The designs of seats and head restraints in a majority of current US-market SUV, pickup, and minivan models were rated marginal or poor in the latest evaluations of occupant protection in rear-end collisions by the Insurance Institute for Highway Safety.

Those in 21 models were rated good for protecting people in rear impacts, but those in 54 other models scored marginal or poor. Another 12 were rated acceptable.

The testing found that the seat/head restraints in more than half of light truck and minivan models fell short of state-of-the-art protection from neck injury or whiplash.

The ratings of good, acceptable, marginal, or poor for 87 current models were based on geometric measurements of head restraints and simulated crashes that together assessed how well people of different sizes would be protected in a typical rear crash.

Among the best performers were 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 three minivan models from Hyundai and Ford earned good ratings.

The redesigned Texas-built Toyota Tundra was 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," said David Zuby, senior vice president of the Institute's vehicle research centre. "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 2m insurance claims each year in the US, costing at least $8.5bn. Such injuries aren't life-threatening, but they can be painful and debilitating, the institute said.

In the latest evaluations, the seat/head restraint combinations in 17 of 59 SUV models were rated good, five acceptable, 14 marginal, and 23 poor. In minivans, seat/head restraints in three models were rated good, two were acceptable, one was marginal, and five were rated poor. In pickups one was good, five were acceptable, five were marginal, and six were 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 was much better. In 2006 those in only six 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 suggested.

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 sub-par seat designs. The ones in the BMW X5, Dodge Nitro and Suzuki XL7 were rated poor. Those in the new Mazda CX-7 and CX-9 were rated marginal.

Among the poor-rated seats in the new evaluations, those in seven models didn't make it to the testing stage because the geometry of their head restraints was marginal or poor. This meant they couldn't be positioned to protect many taller people, so the Institute didn't test them. Among these lowest rated seats were those in the Cadillac SRX SUV,

The institute said some manufacturers were making changes to the seat/head restraint designs in their vehicles to earn its top safety pick award while other improvements are being spurred by changes to federal safety rules under which front-seat head restraints will have to extend higher and fit closer to the backs of people's heads.

The rule was issued by the National Highway Traffic Safety Administration in 2004 and originally set to go into effect for front-seat head restraints in September 2008, but 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% 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 said.

"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."