The ratings of good, acceptable, marginal, or poor for 87 current models are based on geometric measurements of head restraints and simulated crashes that together assess how well people of different sizes would be protected in a typical rear crash.
Among the best performers are the seat/head restraint combinations in SUVs made by Subaru and Volvo and new designs from Acura, Ford, Honda, and Hyundai. Seat/head restraints in 3 minivan models from Hyundai and Ford earn good ratings. The redesigned Toyota Tundra is the only pickup model evaluated with seat/head restraints rated good for rear crash protection.
“In stop and go commuter traffic, you’re more likely to get in a rear-end collision than any other crash type,” says David Zuby, senior vice president of the Institute’s Vehicle Research Center. “It’s not a major feat of engineering to design seats and head restraints that afford good protection in these common crashes.”
Rear-end collisions are frequent, and neck injuries are the most common injuries reported in auto crashes. They account for 2 million insurance claims each year, costing at least $8.5 billion. Such injuries aren’t life-threatening, but they can be painful and debilitating.
Keeping heads and torsos together
Good seat/head restraint designs keep people’s heads and torsos moving together: When a vehicle is struck in the rear and driven forward, its seats accelerate occupants’ torsos forward. Unsupported, an occupant’s head will lag behind this forward torso movement, and the differential motion causes the neck to bend 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.
The key to reducing whiplash injury risk is to keep the head and torso moving together. To accomplish this, the geometry of a head restraint has to be adequate – high enough to be near the back of the head. Then the seat structure and stiffness characteristics must be designed to work in concert with the head restraint to support an occupant’s neck and head, accelerating them with the torso as the vehicle is pushed forward.
Kia models excel in rear-end crash tests
The Kia Sedona minivan and Sorento SUV both received the highest possible “good” rating from the Insurance Institute for Highway Safety (IIHS) for rear impact collisions, offering the best protection for people of all sizes in a typical rear-end crash.
“It is becoming well-known that Kia builds safety into all of its vehicles and Sedona and Sorento are just the latest examples to pass independent testing,” said Len Hunt, executive vice president and COO of Kia Motors America (KMA). “We strive to provide our customers with quality vehicles that are equipped with the best available safety features.” The Sedona and Sorento’s standard active head restraints offer optimum and essential passenger neck and back support and protection.
Serving as Kia’s flagship safety vehicle, the Sedona has collected a number of accolades, including receiving the company’s first five-star crash safety rating for each seating position from the National Highway Traffic Safety Administration (NHTSA) when it debuted in 2002, as well as receiving the “Top Safety Pick” from the IIHS for the past two consecutive years.
The current generation Sedona, both long and short wheel bases, tout other standard safety features including six standard air bags (dual advanced front and front seat-mounted side air bags, and full-length side curtain air bags for all three seating rows), a four-channel, four-sensor, antilock brake system (ABS), and a tire pressure monitoring system (TPMS).
Refreshed for 2007 and building off of a five-star crash safety rating from NHTSA for both front and rear side impact crash tests in 2006, the Sorento now has even more standard safety features than its predecessor, offering such standard equipment across all trim lines including advanced two-stage air bags, full-length side curtain air bags, four-wheel disc brakes with ABS, electronic stability control (ESC) and traction control (TCS), tire pressure monitoring system (TPMS), driver knee air bag, and three-point seat belts for all seating positions with adjustable anchors and pretensioners with force limiters in front.
In the latest evaluations, the seat/head restraint combinations in 17 of 59 SUV models are rated good, 5 are acceptable, 14 are marginal, and 23 are rated poor. In minivans, seat/head restraints in 3 models are rated good, 2 are acceptable, 1 is marginal, and 5 are rated poor. In pickups 1 is good, 5 are acceptable, 5 are marginal, and 6 are rated poor.
While there hasn’t been much overall improvement among pickups and minivans since the last time the Institute evaluated protection in rear crashes, the performance of the seat/head restraints in SUVs is much better. In 2006 those in only 6 of 44 SUV models earned a good rating.
“The reason may be that automakers have updated or introduced many new SUVs since 2006, but minivans and pickups are being updated more slowly,” Zuby points out.
In the latest tests seat/head restraints in the Mitsubishi Outlander improved to good from the previous design that was rated acceptable. Those in the Acura MDX, Honda CR-V, Honda Element, Hyundai Santa Fe, and Kia Sorento improved from their previous ratings of poor to good. Those in the Honda Pilot and Mercedes M class improved from marginal to good. The seat/head restraints in the Toyota Tundra pickup improved to good from acceptable.
In contrast some manufacturers have introduced new models with subpar seat designs. The ones in the BMW X5, Dodge Nitro, and Suzuki XL7 are rated poor. Those in the new Mazda CX-7 and CX-9 are rated marginal.
Among the poor-rated seats in the new evaluations, those in 7 models didn’t make it to the testing stage because the geometry of their head restraints is marginal or poor. This means they can’t be positioned to protect many taller people, so the Institute doesn’t test them. Among these lowest rated seats are those in the Cadillac SRX SUV, Nissan Quest minivan, and Ford Ranger pickup.
What is driving changes?
Safety ratings and government rules are driving the changes. Some manufacturers are making changes to the seat/head restraint designs in their vehicles to earn the Institute’s TOP SAFETY PICK award.
Other improvements are being spurred by changes to federal safety rules. Front-seat head restraints will have to extend higher and fit closer to the backs of people’s heads under a rule issued by the National Highway Traffic Safety Administration in 2004. Originally set to go into effect for front-seat head restraints in September 2008, the agency recently delayed the effective date in response to petitions for reconsideration
Under the new phase-in schedule, manufacturers must start to fit better front-seat head restraints in 80 percent of their models beginning in September 2009. Front-seat head restraints in all new vehicles made after September 2010 must comply.
“There’s lots of room for improvement in the designs of seats and head restraints,” Zuby says. “We know many manufacturers are trying to fit better head restraints in their vehicles, and some have been working with us to boost their ratings as they introduce new models.
“Some manufacturers were waiting for resolution of regulatory issues before fitting better designs in their vehicles. And some didn’t get changes made in time for the Institute’s tests. For example, BMW plans to redesign the seats in the X5 and X3 SUVs to earn better ratings for the 2008 model year.”