The Ford Explorer caused the most damage to the test car

In this story:

• Key is 'basic geometry'
• Light truck market booming
• Ford says weight is key factor
• Related sites and stories

WINDSOR, Ontario (CNN) -- A government study has found that occupants of small cars are at risk when they have a side-impact collision with minivans, pickups or sport utility vehicles.

But it also found that size, weight and structural differences make it difficult to say conclusively that the bigger the vehicle is, the more damage there will be.

"If you take two vehicles the same weight, there's sometimes twice as much damage done by one than the other," says Dr. Ricardo Martinez, director of the National Highway Traffic Safety Administration (NHTSA). "That means there are other issues besides the basic weight."

Martinez, who is attending an international vehicle safety conference in Windsor, Ontario, calls such issues "basic geometry."

CNN's Ed Garsten looks at the results of the crash tests 2 min. VXtreme video

Watch the crash tests 1.5MB/27 sec./240x180 1 MB/27 sec./160x120 QuickTime movie

"While LTVs (light truck vehicles) account for about one-third of all registered vehicles," the NHTSA study says, "they are involved in half of all fatalities in crashes with passenger cars."

About 42,000 people die each year in traffic accidents in the United States.

The so-called "compatibility tests" conducted by the NHTSA were designed to measure how much damage the heavier and higher-riding light trucks do when they are involved in crashes with a small car.

There has been considerable interest in the tests because of the boom in sport utilities.

A Chevrolet S-10 crash test

The light truck segment of the market has been on the rise -- it represents 47 percent of all light vehicle sales so far this year -- and safety advocates have begun to call for design changes to make them less damaging to cars.

NHTSA conducted the tests in March at its car safety research facility in East Liberty, Ohio.

They involved ramming 1997 Honda Accord sedans with a 1997 Ford Explorer sport utility, a 1997 Dodge Caravan minivan, a 1998 Chevrolet S-10 compact pickup and a 1997 Chevrolet Lumina mid-sized car.

The research included a series of eight crash tests, all of which were designed to reproduce a typical intersection crash where the striking vehicle was traveling at 30 mph, and the struck vehicle, taking a side impact, was traveling at 15 mph.

The Explorer caused the greatest damage and had the highest probability of causing injury to a passenger. But the Chevrolet S10 pickup, another large vehicle, was found to be the least likely to cause injury. The Lumina, the vehicle with the least mass, fell in the middle.

The tests also indicated that none of the crash test dummies would have "died" from injuries sustained during the impacts.

Ford, which has performed its own tests by crashing vehicles into its Taurus, takes issue with the results.

"The test we ran would say that weight is perhaps the most important factor," says Ford spokeswoman Helen Petrauskas.

Nevertheless, the results may quiet those who claim that sport utility vehicles are a "danger" to those in smaller vehicles.

"This is not a car-truck compatibility question," says Bob Lange of General Motors, "but a vehicle-to-vehicle compatibility question."

GM's top safety engineer said last month that more lives could be saved by improving the side-impact resistance of cars than by lowering the height of truck bumpers.

The NHTSA findings are only preliminary, and it plans to carry out full front-impact crash tests and work with computer models before it has what it believes will be conclusive results.

In the meanwhile, it is asking automakers to look into improving the design of both large and small vehicles.