When a car shopper asks for a list of "must – have" safety features, I always mention air conditioning. That usually gets a chuckle.

How is an air-conditioner a safety feature? Simple. Half the people killed in rollover accidents were ejected — often through an open window. When windows are kept closed, occupants have a better chance of staying inside the vehicle, and survival rates go up considerably. But you can’t expect people to keep windows closed if the car doesn’t have an effective air conditioner.

What about seat belts? Don’t they keep people in the car? Less often than you might think. In fact, seat belts fail to do their job in about 20% of the rollover accidents. Even when they do prevent ejection, occupants are better off with the windows closed. When the windows are open, arms tend to dangle out and get crushed between the rolling vehicle and the pavement. Heads can hit the pavement too, causing catastrophic or fatal injuries.

Now the National Highway Traffic Safety Administration has weighed in. NHTSA isn’t quite mandating air conditioning. But beginning in 2013, manufacturers must take steps to keep occupants and their body parts inside the vehicle when the vehicle rolls over.  Even when the windows are open.  NHTSA is leaving it to the manufacturers to figure out how to accomplish this objective.  But it expects that manufacturers will use new side curtain airbags that will completely cover the window openings.

When that happens, air conditioning will be a safety feature no more.

The new NHTSA rule is here.