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Status Report, Vol. 36, No. 3 | SPECIAL ISSUE: CRASHWORTHINESS IMPROVEMENTS | March 20, 2001 Subscribe

Crashworthiness keeps getting better

Automakers are paying attention to the results of the Institute's 40 mph frontal offset crash tests, and vehicle ratings prove it. They're getting better. Fewer than one among every four 1995-98 cars and passenger vans tested by the Institute earned a good overall crashworthiness evaluation based primarily on performance in the offset test. About half of all 1999-2001 models tested earned good ratings.

In large part, this is because auto manufacturers now are incorporating offset crash test performance plus government-required and consumer information crash tests into their design guidelines for new and redesigned passenger vehicles.

Among 32 updated vehicle designs the Institute has tested since 1995, a total of 20 boosted their ratings in the offset test compared with ratings for predecessor models (see attached ratings chart). Not included among the 20 are vehicles that earned good overall ratings the first time around, so the ratings for their redesigned versions couldn't get any higher. Three consecutive Taurus designs (1995, 1996, and 2000) earned the Institute's highest rating. So did the 1997 Lexus LS 400 and its successor model, the 2001 LS 430. The 1996 and 1999 Ford Windstar both rated good overall.

The Institute assigns good, acceptable, marginal, or poor crashworthiness ratings based primarily on a vehicle's performance in the offset test. Crashworthiness refers to how well a vehicle protects its occupants in a crash, and the ratings are based on measurements of occupant compartment intrusion, injury measures taken from the driver dummy during the test, and judgments of how well the restraint system works to control dummy movement.

Early improvers include Toyota and Volkswagen models

Among the first manufacturers to demonstrate improved performance in the offset test were Toyota and Volkswagen. The 1996 Toyota Previa (passenger van) and 1995 Volkswagen Passat (midsize car) earned poor overall evaluations, but their successor models introduced in 1998, the Toyota Sienna and redesigned Passat, improved to good ratings based on their offset crash test performances (see Status Report special issue: safety advancements, April 24, 1999). Since then, 18 other redesigned models have posted higher crashworthiness ratings than their predecessors.

Structural performance is key

The most important aspect of the offset test is how well a vehicle's front-end crush zone absorbs energy and, in turn, how well the occupant compartment, or safety cage, holds together during the crash.

"If the occupant compartment remains largely intact, then the restraint system can do its job of controlling the dummy's motion and keeping the injury measures low. But if there's significant intrusion, then the restraint system is less likely to keep injurious forces low," Institute president Brian O'Neill explains.

Four more examples

A predecessor model of the 2001 Dodge Stratus, the 1995 Chrysler Cirrus, rated poor in the offset test because the safety cage all but collapsed during the impact. The car's roof buckled, the instrument panel moved rearward into the driver space about 20 centimeters, and the steering column moved rearward 16 centimeters. Footwell intrusion contributed to high injury measures on both of the driver dummy's lower legs.

In contrast, the 2001 Dodge Stratus ("twin" model of the Cirrus) came through the 40 mph offset test with far less safety cage deformation. There was significantly less rearward intrusion of the footwell and the instrument panel. This, together with reduced rearward movement of the steering column, enabled the restraint system to control dummy movement, which in turn improved the injury measures recorded on the dummy.

"There were a lot of things we did learn from [the Institute's] previous test," Matt Reynolds of DaimlerChrysler points out. "We added some front stiffness and rigidity in the safety cage, changed the way we distribute loads in an event through the car, made frontal impact protection more robust, improved the side impact protection, stiffened the A-pillar, and enhanced the sill in the underbody design."

Another good example is the Cadillac Seville, which improved from a rating of poor for the 1997 model to good for the redesigned 2000 model. To evaluate the structural performance of a vehicle, Institute engineers measure intrusion into the occupant compartment in 10 places including the A-pillar, instrument panel, steering column, and footwell. In the 2000 model Seville, all 10 intrusion measures improved dramatically compared with the 1997 Seville's performance.

Toyota has improved the Avalon twice. A 1996 model rated only marginal in the Institute's 40 mph offset test. A 1998 model improved to acceptable. The 2000 Avalon topped its predecessor models, earning a good overall rating in large part because the car's structure held up so well in the offset test. Intrusion measures were low.

