Sport utilities showed modest improvement in rear-crash protection according to a U.S. insurance industry analysis released on Tuesday, but more than half the 87 light trucks tested fell short of optimum safety and pickups fared the worst.

David Zuby, vice president of vehicle research for the U.S.-based Insurance Institute for Highway Safety, said the test results showed there was plenty of room for improvement.

It's not a major feat of engineering to design seats and head restraints that afford good protection in these common crashes Zuby said in a statement.

Neck injuries are the most common reported in auto crashes, accounting for two million insurance claims annually, the group said.

Safety experts say the head and torso must move together to minimize the risk of whiplash. Head restraints must be high enough and close to the back of the head, and seats should meet certain stiffness criteria.

While results for 2004-07 models were mixed overall for the light truck class, Zuby said many foreign and domestic automakers are moving in the right direction on rear-crash safety.

Some manufacturers have made design changes while others are waiting for regulatory issues to be sorted out before moving ahead, he said. Many new SUVs have been updated in the past year while manufacturers have been slower to make improvements in pickups and minivans.

The institute's tests included measuring seat geometry and simulating crashes at 20 miles per hour using a dummy designed to measure neck forces. Performances were rated either poor, marginal, acceptable or good.

In the latest evaluation, seat/head restraint combinations in 17 of 59 SUV models were rated good and five were acceptable. The remaining 37 were marginal or poor. In 2006, only six of 44 SUVs earned good ratings.

In vans, three were rated good and two acceptable -- about half of those tested. In pickups, one model posted a 'good' score, while five were acceptable. The remaining 11 were marginal or poor.

The redesigned 2007 Tundra from Japan's Toyota Motor Corp. was the lone pickup that received a good rating. The 2006 Tundra received an acceptable mark. The improved rating in the 2007 version is a boost for the vehicle that fell short in government tests to assess safety in head-on crashes.

The Tundra is Toyota's answer to big selling full size pickups made by General Motors Corp., Ford Motor Co., and DaimlerChrysler AG's Chrysler Group. The Tundra posted four stars in the National Highway Traffic Safety Administration frontal tests, while its U.S. rivals registered five stars, the highest mark. NHTSA does not perform rear crash tests.

The insurance institute also said that that the CR-V sport utility made by Honda Motor Co. Ltd received a good rating this year compared to a poor score in 2006.

The Ford Edge crossover SUV, introduced in 2007 as a key product in the company's turnaround strategy, posted a good rating in its first rear crash assessment.

(Reporting by John Crawley)