Self-driving cars use GPS, satellite communication, for their navigation. But, as anyone with a satellite radio system in his car knows, there are sometimes brief moments of interruption in the communication. That can be very dangerous for self-driving cars. That’s why researchers are testing an additional communication technology for autonomous cars. They have equipped cars with “vehicle to vehicle communication” allowing the cars to communicate with each other and use data from other devices to see beyond what is immediately in front of them. For instance, if a traffic signal around a blind curve becomes red, the car can sense it and prepare to stop.