Four decades after a failed push to outfit cars and light trucks with devices that force drivers to buckle up, regulators and the auto industry are giving interlocks another chance.
The U.S. government tried to mandate ignition interlocks — which prevent a vehicle from starting unless seat belts are fastened — in cars in the early 1970s to prod more people to use seat belts. The rules prompted such a public outcry that Congress made it illegal for regulators to require the interlocks.
A transportation bill that Congress passed in 2012 lifted some of the restrictions.
Now car companies are asking the National Highway Traffic Safety Administration to let them use interlocks in lieu of crash tests for people who do not wear seat belts.
NHTSA says it sees the promise of these interlocks, but is not yet ready to give automakers the green light.
In a regulatory notice that denied a petition from BMW to offer interlocks, the agency said it will study interlocks through 2015 to figure out whether they will save lives by making people buckle up.
“The agency agrees with the theoretical premise that a seat belt interlock system could have the potential to increase seat belt use rates,” the notice says. “This is consistent with our past research. However, the degree to which seat belt use will increase is not clear.”
In its October 2012 petition, BMW said that being free of the unbelted crash test would help the company develop lighter and more spacious cars.
The petition from BMW is an early sign of a shift occurring as airbags, high-strength frames and active safety features do a better job of keeping people out of deadly crashes. To make cars lighter and more comfortable, automakers are looking to get rid of bulky structures — such as knee bolsters — that used to be more important.
“We’re talking about weight savings for the CO2 and fuel economy constraints that are going to hit us in the next few years,” says Sam Campbell, head of U.S. safety engineering at BMW. “It’s a win-win situation for all aspects of vehicle design.”
BMW and other automakers also want to save on development costs. In Europe, where seat belt use rates are higher than in the United States, regulators do not make automakers test their vehicles with an unbelted crash test dummy.
Campbell said BMW hopes that NHTSA’s findings will lead to changes in federal vehicle safety standards in 2017 or 2018.
One of the big questions for NHTSA and car companies would be how to design interlocks. They can be more stringent, and stop the vehicle from being started at all, or less stringent by stopping the car from being put in drive or going above a certain speed.
In its petition, BMW, which is fine-tuning a prototype, encouraged the third option.
Stopping the driver from starting a car would force someone to use a seat belt even if the driver is idling the engine in a parked car for the air conditioning. BMW says there are other tasks — like driving to a mailbox — that may not require a seat belt.
“A pure interlock?” Campbell rhetorically asked. “Customers would not accept that.”