

Manufacturer/

make/model

year/vehicle line

Percentage

of U.S.

fleeta Driver Passenger

Type of crash

severity sensorb

Occupant

presence

sensor on

passenger

sidec

Seat

position

sensor on

driver

sided

Belt use

sensor on

driver and

passenger

sidese

BMW

All 2001 vehicles 100 2 2 Single-point electronic ✔ ✔

DaimlerChrysler

Chrysler/Dodge/

Jeep

2001 Sebring/

Stratus Sedan

5 3 3 Single-point electronic

2001 Sebring

Convertible

2 2 2 Single-point electronic

2001 Caravan/

Voyager/Town

and Country

Minivans

16 3 3 Single-point electronic

2002 Jeep Liberty 7 3 3 Multipoint electronic

Mercedes-Benz

2001 C-class 1 2 2 Single-point electronic ✔f✔

2001 S-class 1 1 2 Single-point electronic ✔ f ✔

2001 CL-class <1 1 2 Single-point electronic ✔ f ✔

2001 ML-class 2 2 2 Single-point electronic ✔ f ✔

Ford Motor

Company

Ford/Mercury/

Lincoln

2001

Taurus/Sable

12 2 2 Multipoint electronic ✔ ✔

2001 Crown

Victoria/Grand

Marquis

6 2 2 Multipoint electronic

✔ ✔

2001 Town Car 2 2 2 Multipoint electronic ✔ ✔

2001 Windstar 5 2 2 Multipoint electronic ✔g✔ ✔

Volvo

Appendix III: Multistage Frontal Air Bag

Systems in Model Year 2001 Vehicles and

Model Year 2002 Vehicles in Production as of

April 1, 2001
Appendix III: Multistage Frontal Air Bag

Systems in Model Year 2001 Vehicles and

Model Year 2002 Vehicles in Production as of

April 1, 2001

Page 34 GAO-01-596 Vehicle Safety

Stages of inflation

Types of occupant sensors that affect

air bag deployment

Manufacturer/

make/model

year/vehicle line

Percentage

of U.S.

fleeta

Driver Passenger

Type of crash

severity sensorb

Occupant

presence

sensor on

passenger

sidec

Seat

position

sensor on

driver

sided

Belt use

sensor on

driver and

passenger

sidese

2001 S40 1 2 2 Single-point electronic ✔

2001 S60 <1 2 2 Single-point electronic ✔

2001 S80 1 2 2 Single-point electronic ✔

2001 V40 1 2 2 Single-point electronic ✔

2001 V70 1 2 2 Single-point electronic ✔

2001 Cross

Country

<1 2 2 Single-point electronic ✔

Jaguar

2001 XK Coupe

and Convertible

2 2 2 Single-point electronic ✔ ✔✔

General Motors

2001 Chevrolet

Impala

4 2 2 Multipoint electronic

2001 Chevrolet

Monte Carlo

1 2 2 Multipoint electronic

2001 Buick

Lesabre

3 2 2 Multipoint electronic

2001 Oldsmobile

Aurora

1 2 2 Multipoint electronic

2001 Pontiac

Bonneville

1 2 2 Multipoint electronic

2002 Cadillac

Seville

2 2 2 Multipoint electronic

2002 Buick

Rendezvous

1 2 2 Multipoint electronic

2002 Chevrolet

Trail Blazer

2 2 2 Multipoint electronic

2002 GMC Envoy <1 2 2 Multipoint electronic

2002 Oldsmobile

Bravada

<1 2 2 Multipoint electronic

Honda

Honda

2001 Accord 32 2 2 Single-point electronic ✔

2001 Civic 28 2 2 Multipoint electronic

with mechanical front

sensors

✔
Appendix III: Multistage Frontal Air Bag

Systems in Model Year 2001 Vehicles and

Model Year 2002 Vehicles in Production as of

April 1, 2001

Page 35 GAO-01-596 Vehicle Safety

Stages of inflation

Types of occupant sensors that affect

air bag deployment

Manufacturer/

make/model

year/vehicle line

Percentage

of U.S.

