IIHS Says Its Crash Test Study Suggests Small Cars Can’t Protect People in Front-to-Front Crashes as Well as Bigger, Heavier Models
14 April 2009
Three 40 mph car-to-car front-to-front crash tests, each involving a microcar or minicar into a midsize model from the same manufacturer, indicate that extra vehicle size and weight enhance occupant protection in such collisions, according to the Insurance Institute for Highway Safety, which ran the testing. A summary of the study is published in the 14 April IIHS Status Report.
The choice of midsize cars reveals how much influence some extra size and weight can have on crash outcomes, the Institute said. The Institute chose pairs of 2009 models from Daimler, Honda, and Toyota because these automakers have micro and mini models that earn good frontal crashworthiness ratings, based on the Institute’s offset test into a deformable barrier.
Researchers rated performance in the 40 mph car-to-car tests, like the front-into-barrier tests, based on measured intrusion into the occupant compartment, forces recorded on the driver dummy, and movement of the dummy during the impact.
|IIHS video. Click to play.|
The Honda Fit, Smart Fortwo, and Toyota Yaris are good performers in the Institute’s frontal offset barrier test, but all three are poor performers in the frontal collisions with midsize cars. Although the physics of frontal car crashes usually are described in terms of what happens to the vehicles, injuries depend on the forces that act on the occupants, and these forces are affected by two key physical factors, the Institute said.
One is the weight of a crashing vehicle, which determines how much its velocity will change during impact. The greater the change, the greater the forces on the people inside and the higher the injury risk. The second factor is vehicle size, specifically the distance from the front of a vehicle to its occupant compartment. The longer this is, the lower the forces on the occupants.
Size and weight affect injury likelihood in all kinds of crashes. In a collision involving two vehicles that differ in size and weight, the people in the smaller, lighter vehicle will be at a disadvantage. The bigger, heavier vehicle will push the smaller, lighter one backward during the impact. This means there will be less force on the occupants of the heavier vehicle and more on the people in the lighter vehicle. Greater force means greater risk, so the likelihood of injury goes up in the smaller, lighter vehicle.
|Driver deaths per million 1-3-year-old cars registered, 2007. Source: IIHS. Click to enlarge.|
Crash statistics confirm this, the Institute said, noting that driver deaths per million 1-3-year-old minicars in multiple-vehicle crashes during 2007 was almost twice as high as the rate in very large cars. (The rate for small cars—larger than minicars—was even higher than the driver death rates for minis, while the driver death rate for large cars was higher than that for midsize cars.)
The death rate per million 1-3-year-old minis in single-vehicle crashes during 2007 was 35 compared with 11 per million for very large cars. Even in midsize cars, the death rate in single-vehicle crashes was 17% lower than in minicars. The lower death rate is because many objects that vehicles hit aren’t solid, and vehicles that are big and heavy have a better chance of moving or deforming the objects they strike. This dissipates some of the energy of the impact.
Honda Accord versus Fit: The structure of the Accord held up well in the crash test into the Fit, and all except one measure of injury likelihood recorded on the driver dummy’s head, neck, chest, and both legs were good. In contrast, a number of injury measures on the dummy in the Fit were less than good. Forces on the left lower leg and right upper leg were in the marginal range, while the measure on the right tibia was poor. These indicate a high risk of leg injury in a real-world crash of similar severity. In addition, the dummy’s head struck the steering wheel through the airbag. Intrusion into the Fit’s occupant compartment was extensive. Overall, this minicar’s rating is poor in the front-to-front crash, despite its good crashworthiness rating based on the Institute’s frontal offset test into a deformable barrier. The Accord earns good ratings for performance in both tests.
