Several hundred cars have been fitted with the technology which is a type of WiFi. For the technology to work, both cars involved have to be fitted with devices which then interact with eachother.
Up to now, automotive anti-collision safety devices have relied on sensors and radar. The Michigan trial is a new apporach which is being funded by the US government to the tune of $25m.
The cars have been provided for the Michigan trials, which will last for a year, by Volkswagen Ford, Nissan, Toyota, Hyundai, Honda, Mercedes