fleeta

Driver Passenger

Type of crash

severity sensorb

Occupant

presence

sensor on

passenger

sidec

Seat

position

sensor on

driver

sided

Belt use

sensor on

driver and

passenger

sidese

Acura

2001 CL 5 1 2 Single-point electronic ✔

2001 MDX 3 1 2 Single-point electronic ✔

2001 RL 1 1 2 Single-point electronic ✔

2001 TL 5 1 2 Single-point electronic ✔

2002 RL N/A 1 2 Single-point electronic ✔

2002 TL N/A 2 2 Single-point electronic ✔

Nissan

2001 Maxima/

Infiniti I30

19 2 2 Multipoint electronic

2002 Q45 N/A 2 2 Multipoint electronic

Toyota

2001 LS430 1 1 2 Multipoint electronic

Legend:

N/A = not available

Note: Table includes U.S. market vehicles only. The checkmarks in the columns for occupant

sensors indicate that these sensors have been installed on the corresponding vehicle.

a

These figures are the approximate percentage that each specified vehicle line represents of the

company’s light vehicles produced during the model year for the U.S. market.

b

Single-point electronic crash sensors are generally located within the control module in the

passenger compartment. In a multipoint crash sensing system, one electronic crash sensor is located

within the control module and one or more electronic or mechanical crash sensors are located in the

front (crush zone) of the vehicle.

c

An occupant presence sensor detects weight on the passenger seat to determine if the seat is

occupied. If the sensor does not detect an occupant over a specified weight, the system deactivates

the passenger air bag.

d

Seat position sensors identify whether the driver’s seat is forward or rearward on the seat track.

When the seat is positioned forward, indicating that the driver is seated close to the steering wheel

and the air bag module, the system deactivates the high output stage of the driver’s air bag.

e

Belt use sensors detect whether the front seat occupants are wearing their seat belts. The system

deploys the air bag at a higher crash velocity threshold if an occupant is buckled and a lower

threshold if an occupant is unbuckled.
Appendix III: Multistage Frontal Air Bag

Systems in Model Year 2001 Vehicles and

Model Year 2002 Vehicles in Production as of

April 1, 2001

Page 36 GAO-01-596 Vehicle Safety

f

The occupant presence sensing system in these vehicles has the capability to detect the presence of

a compatible child seat in the front passenger seat. When the sensor detects the presence of such a

child seat, through a tag in the bottom of the child seat, the system deactivates the passenger air bag.

g

An occupant presence sensing system was incorporated in the front passenger seat of model year

2001 Windstars beginning in May 2001.

Source: GAO analysis of information provided by vehicle manufacturers.
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 37 GAO-01-596 Vehicle Safety

Description: These sensors detect a crash and differentiate levels of crash

severity. They provide this input to the control module, which uses it to

make decisions about whether the air bag should be deployed and, if so,

what level of deployment is appropriate.

Advanced technologies currently available: The crash sensors in vehicles

equipped with multistage frontal air bags have been refined to better

discriminate crash severity levels, so that the appropriate level of air bag

deployment can be determined. Some of these vehicles have a “singlepoint” electronic crash sensor, which is generally located within the

control module in the passenger compartment. Others have “multipoint”

crash sensing systems, in which one sensor is located within the control

module and one or more sensors are located in the front (crush zone) of

the vehicle. In some of these multipoint systems all of the sensors are

electronic while in others the sensor in the control module is electronic

and the sensors in the front of the vehicle are mechanical. Some

manufacturers have placed additional sensors in the front of the vehicle in

order to produce more information on the crash earlier in the crash event,

allowing additional time to determine crash severity and make the

appropriate deployment decision. However, others have not yet installed

up-front crash sensors in their multistage air bag systems, because the

performance of these sensors in “real-world” conditions can be affected by

irrelevant “background noise,” such as extraneous vibrations that occur

during a crash event. (See app. III for information on the types of crash

sensing systems installed in model year 2001 and early model year 2002

vehicles with multistage air bags.)

