The US National Highway Traffic Safety Administration has proposed a new rule that would require vehicles of 10,000 pounds or less to have larger and stronger side air bags, to prevent passengers from falling out of the side window in rollover crashes.

If the rule is approved, new cars will be required to meet a performance standard that could mean larger and more robust side curtain air bags that cover more of the window opening and remain inflated for longer.

The side air bags will also need to be strong enough to prevent a person from being ejected, even when they are not wearing a seat belt.

The move is expected to save nearly 402 lives a year as rollover crashes claim 6,200 lives every year and leave 5,271 seriously injured.

If the proposal is approved, the phase-in of the new air bags will begin from the 2014 model year and all vehicles will need the air bags by 2017.