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Last night's I-5 bridge collapse in Mount Vernon, Wash., sent two vehicles and three passengers plunging into the Skagit River after a semi truck apparently sideswiped part of the bridge. After crashing into the river, the vehicles appear to have been caught up in the bridge scaffolding, saving them from falling into the water.

Dan Sligh, who was in one of the vehicles, a pickup, said it was a miracle he survived. He was definitely lucky. According to the National Highway and Transportation Administration, about 400 people die every year in the U.S. from drowning in their vehicles. So prepare yourself now.

The good news is that you can escape a sinking vehicle. But you've got to be quick. According to The University of Manitoba's Gordon Giesbrecht, who trains law enforcement officers and others on underwater-vehicle escape, a person has about a minute to get out alive. Here are his five rules of survival—and one caveat.

Rule 1. Don't Call 911 until you're out of the car. You're going to need every second to get out of that vehicle. Worry about calling 911 once you've made it out alive, or, as in the case of the I-5 collapse, if your vehicle isn't submerged. "Time is critical," says Giesbrecht. "If you touch your cell phone you're probably going to die."

Rule 2. Unbuckle.

Rule 3. Don't open the door! Roll down the windows instead. Opening the door is very difficult against the water pressure and it also allows so much water into the vehicle that it will speed up the sinking process.

You'll have 30 seconds to a minute until the water rises to the bottom of the passenger windows. This is what Giesbrecht calls the floating period. After that, the water pressure will force the window against the doorframe, making it essentially impossible to roll down.

Caveat to Rule 3: Break that window. Since most vehicles these days have electronically controlled windows, the circuits probably will short before you have a chance to roll them down. In that case, you'll need a tool to break the window open.

Two of the most popular are the LifeHammer ($14.95), which has a hardened-steel point to help crack open the window, and the ResQMe keychain ($9.95), which uses a spring-loaded mechanism to shatter glass. If you plan on practicing with either one of these, take it from personal experience and wear work gloves. Otherwise you will cut your hands. "Make sure these tools are within reach at all times, otherwise you'll never get to them in time," says Giebeck. "And they won't work underwater. Again, you've got act quickly."

Rule 4. Children first. Everybody should go out their own window if possible, but the kids are going to have a harder time fighting through the rush of water, so push them out if you have to. Greisbeck suggests starting with the oldest kids and taking the youngest out in your arms.

Rule 5. Get out. Swim through the broken window as fast as possible.

If you've failed to get that window rolled down or broken, you'll still have the slightest of chances to escape. Once water fills the car, the pressure will be equalized and you will be able to open the door. But to do this, you will also have to be expert at holding your breath in an extremely stressful situation. Giesbrecht says that unless you're a modern-day Houdini, the odds are pretty slim.

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John Galvin covers natural and man-made disasters for Popular Mechanics. Follow him on Twitter at @JohnPGalvin.

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