ARLINGTON, Va. — The Kia Sedona and Subaru Impreza are the best performers in a group of minivans and small cars recently evaluated by the Insurance Institute for Highway Safety. The Sedona is the first minivan to earn the Institute's Top Safety Pick award, and the Impreza is only the second small car design to earn this award. Both vehicles earn gold awards for good crashworthiness ratings.
The Institute also evaluated the Toyota Prius hybrid's front, side, and rear crashworthiness plus the side crashworthiness of three other vehicle designs — the Mini Cooper (small car) and Dodge Grand Caravan and Chevrolet Uplander (minivans). Results for these vehicles update the results for minivan and small car models that were released last year. Side tests of the Grand Caravan, Uplander, Mini Cooper, and Impreza were delayed at the request of the vehicle manufacturers, who were making changes to improve crashworthiness.
Criteria for Top Safety Pick award: Front, side, and rear crashworthiness ratings
Frontal evaluation must be GOOD, based on performance in 40 mph frontal offset crash test into deformable barrier
Side evaluation must be GOOD, based on performance in test in which driver side is struck by barrier representing front of SUV or pickup truck
Rear evaluation must be GOOD for gold award or ACCEPTABLE for silver award, based on head restraint geometry and test performance of seat/head restraint
Sedona is top-rated minivan
Among the eight current minivan designs the Institute has rated, the Sedona is the only one that earns good ratings in all three Institute tests (this vehicle also will be sold as the 2007 Hyundai Entourage later this spring). The new Sedona's frontal crash test performance is an improvement compared with the previous model, which the Institute rated acceptable.
"The Sedona is the best minivan we've tested," says Institute president Adrian Lund. "Other minivans have earned good front and side ratings, but they haven't achieved a satisfactory level of rear crash protection. The Sedona stands out as the first to get a clean sweep of good ratings across the board."
In the frontal test, the Sedona's structure held up well. There was little intrusion into the occupant compartment. The dummy's movement was well controlled, and injury measures were low. In the side test, curtain-style airbags prevented the heads of driver and rear passenger dummies from contacting the intruding barrier. The Sedona is one of five current minivan models with standard side airbags designed to protect the heads of people in all three rows of seats. For protection in rear impacts, the Sedona is a standout. Its seat/head restraints protect front-seat occupants' necks.
"Many manufacturers haven't paid as much attention to occupant protection in rear crashes, compared with front and side crashes," Lund points out. "Kia deserves credit for designing the Sedona's seat/head restraints for protection in one of the most common kinds of commuter traffic crashes."
The Kia is the only minivan the Institute has evaluated that's equipped with active head restraints. These are designed to move up and toward the back of the head during a rear impact. As an occupant's torso sinks into the Kia seat during a rear-end crash, a mechanism in the seatback is designed to move the head restraint so it's more likely to be in a good position to catch the head, keeping it and the torso moving together.
The most common kind of injuries reported from crashes are neck injuries, and these are most likely to occur in rear impacts. Whiplash is the most serious injury reported in about 2 million insurance claims each year. Such claims cost at least $8.5 billion annually.
Subaru is a gold standard among small cars
Just as manufacturers made major improvements in how their vehicles protect people in frontal crashes, now they're making similar improvements for side and rear impact protection. Subaru reinforced the pillar behind the rear passenger door and upgraded the side airbags to standard in the 2006 Impreza. This car also has head restraints that do a better job than those in other small cars. The Impreza is a good performer in all three Institute tests (front, side, and rear) and earns the gold Top Safety Pick award. Its results also apply to the Saab 9-2X, which is based on the Impreza design.
"Subaru was one of the manufacturers that last year asked us to delay side testing because of vehicle design changes that were in progress," Lund says. "It's not uncommon for us to grant such requests as long as the design changes will be made in production models within a reasonable time. The goal of our crash test program is to encourage these kinds of improvements to reduce injury risk in real-world crashes."
Top Safety Pick winners represent an elite fraction of the car market. Winners of the gold award have earned good ratings in the Institute's frontal offset and side impact tests, and their seat/head restraints are rated good for protection against neck injuries in rear impacts. Awards are by vehicle size because both size and weight influence occupant protection in serious crashes. Larger, heavier vehicles generally afford more protection than smaller, lighter ones. The Top Safety Pick award indicates a better choice for safety within a size class, but a small car that earns this award doesn't necessarily afford better protection than a larger car that doesn't.
First Institute test of a hybrid
The Toyota Prius was a good performer in the frontal crash test and, equipped with optional side airbags, also good in the side test. But it's rated marginal for seat/head restraint design, so it isn't a Top Safety Pick. The movement of the driver dummy was reasonably well controlled during the frontal test. Although the dummy's head did hit the pillar between the doors and the roof rail, head accelerations were low. Other injury measures also were low, and the Prius's structure held up with minimal intrusion into the occupant compartment.
"The way a hybrid model earns the top rating in the frontal test is the same way any other car does," Lund says. "Its front structure has to crush to absorb crash energy, and it has to have a safety cage that stays intact so the safety belts and airbags can protect the occupants."