Another improved car, the Honda Civic, boosted its rating from acceptable (1997) to good for the redesigned 2001 model. In the test of the earlier version of the Civic, moderate intrusion was recorded. Moderately high injury measures recorded on the dummy indicated the possibility of chest and left leg injuries. These problems were eliminated in the 2001 Civic. According to Honda's Tomiji Sugimoto, the new model's increased occupant compartment stiffness and greater engine-room energy absorption capacity are behind the improvements.

Old: 1995 Chrysler Cirrus

1995 Chrysler Cirrus

The occupant compartment of this 1995 Chrysler Cirrus all but collapsed during the offset test. There was massive intrusion, leaving very little space for the driver dummy.

Improved: 2001 Dodge Stratus

2001 Dodge Stratus
2001 Dodge Stratus

When the redesigned 2001 Dodge Stratus (a "twin" of Cirrus) was tested, the occupant compartment remained intact. Intrusion was much less, leaving more space for the driver dummy.

Measures of occupant compartment intrusion (cm), 40 mph frontal offset test

A-pillar movement rearward Footwell intrusion Brake pedal intrusion Instrument panel movement Steering column movement
Left Center Right Footrest Left Right Upward Rearward
2001 Dodge Stratus 1 22 24 16 10 16 3 2
9 2
1995 Chrysler Cirrus 25 39 39 35 34 36 21 20 6 16

Old: 1997 Cadillac Seville

1997 Cadillac Seville
1997 Cadillac Seville

Improved: 2000 Cadillac Seville

2000 Cadillac Seville
2000 Cadillac Seville

Measures of occupant compartment intrusion (cm), 40 mph frontal offset test

A-pillar movement rearward Footwell intrusion Brake pedal intrusion Instrument panel movement Steering column movement
Left Center Right Footrest Left Right Upward Rearward
2000 Cadillac Seville 3 17 15 16 6 9 4 3 4 2
1997 Cadillac Seville
9 31 37 31 21 31 16 16 15 11

NCAP performances improve too

The federal New Car Assessment Program (NCAP) has documented major improvements. Since 1978, this crash test program has provided consumers with comparative vehicle safety ratings of cars sold in the United States.

The NCAP test involves the full width of a moving vehicle hitting a concrete barrier at 35 mph. Such a configuration is relatively demanding of occupant restraint systems, but it's not as demanding of vehicle structure, compared with the Institute's 40 mph offset test, because the energy of the impact is distributed across a vehicle's entire front end.

By setting a higher benchmark than the minimum safety standards all cars are required to meet, NCAP encourages crashworthiness improvements, particularly in occupant restraints. In general, restraint systems now are much better than those in cars when NCAP began more than 20 years ago. Today's safety belts and airbags are designed to work together. Newer models are equipped with belt designs that limit forces on occupants' chests and crash tensioners that prevent belt slack from allowing excessive forward motion in a crash. Many of these and other improvements result directly from the dynamic testing of restraint systems that began with NCAP.

Crashworthiness ratings not confined to United States

Other new car rating programs cover vehicles sold outside the United States. EuroNCAP and Australia's NCAP include a frontal offset test into a deformable barrier, similar to the Institute's offset test but with different rating criteria. Japan uses a full-width rigid barrier test and will add an offset test. All three of these programs also include side impacts. EuroNCAP adds a pedestrian impact and, for vehicles with dynamic head protection (airbags) in side impacts, a side-into-pole test.

"We're mostly seeing examples of improved crashworthiness, which demonstrate that the car companies are responding to our crash test results and the results of other tests conducted worldwide," O'Neill says. "These improvements don't automatically occur from one model to the next. They happen because the structural designs of cars are being improved, which in turn means better performance in a range of serious frontal crashes, including the Institute's offset test."

SIDEBAR
Crash tests can reveal safety defects
The Institute's crash tests occasionally expose defects or other specific problems, prompting automakers to make midyear fixes or sometimes issue a recall.
Some vehicles still languish

Despite paying closer attention to crashworthiness, not all automakers are making fleetwide improvements.

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