A giant experiment begins on the streets of Ann Arbor, Michigan, in a few weeks.
About 2,800 cars, trucks and buses will be communicating.
The data links will warn drivers of potential dangers like stopped traffic, or a car blowing through a red light.
The devices can even get traffic lights to turn green if there are no cars coming the other way.
The $25 million test is being conducted by the U.S. Department of Transportation and the University of Michigan.
Officials say connected cars could be on the road nationwide within a decade.