The U.S. Department of Transportation is proposing to require new cars to communicate with one another. Such communication is a great idea. But that doesn’t mean the federal government should mandate it or that it will prevent all accidents.

Under the rule, manufacturers would have to equip new cars and other “light vehicles” to transmit a “basic safety message” giving other vehicles information “such as (their) heading, speed and location,” said the department’s National Highway Traffic Safety Administration. That would let cars “see” things drivers can’t. They could see through fog, past trucks and around corners – as long as what they’re seeing is transmitting the basic safety message.

The agency hopes cars would alert their drivers to a range of potential risks. For example, your car might warn you not to enter an intersection or make a left turn because a crash would be likely. It could tell you that another vehicle is in your blind spot – especially if you try to change lanes. And it could tell you that someone up ahead is braking quickly.

The technology is exciting. The basic safety message could save lives.

But because cars stay on the roads for years, it will take a long time for the communication devices to be in every (or even almost every) car.

And because the technology allows your car to “see” only other vehicles that are transmitting the basic safety message, relying on it when not all cars have it is dangerous – and the more cars that have it, the more drivers will rely on it. They’ll expect to be alerted when there’s a danger. And so they’ll miss old cars or bikes.

Vehicle-to-vehicle communication could contribute to safety. But it would be expensive and is not without risks of its own.