What you need to know

Highway overpasses are one of the most dangerous places you can be during a tornado. Despite a persistent myth that they offer protection, overpasses actually create a wind tunnel effect that concentrates and accelerates tornado winds. Multiple fatalities during the May 3, 1999 Oklahoma tornado outbreak occurred when people sheltered under overpasses—a tragedy that meteorologists and emergency managers have worked for decades to prevent from repeating.

If you're driving when a tornado warning is issued, your best option is to drive away from the storm's path if you can see it clearly and have an escape route. If that's not possible, abandon your vehicle and lie flat in a ditch or low-lying area, covering your head with your hands.

The deadly myth: how it started

The overpass myth took root after a May 1991 tornado near Oklahoma City. A news crew filming from under an overpass survived, and the dramatic footage aired repeatedly on television. Viewers saw the crew huddled against the overpass girders as the tornado passed, and many concluded that overpasses were safe shelter.

What the footage didn't show was context. That tornado was relatively weak, passed near but not directly over the overpass, and the crew was extraordinarily lucky. The National Weather Service and Storm Prediction Center have since worked to correct this misconception, but the myth persists—often with fatal consequences.

May 3, 1999: when the myth turned deadly

On May 3, 1999, a catastrophic tornado outbreak struck central Oklahoma. The Oklahoma City metro area was hit by an F5 tornado—the most violent rating on the Fujita scale in use at the time—with wind speeds estimated over 300 mph in some areas.

As the tornado bore down on the metro, dozens of motorists fled north on Interstate 35 and other highways. Many remembered the 1991 footage and sought shelter under overpasses, believing the structures would protect them.

They were wrong.

The wind tunnel effect

Rather than providing shelter, highway overpasses create a wind tunnel. As tornado winds encounter the narrow gap beneath the overpass, basic physics takes over: the same volume of air is forced through a smaller space, which accelerates the wind speed. This is the Venturi effect, the same principle that makes wind howl through a canyon or a partially open window.

During the May 3, 1999 outbreak, multiple people sheltering under overpasses were killed or seriously injured. According to the National Weather Service, the overpass structure itself became a debris trap, with vehicles, road signs, and other projectiles funneled directly into the space where people huddled. Some victims were blown out from under the overpass entirely. Others were struck by debris traveling at lethal speeds.

The NWS Norman office documented these fatalities in post-storm surveys and has used them as case studies ever since. The message is unambiguous: overpasses do not protect you. They kill you.

Why overpasses are more dangerous than open ground

Beyond the wind tunnel effect, overpasses present several additional hazards:

  • Debris concentration. Tornado debris doesn't just blow past an overpass—it funnels into the narrow space beneath it, creating a gauntlet of projectiles.
  • No secure anchor. Unlike a basement or interior room, an overpass offers nothing to hold onto. Tornado winds can and will pull you out.
  • Traffic hazard. Stopping under an overpass blocks the roadway for other drivers trying to escape, creating a multi-vehicle pileup in the path of the tornado.
  • Elevation risk. Overpasses are elevated above the surrounding terrain, placing you higher in the wind field rather than lower.

A 2013 study published by researchers at the University of Oklahoma used computational fluid dynamics to model wind flow around highway overpasses during tornadoes. The results confirmed what meteorologists had long warned: wind speeds beneath an overpass can be 20-30% higher than in the open due to the constriction effect.

What to do instead if you're caught driving

If a tornado warning is issued while you're on the road, you have limited options—none of them ideal, but some far better than others.

Option 1: Drive perpendicular to the storm's path

If you can see the tornado and it's far enough away, drive at a right angle to its movement. Tornadoes typically move northeast at 30-40 mph, though they can be erratic. If the tornado appears to be staying in the same spot relative to your position, it's likely moving toward you—drive away immediately.

Do not try to outrun a tornado by driving in the same direction it's moving. You will lose.

Option 2: Seek sturdy shelter

If you're near a town, get to a sturdy building. Go to the lowest floor, an interior room or hallway, and put as many walls as possible between you and the outside. A gas station, restaurant, or even a large retail store is far safer than your vehicle.