Anticipated improvements: In order to enhance the ability of their

vehicles to comply with the requirements in the advanced air bag rule,

manufacturers plan to improve the ability of their crash sensing systems to

distinguish among levels of crash severity as well as identify the type of

crash, such as a frontal rigid barrier crash, a pole crash, or an offset

deformable barrier crash. As part of this effort, manufacturers plan to

refine and increase the use of multipoint crash sensing systems.

Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Technologies

Currently Available

and Planned

Enhancements to

Meet Requirements

Crash Sensors
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 38 GAO-01-596 Vehicle Safety

Description: These sensing devices installed in the interior of the vehicle

are intended to identify characteristics of the occupants, such as their

belted status and size. They provide this input to the control module,

which uses it to make decisions about whether the air bag should be

deployed and, if so, what level of deployment is appropriate.

Advanced technologies currently available: Some vehicles currently

equipped with multistage frontal air bag systems have occupant sensors

that provide information such as seat position, occupant presence, seat

belt use, and identification of a child seat. However, occupant sensors

currently available in U.S. market vehicles are not capable of

distinguishing among different sizes of occupants, such as whether the

passenger is a child or an adult. A limited number of vehicles with

multistage air bags contain seat position sensors on the driver side that

identify whether the seat is forward or rearward on the seat track. If the

seat is positioned forward, indicating that the driver is seated close to the

steering wheel and the air bag module, the system deploys the air bag with

reduced force. Some vehicle models contain weight-based sensors on the

passenger side that identify whether the seat is occupied. If the sensor

does not detect an occupant over a specified weight, the system

deactivates the passenger air bag. These sensors are intended to prevent

unnecessary deployment of the passenger air bag. Some vehicle models

also contain, as part of their multistage air bag systems, seat belt use

sensors on the driver and passenger sides that identify if the occupant is

wearing the seat belt. The system deploys the air bags at a higher crash

velocity threshold if the occupant is buckled and a lower threshold if the

occupant is unbuckled. Finally, a limited number of vehicles with

multistage air bags contain child seat sensors that identify a tag in the

bottom of a compatible child seat. The system deactivates the passenger

air bag when it detects the tag. NHTSA considers these child seat sensors

to be an excellent supplement to other occupant classification systems.

However, NHTSA will not allow manufacturers to use this sensing system

alone to comply with the rule’s requirements because it would be difficult

to ensure that tags would be properly installed on the wide variety of child

seats used by the general public. (See app. III for information on the types

of occupant classification sensors installed in model year 2001 and early

model year 2002 vehicles with multistage air bags.)

Anticipated improvements: To comply with the advanced air bag rule,

manufacturers anticipate increasing the use of driver seat position sensors

and driver and passenger seat belt use sensors. In addition, sensors based

on weight classification and/or pattern recognition will be installed on the

passenger side to distinguish among adults, children, and child seats.

Technologies being considered primarily include load cells, pressure

Occupant Classification

Sensors
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 39 GAO-01-596 Vehicle Safety

bladders, and pattern/pressure mats.1 Load cells are electro-mechanical

devices located at each attachment point of the seat frame to the vehicle.

They estimate the force applied to the seat, allowing the system to classify

an occupant based on their seated weight. A pressure bladder is a fluid- or

air-filled bladder located under the seat cushion and above the seat frame.

The system classifies an occupant based on the amount of pressure

applied to the bladder. A pattern/pressure mat contains multiple sensor

elements and is located between the seat cushion and upholstery. The

system classifies an occupant based on the amount of pressure applied to

the mat and the pattern of the occupant’s imprint on the seat. Some of

these technologies may need to be augmented by seat belt tension sensors

to identify whether the amount of force applied to the seat is due in part to

the seat belt rather than the occupant’s weight. This is important

information for identifying child seats. Occupant position sensors, which

are described in the section below, may also be used to enhance occupant

classification sensors.

