Today: How do locked doors help during a crash?

Dear Car Talk

Dear Car Talk | Sep 01, 2011

Dear Tom and Ray:

I observed in a recent VW commercial that the car has a feature that automatically unlocks the doors at the time of a collision. I was always taught that locked doors make the car structurally stronger. Why would a manufacturer create this feature to unlock the doors at the time of a crash?

-- Mike

RAY: It's a good question, Mike.

TOM: Locked doors don't make a car structurally stronger, but CLOSED doors do. And locking the doors makes them more likely to stay closed in a crash.

RAY: The federal government has set safety standards for door latches that are quite strict. So doors almost never open anymore due to the force of the crash itself.

TOM: But the one weak link is the door handle and the rods that it connects to. If your car is moving very fast at the time of a crash, the inertia can move that handle or the rods it attaches to in the door, and that can unlatch the door -- as if you'd pulled the handle.

RAY: But if a door is locked, the handle becomes inoperative. You can pull on it or push on it, but it's detached from the rods that activate the latch, and the door won't open.

TOM: That's why it's recommended that you keep your doors locked when you're driving. And why many cars automatically lock the doors when you start driving.

RAY: VW's crash-response system is designed to shut off the ignition switch, cut the fuel-pump relay, turn on the hazard lights and unlock the doors. And all this stuff is activated the moment the air bag and seat-belt pretensioners deploy -- which is during an accident.

TOM: I'm guessing that VW's thinking is that if you're in a serious accident, it's best to have the doors unlocked so that emergency personnel can have quick access to you.

RAY: But in doing so, it seems that it may be increasing the chances, at least slightly, of unlocked doors flying open during the latter part of a collision, which weakens the protection the car provides and makes it possible for you to fall out if you're not properly belted.

TOM: It would make more sense for VW to program in a delay, so that the doors unlock a few seconds later, presumably after the vehicle has come to a complete stop. After all, first responders are fast. But they're not that fast.

RAY: So we'll suggest it to VW, Mike. In fact, you're joining us in suggesting it to them right now.

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