Avoid wide-span structures like warehouses, gymnasiums, or big-box stores if you have any alternative—their roofs are prone to collapse.

Option 3: Abandon your vehicle and lie flat in a ditch

If no shelter is available and you cannot drive away, this is your last resort. Leave your vehicle, move away from it (vehicles become deadly projectiles), and lie flat in the lowest spot you can find—a ditch, culvert, or depression. Cover your head and neck with your hands.

This is not safe. You are exposed to debris and the full force of the wind. But you are lower than the surrounding terrain, and you are not trapped inside a vehicle that can be thrown hundreds of feet.

Do not stay in your vehicle. Cars and trucks offer no protection from tornadoes. They are rolled, crushed, and thrown. Seatbelts and airbags are designed for collisions, not 200-mph winds and multi-ton debris impacts.

The role of mobile homes and vehicles in tornado fatalities

According to NOAA's Storm Prediction Center, more than half of all tornado fatalities occur in mobile homes or vehicles. This statistic has remained consistent for decades, even as overall tornado death tolls have declined due to better warnings and public awareness.

Mobile homes are particularly vulnerable because they lack the structural anchoring of permanent homes and are easily destroyed even by weak tornadoes. Vehicles, as noted, provide no meaningful protection and can become projectiles themselves.

The common thread: both mobile homes and vehicles give occupants a false sense of security. People believe four walls and a roof—any walls, any roof—are better than being outside. In a tornado, that's not always true.

Nighttime tornadoes and the warning problem

The overpass myth is especially dangerous during nighttime tornadoes, when visibility is near zero and drivers have no way to see the storm approaching. You cannot visually assess whether you can outrun a tornado if you can't see it.

Nighttime tornadoes are disproportionately deadly. A 2008 peer-reviewed study in Weather and Forecasting found that nocturnal tornadoes are more than twice as likely to result in fatalities compared to daytime tornadoes, even when controlling for intensity. The reasons are straightforward: people are asleep, warnings are missed, and visibility is nil.

If you're driving at night and a tornado warning is issued for your location, do not assume you'll see or hear the tornado in time to react. Get off the road and into a building immediately if possible.

Third-party weather apps are silenced by Do Not Disturb on most smartphones, though Wireless Emergency Alerts (WEA) for tornado warnings still break through on most phones by default. If you're traveling overnight through tornado-prone areas, ensure your phone's volume is up and WEA is enabled in settings.

What meteorologists want you to know

Every spring, National Weather Service offices across the Plains and Southeast repeat the same message: overpasses are not tornado shelters. They issue graphics, videos, and social media posts. They visit schools and community groups. They cite the 1999 fatalities.

And yet the myth persists, often passed from parent to child or shared in viral social media posts that recycle the 1991 footage without context.

If you take one thing from this article, let it be this: if you are driving and a tornado is approaching, an overpass is not your friend. It is a wind tunnel, a debris funnel, and a traffic chokepoint. It will not save you.

Your best chance is to get out of the path entirely, get into a real building, or—if no other option exists—get low, get out of your vehicle, and get as far from the road as possible.

The bottom line

The highway overpass myth has been debunked for more than two decades, but it still costs lives. Overpasses concentrate wind, funnel debris, and offer no secure shelter. The May 3, 1999 Oklahoma outbreak proved this in the most tragic way possible.

If you're caught driving during a tornado warning, drive away from the storm if you can, seek a sturdy building if one is nearby, or abandon your vehicle and lie flat in a ditch as a last resort. Never, under any circumstances, stop under an overpass.

Your life may depend on remembering that when it matters most.

VORTEX is a free web app at vortexintel.app that monitors severe weather nationwide. Pro ($4.99/month) places phone calls to your phone when a tornado or flash flood warning is issued for a location you care about — calls can ring through Do Not Disturb once you enable Emergency Bypass for the number, unlike most third-party app notifications.