Description: This central processing unit stores the vehicle’s sensing

algorithms, computational systems that interpret and analyze inputs from

the crash sensors and occupant sensors to determine whether the air bag

should be deployed and, if so, what level of deployment is appropriate. In

order to deploy the air bags in time to restrain the occupants, the control

module must predict during the initial part of the crash whether a crash is

occurring that exceeds a predetermined severity threshold. The control

module generally triggers deployment from 10 to 100 milliseconds after the

start of the crash, depending on the type of crash.

Advanced technologies currently available: Multistage air bag systems

contain control modules with sensing algorithms of increased complexity

that can determine the appropriate level of air bag deployment, based on

available inputs. In multistage air bag systems that include occupant

sensors and/or multipoint crash sensing systems, the algorithms process

the additional inputs provided by these sensors in making deployment

decisions.

Anticipated improvements: To comply with the advanced air bag rule,

control modules will require algorithms of greater complexity that will be

able to interpret and analyze additional inputs concerning crash scenarios

 1

Manufacturers are also considering other technologies, such as capacitive coupling

sensors, which are embedded in the seat cushion and classify the occupant by detecting the

disruption in a low energy electric field.

Control Module
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 40 GAO-01-596 Vehicle Safety

and types of occupants and use this information in making appropriate

deployment decisions. Manufacturers also intend to make further

improvements in control modules to increase the speed of processing of

inputs and the accuracy of deployment decisions. As algorithms become

more complex, it may be necessary in the longer term to move from a

centralized control module to a system in which the processing and

decision-making functions are decentralized, because of dramatic

increases in the amount of information being input and in the

computations needed.

Description: Multistage inflators have two charges that can generate two

or more stages of inflation. Firing one charge generates low-level

deployment; firing both charges simultaneously or in sequence generates

higher levels of deployment.

Advanced technologies currently available: A number of vehicle models

currently have frontal air bag systems with multistage inflators. Most of

these vehicles have inflators with two stages of inflation (low- and highlevel deployment), while a limited number have inflators with three stages

of inflation (low-, medium-, and high-level deployment). In most cases, the

multistage inflators are on both the driver and passenger sides, but in

some cases only the passenger side has a multistage inflator. In currently

available multistage air bag systems, the deployment level is triggered

based on crash severity and, in some cases, driver seat position. In

addition, as previously explained, some of these systems deploy the air

bags at different crash severity thresholds for belted or unbelted

occupants and/or deactivate the passenger air bag if a sensor detects that

the passenger seat is empty or contains a child seat. (See app. III for

information on the multistage air bag systems installed in model year 2001

and early model year 2002 vehicles.)

Anticipated improvements: To comply with the advanced air bag rule,

manufacturers will use multistage inflators with two or more stages of

inflation. Some manufacturers have told us that their introduction of

inflators with more than two stages of inflation depends on further

advancements in crash sensors, occupant sensors, and the control module

in order to be able to reliably determine the appropriate level of inflation.

Various inflation technologies are under development that may provide

continuous variation in inflation, rather than inflation in discrete stages,

allowing greater adaptiveness to inputs provided by crash and occupant

sensors. For example, one such technology would use a variable electric

current to continuously control the rate of gas generation during inflation

of the air bag. Inflators with these technologies may be introduced by

Multistage Inflators
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 41 GAO-01-596 Vehicle Safety

some manufacturers during the 3-year phase-in period for complying with

the advanced air bag rule.

Description: In addition to characteristics of the inflators, some air bag

design features can reduce the aggressivity of the deploying air bag and,

therefore, the likelihood of serious injury caused by deployment. These

features include the location of the air bag module (which contains the

inflator and the air bag) and characteristics of the bag itself, such as

folding, shape, compartments, tether straps, and venting.