Mercedes C class versus Smart Fortwo: After striking the front of the C class, the Smart went airborne and turned around 450 degrees. This contributed to excessive movement of the dummy during rebound—a dramatic indication of the Smart’s poor performance but not the only one. There was extensive intrusion into the space around the dummy from head to feet. The instrument panel moved up and toward the dummy. The steering wheel was displaced upward. Multiple measures of injury likelihood, including those on the dummy’s head, were poor, as were measures on both legs.
In contrast, the C class held up well, with little to no intrusion into the occupant compartment. Nearly all measures of injury likelihood were in the good range.
Toyota Camry versus Yaris: There was far more intrusion into the occupant compartment of the Yaris than the Camry. The minicar’s door was largely torn away. The driver seats in both cars tipped forward, but only in the Yaris did the steering wheel move excessively. Similar contrasts characterize the measures of injury likelihood recorded on the dummies. The heads of both struck the cars’ steering wheels through the airbags, but only the head injury measure on the dummy in the Yaris rated poor. There was extensive force on the neck and right leg plus a deep gash at the right knee of the dummy in the minicar. Like the Smart and Fit, the Yaris earns an overall rating of poor in the car-to-car test. The Camry is acceptable.
There are good reasons people buy minicars. They’re more affordable, and they use less gas. But the safety trade-offs are clear from our new tests. Equally clear are the implications when it comes to fuel economy. If automakers downsize cars so their fleets use less fuel, occupant safety will be compromised. However, there are ways to serve fuel economy and safety at the same time.—IIHS President Adrian Lund
Lund said that the structure of the new fuel economy standards for MY 2011—which use a size-based system rather than a fleet average and which will mandate lower fuel consumption as cars get smaller and lighter—will remove the incentive for automakers to downsize their lightest vehicles to comply with CAFE. It also could mean, he noted, that technology currently used to enhance horsepower would go instead to reduce gas consumption—a direct safety benefit because less powerful cars have lower crash rates.
Another way to conserve fuel, and serve safety at the same time, the Institute said, is to set lower speed limits. Going slower uses less fuel to cover the same distance. The national maximum 55 mph speed limit, enacted in 1974, saved thousands of barrels of fuel per day. It also saved thousands of lives. Highway deaths declined about 20% the first year, from 55,511 in 1973 to 46,402 in 1974. The National Research Council estimated that most of the reduction was due to the lower speed limit, and the rest was because of reduced travel. By 1983 the national maximum 55 mph limit still was saving 2,000 to 4,000 lives annually.
Fifty-five was adopted to save fuel, but it turned out to be one of the most dramatic safety successes in motor vehicle history. The political will to reinstate it probably is lacking, but if policymakers want a win-win approach, lowering the speed limit is it. It saves fuel and lives at the same time.—Adrian Lund
The president of smart USA, Dave Schembri, issued a statement related to the Insurance Institute’s test:
This non-standard crash test performed by the Insurance Institute for Highway Safety (IIHS) simulates a crash situation that is rare and extreme. The test used an extremely high crash severity which is unlikely to occur in real world crashes. In fact, less than 1% of all crashes fall within these parameters.
The test conducted by the IIHS was not consistent with how federal regulators evaluate vehicles in crash tests. The National Highway Traffic Safety Administration (NHTSA) requires that cars and trucks of all sizes meet stringent safety requirements.
The smart fortwo meets or exceeds all US government crash test standards, including a 5-star side crash rating, and previously earned the highest scores for front and side crash worthiness from the IIHS in its standard test. The smart fortwo is equipped with advanced crash avoidance and crash protection safety systems, including electronic stability program (esp), and a reinforced steel safety cage called a tridion safety cell, which is standard equipment on all models.
For the past decade, smart has a proven track record of safety with approximately one million cars on the road in 37 countries. People drive small cars for many reasons, not just fuel economy as the IIHS states. People choose small vehicles because they are generally more environmentally friendly, a great value, they provide for greater driving and parking options in congested urban areas and many consumers tell us they are simply more fun to drive.
IIHS Status Report, Vol. 44, No. 4, April 14, 2009
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