Imagine you’re driving up a hill toward a traffic light. The light is still green so you’re tempted to accelerate to make it through the intersection before the light changes. Then, a device in your car receives a signal from the controller mounted on the intersection alerting you that the light will change in two seconds—clearly not enough time to beat the light. You take your foot off the gas pedal and decelerate, saving on fuel. You feel safer, too, knowing you didn’t run a red light and potentially cause a collision in the intersection.