The Institute conducted two side tests of the Prius, with and without its optional head-protecting side airbags. Without the airbags the Prius earns the lowest rating of poor. The intruding barrier struck the driver dummy's head. Measures recorded during the crash indicate that a serious skull fracture and brain injuries would be likely to occur in a real-world crash of similar severity.
"The result for the Prius with its optional side curtain airbags was dramatically different," Lund says. "This time the airbag kept the dummy's head from being struck by the barrier, and injury measures all were low. These results show the importance of head-protecting side airbags in reducing the risks for car occupants, especially when their vehicles are struck in the side by a pickup or SUV."
Another important aspect of crashworthiness is how well seat/head restraints protect people from whiplash in rear impacts. The ones in the Prius earn the second lowest rating of marginal. They can be positioned high enough and close enough to the backs of most people's heads, but good geometry alone isn't enough to provide adequate protection from whiplash. Seats and head restraints have to work together to protect the neck, and the Institute's test indicates that in a real-world crash the seats in the Prius wouldn't keep the forces on the neck as low as in other vehicles.
When a vehicle is struck in the rear and driven forward, the vehicle seats accelerate the occupants' torsos forward. Unsupported, their heads will lag behind the forward movement of their torsos. This differential motion causes the neck to bend back and stretch. The higher the torso acceleration the more sudden the motion, the higher the forces on the neck, and the more likely a neck injury is to occur.
"If a seat is too stiff, without enough 'give' to it so a person sinks into it during a crash, then the head restraint can move back and away from the head. This can lead to higher forces on the neck, and whiplash injury is more likely," Lund notes.
For most vehicles with hybrid variants, the Institute's ratings apply to both the hybrid and conventional versions. These vehicles include the Honda Civic and Accord, Lexus RX, and Toyota Highlander. The Prius is sold only as a hybrid.
Uplander minivan is poor performer in side test
The Institute tested the Chevrolet Uplander with and without its optional side airbags (results apply to similar Buick, Pontiac, and Saturn models). In both tests there were problems with the seats in the middle row. With the optional side airbags, all four attachment points for the seat occupied by the rear passenger dummy completely dislodged. The seat broke free. In the second test without side airbags, one attachment point released and a second one broke, allowing partial separation of the seat from the floor.
"This didn't worsen the injury measures recorded on the rear dummy, but a real person in a more complicated real-world crash might not fare as well. Seats should stay attached because they're part of the restraint system, and in real crashes vehicles may roll over or be hit again," Lund explains. If this hadn't happened, the Uplander with optional side airbags would earn a rating of acceptable for protection in side impacts. The seat problem downgrades the rating to marginal. Without the optional side airbags, the Uplander is poor regardless of the seat problem.
General Motors engineers have identified a fix for the seats and shown the Institute promising data from a prototype test. When this change has been made in production models, the Institute will test the Uplander again and report the results.
Optional side airbags improve performance of Dodge Grand Caravan
The side test of this minivan was delayed from last year because the manufacturer was working on changes to improve its performance. Beginning with 2006 models (built after December 2005), side airbags were updated, roof and side structures were strengthened, and interior door trim was changed. In the test without optional side curtain airbags, the intruding barrier struck the driver dummy's head. While this didn't produce high injury measures, vehicles should be designed to prevent people's heads from being struck by intruding vehicles, trees, poles, etc.
In contrast, the Grand Caravan with its optional side airbags is rated good for head protection. The curtain-style airbags deploy from above the windows to protect people in all three rows of seats.
"In a side impact, the only thing between the driver and an intruding object is the door and side window. This contrasts with a serious frontal crash, in which the whole length of a vehicle's front end crushes to help protect the people riding in the occupant compartment," Lund points out. "Because there's so little other protection in side crashes, the airbags are especially important. They can provide enough of a cushion to prevent the most serious injuries or reduce their severity."
How vehicles are evaluated
The Institute's frontal crashworthiness evaluations are based on results of 40 mph frontal offset crash tests. Each vehicle's overall evaluation is based on measurements of intrusion into the occupant compartment, injury measures recorded on a Hybrid III dummy in the driver seat, and analysis of slow-motion film to assess how well the restraint system controlled dummy movement during the test.
Each vehicle's overall side evaluation is based on performance in a crash test in which the side of the vehicle is struck by a barrier moving at 31 mph. The barrier represents the front end of a pickup or SUV. Ratings reflect injury measures recorded on two instrumented SID-IIs dummies, assessment of head protection, and the vehicle's structural performance during the impact. Injury measures recorded on two dummies, one in the driver seat and the other in the rear seat behind the driver, are used to determine the likelihood that the driver and/or passenger in a real-world crash would have sustained serious injury to various body regions. The movements and contacts of the dummies' heads during the crash also are evaluated. Structural performance is based on measurements indicating the amount of B-pillar intrusion into the occupant compartment.
Rear crash protection is rated according to a two-step procedure. Starting points are measurements of head restraint geometry — the height of a restraint and its horizontal distance behind the back of the head of an average-size man. Seats with good or acceptable restraint geometry are tested dynamically using a dummy that measures forces on the neck. This test simulates a collision in which a stationary vehicle is struck in the rear at 20 mph. Seats without good or acceptable geometry are rated poor overall because they cannot be positioned to protect many people.