Advanced technologies currently available: Manufacturers have made a

variety of changes in bag design in order to make deployment less likely to

cause injury. The location, folding, and shape of frontal air bags have been

major areas of design change. On the driver’s side, air bag modules have

been recessed into the steering wheel in many vehicles to add space

between the driver and the deploying air bag. Also, many driver air bags

now have a fold pattern and shape that allows the bag to deploy in a radial

manner, so that the initial “burst out” inflation force will inflate the bag

laterally rather than rearward toward the driver. On the passenger’s side,

manufacturers often locate the bag module in a “top-mount” position on

the instrument panel, to increase the distance between the occupant and

the deploying bag, or use a smaller-sized bag if it is located in a “midmount” position in front of the passenger on the instrument panel.

Some newer fold and shape designs and venting schemes can make the

deploying air bag adaptive to the position of the occupant. For example,

some passenger air bags in use today contain a fabric flap attached to the

bag, known as a “bias flap,” which directs the initial burst out inflation of

the bag to the side of and away from the occupant if he or she is out of

position (in close proximity to the bag) at the time of deployment. Some

bags have variable venting designs that inflate the bag more softly if it is

obstructed during deployment, indicating that the occupant is out of

position. Tethers, which are strips of fabric connecting the front and back

panels of the bag, have been incorporated into some bag designs on both

the driver and passenger sides to reduce extension of the bag and help

position it more quickly when it is deployed.

Anticipated improvements: Although air bag design is a relatively mature

technology, manufacturers and air bag suppliers continue to work on

improvements in this area in order to enhance the ability of air bag

systems to comply with the advanced air bag rule. Concepts under

development that may become available in the longer term include venting

systems that will work with multistage inflators to increase the

Air Bag Features That

Minimize Risk to

Occupants
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 42 GAO-01-596 Vehicle Safety

adaptability of deployment (by controlling inflator output based on input

from sensors) and bags with multiple compartments that inflate

sequentially.

Description: These sensors are intended to determine the proximity of an

occupant to the air bag. Sensing devices installed in the interior of the

vehicle would enable the system to suppress the air bag if an occupant is

out of position and too close to the air bag.

Anticipated technologies: Infrared, ultrasonic, capacitive, and optical

technologies are being researched to develop “dynamic” sensors that can

continuously track an occupant’s position with respect to the air bag

module. Infrared sensors utilize an array of invisible infrared light beams

projected across the passenger compartment to identify the position of an

occupant. For ultrasonic sensors, ultrasonic transducers emit sound waves

and the sensors monitor the sound waves that are reflected by an

occupant. Capacitive sensors utilize an electric field to identify the

position of an occupant by detecting moisture in the body and optical

sensors monitor the position of an occupant. While “static” ultrasonic

sensors that periodically determine the occupant’s position may be

installed on a limited basis to augment occupant classification sensors

before 2003, researchers are not yet certain whether or when dynamic

occupant position sensing will become widely used.

Description: These sensors would identify the position, approach angle,

velocity, and mass of objects prior to a collision and allow more time for

the air bag system to respond.

Anticipated technologies: Radar (radio wave) is the principal technology

being researched. Precrash sensing technologies are still in the early

stages of research to determine if the concept is feasible. Therefore, it is

not yet clear whether or when this technology might become available.

The primary challenge in developing this technology is identifying the

Additional

Enhancements to

Advanced Air Bag

Systems Anticipated

for the Longer Term

Occupant Position Sensors

Precrash Sensors
Appendix IV: Current Availability of and

Anticipated Improvements in Advanced Air

Bag Technologies

Page 43 GAO-01-596 Vehicle Safety

mass of an object in the path of the vehicle. “Adaptive cruise control,”

which automatically reduces a vehicle’s speed to maintain a safe distance

to vehicles in front, is currently available on some vehicles and is

considered by some to be a precursor of precrash sensing.

(348239)