Overpasses have long been considered safe havens for people fleeing twisters.
The warning comes as forecasters predict anticipate another violent season. Already this year, there have been 60 tornadoes and 18 deaths.
Taking refuge under overpasses is dangerous, experts say, because tornadoes accelerate 25 percent when funneled through a bridge.
Also dangerous, no matter where a person hides, is the debris tornadoes kick up, which is potentially deadly to anyone not in an enclosed shelter.
"Ordinary, little, small objects become very dangerous when they're getting thrown around at 250 miles an hour," the National Severe Storm Lab's Harold Brooks told CBS News.
Last year, a Kansas television crew shot footage as they hid under an overpass with several others, including children, while a funnel cloud approached.
They made it. Scientists say they were lucky.
Some of the 40 victims of the monster tornadoes that hit Oklahoma City last spring were hiding under highway overpasses.
A few had even left the safety of their homes to hide under bridges.
Remembered Brooks, "There were horribly disfiguring injuries -- people who are scarred physically and emotionally for life."
"I couldn't fathom being in that location," he said.
Stuart Earnest is one who made it. He survived by hiding on an overpass ledge, but a woman nearby was swept to her death.
"The winds had to be over 300 miles an hour under this bridge," Earnest said. "I've never stuck my face so hard into concrete as I did that day. It's incredible what you will do to survive."