SENECA, MO. - More than a third of the 22 people killed by a tornado that smashed parts of Oklahoma and Missouri over the weekend died in cars, troubling experts who say vehicles are one of the worst places to be during a twister.

"It's like taking a handful of Matchbox cars and rolling them across the kitchen floor," said Sgt. Dan Bracker of the Missouri State Highway Patrol, surveying the damage in and around Seneca, near the Oklahoma line, the hardest hit area. "This is devastating."

Among those killed were three people in Oklahoma who were rushing to reach a relative's house in their car; a woman whose car was blown off a road near Seneca; and four family members -- Rick Rountree, his wife, his 13-year-old son, and his mother-in-law -- who were in a van on the way to a wedding when a twister packing winds of 170 mph struck the Seneca area Saturday night.

"They were on the road when the warnings came," said Rountree's brother-in-law, Larry Bilke.

About 100 people have died in U.S. twisters so far this year, the worst toll in a decade, according to the National Weather Service. Tornado season typically peaks in the spring and early summer, then again in the late fall.

This could also prove to be the busiest tornado season on record in the United States, though the final figure on the number of twisters is not yet in.

All together, at least 26 people died in Missouri, Oklahoma, Georgia and Alabama after the severe storms erupted Saturday over the Southern Plains and swept east.

The death toll rose Monday when Tyler Casey, a 21-year-old firefighter in Seneca, died at a hospital. Officials said he got caught in the tornado while trying to warn people to seek shelter.

According to data from the National Weather Service's Storm Prediction Center, 49 of the 705 deaths -- or about 7 percent -- attributed to tornadoes from 1997 to 2007 were people who were in vehicles when the storm struck.

"They can cover more ground than you can in your car, so unless you know you are moving away from the tornado, the best thing you can do is find a strong structure," said National Weather Service meteorologist Andy Foster.

The twister that struck Seneca and surrounding Newton County was moving at 50 mph to 60 mph, Foster said. One car was found a half-mile from the tornado track.

Authorities were still piecing together how some of the other victims died over the weekend. But the Missouri Highway Patrol said one person was killed when her vehicle was blown off the same road where the Rountree family died.

In Picher, Okla., 32 miles away, a man and a woman died when their car was blown into a lagoon. The body of another man from the car wound up in a tree nearby. A 13-year-old girl who was riding in the car was injured.

Fire Chief Jeff Reeves said they were not trying to outrun the twister.

"I think they were actually trying to get to a family member's house on the south side of town to help them, and they just didn't make it over," Reeves said.

Worst place to be

Val Castor, one of the many spotters who bring dramatic video of tornadoes to local TV stations in Oklahoma, said the number of people on the road during tornadoes seems to have increased since 1996, when the movie "Twister," which depicts meteorologists chasing tornadoes, came out.

He said driving during severe weather is extremely dangerous for the inexperienced, because they don't know where a tornado will form or what direction it will go.

"Vehicles of any size really don't fare that well in a tornado. Vehicles can be thrown and tossed by the wind," said Rick Smith, warning coordination meteorologist with the National Weather Service in Oklahoma.

As with mobile homes, the problem with cars is that they are not anchored to the ground, and the wind can easily get underneath them. Smith said winds of less than 100 mph can flip a car.

"That is probably the worst place that you can be when a tornado, or even some of the severe storms that we see in Oklahoma, happen," he said.

Smith said people should avoid driving when severe storms are forecast and should seek shelter in a truck stop, restaurant or other permanent structure if caught on the road. As a last resort, Smith said, motorists should get out and find a low-lying area, such as a culvert or a ditch, where they can duck and cover.