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Status Report, Vol. 41, No. 1 | January 28, 2006 Subscribe

Automakers' efforts reduce mismatch between cars and light trucks

Mismatch of the front ends of the vehicles in this crash test is a problem. The SUV's front-end energy-absorbing structure rides over the car's. In a real crash, this could increase injury risks for the car occupants, which is why auto manufacturers have been committed since 2003 to designing the front ends of light trucks (SUVs and pickups) so their energy-absorbing structures overlap those of cars (see "Automakers pledge series of steps to improve crash compatibility," Jan. 3, 2004).

"Compliance with these voluntary commitments already is making a difference, even though automakers don't have to ensure that all of their light trucks comply until the 2010 model year," says former Institute president Brian O'Neill, lead author of a new study that quantifies the benefits of the commitments. Car driver death rates were lower — in some cases dramatically lower — during 2001-04 in front and side crashes with 2000-03 model SUVs and pickups that already met the automakers' commitments, compared with car driver death rates in crashes with light trucks that didn't.

This is the first time researchers have compared death rates in cars in crashes with complying versus noncomplying SUVs and pickups. A previous Institute study considered potential benefits for car drivers in frontal crashes with light trucks if the trucks' front ends had been the same as those of cars of the same weight (see Status Report special issue: vehicle incompatibility in crashes, April 28, 2005).

Front-to-front crash
Estimated fatality risk
reductions for car drivers
Car driver belt use Risk reduction
SUV and car Belted 18 to 21%
Unbelted 2 to 3%
Pickup and car Belted 9 to 19%
Unbelted -3 to 4 %
Front-to-side crash
Estimated fatality risk reductions for car drivers
Risk reduction
SUV into car 47 to 48%
Pickup into car 1 to 9%

What the automakers agreed to do

Recognizing the importance of preventing override and underride in head-on crashes between cars and SUVs or pickups, automakers committed to increasing the geometric overlap of the front energy-absorbing structures of light trucks and cars.

To meet this commitment, automakers are designing the primary energy-absorbing structures of new SUVs and pickup trucks to overlap at least 50 percent of the federally mandated bumper height zone for cars. Alternatively, automakers may elect to connect a second energy-absorbing structure to the primary one. Then the lower edge of the secondary structure cannot be any higher than the bottom of the car bumper zone.

By September 2009 all new light trucks for sale in the U.S. market will be designed to meet one of these alternatives. The auto manufacturers have agreed to other commitments to address vehicle incompatibilities in front-to-side crashes.

Institute researchers collected information on compliance with front-end matching agreements from 13 automakers to directly assess the benefits for drivers of cars in crashes with light trucks that are in compliance versus those that don't yet comply. The manufacturers that provided information for the study are Audi, BMW, DaimlerChrysler, Ford, General Motors, Honda, Hyundai, Mazda, Mitsubishi, Nissan, Porsche, Toyota, and Volvo. Two other automakers, Isuzu and Subaru, are participating in the voluntary commitments to improve vehicle compatibility but couldn't provide compliance data in time for the study.

The researchers obtained information from the federal Fatality Analysis Reporting System on crashes during 2001-04 in which 2000-03 model SUVs or pickups struck cars head-on or on the driver side, resulting in car driver deaths. Researchers computed the relative risks of car driver deaths in crashes with complying versus noncomplying SUVs and pickups, based on observed numbers of deaths in crashes with complying vehicles versus expected numbers of deaths if the complying light trucks had the same car driver death rates as noncomplying ones.

Death rates were computed according to the weights of the SUVs and pickups involved in the crashes in which car drivers died. Because so few deaths occurred in cars struck by the lightest and heaviest SUVs and pickups, computations were limited to those weighing 3,000 to 6,000 pounds.

Belted drivers benefit in frontal crashes

The fatality risk was lower for belted car drivers in front-to-front crashes with complying SUVs and pickups, compared with noncomplying ones. In crashes with SUVs, the risk was 18-21 percent lower if the SUV was in compliance with the automakers' commitments. In crashes with complying pickups the estimated risk reduction was 9-19 percent (ranges reflect the uncertainty caused by the small numbers of car driver deaths in each crash type).

For unbelted car drivers, the fatality risk wasn't reduced if the light trucks complied with the commitments. That is, death rates for car drivers who didn't buckle up were about the same, whether or not the trucks involved in the head-on crashes complied.

Benefits in side impacts

The design changes to improve front-end compatibility between light trucks and cars are specifically intended to enhance car occupant protection in head-on crashes with SUVs and pickups. The analyses by Institute researchers indicate that some benefits are accruing in side impacts too.

When SUVs struck cars on the driver side, the estimated fatality risk reduction for the car drivers, belted and unbelted, was 47-49 percent when the striking SUVs were in compliance versus when they weren't. The risk reduction was a more modest 1-9 percent for drivers whose cars were struck on the side by complying pickup trucks compared with noncomplying ones. (Note: Death rates weren't computed separately for belted and unbelted car drivers in front-to-side crashes because of the relatively low effectiveness of safety belts in side impacts. Plus the number of unbelted car driver deaths in side impacts was too small to consider separately.)

It's likely that the big fatality risk reduction for complying SUVs that strike the sides of cars, but not for striking pickups, may reflect some other design aspects that also are important. For example, the front ends of many of the SUVs in the Institute's analyses, both complying and noncomplying, are less vertical and more rounded than the fronts of pickups. The combination of lower structures and less vertical front ends could be accounting for the large risk reductions for drivers of cars struck in the sides by SUVs. But the dataset for the study wasn't big enough to address this aspect of front-end design.

"What's important from this study is the encouraging evidence that the voluntary design changes are reducing incompatibilities between SUVs and pickup trucks in front-to-front crashes with cars," O'Neill concludes.

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