Cars that can talk to each other and almost drive themselves at freeway speeds are just two years away from the showroom, according to General Motors executives. The company announced Sunday that the semi-autonomous system for freeways will be an option on an unidentified new 2017 Cadillac model that goes on sale in the summer of 2016. In addition, the 2017 Cadillac CTS will be equipped with radio transmitters and receivers that will let it communicate with other cars, sharing data such as location, speed and whether the driver is applying the brakes. The announcements were made Sunday at the opening of the Intelligent Transportation Society World Congress being held in Detroit this week. They are part of a barrage of similar declarations that are expected from other companies throughout the week as the industry shows off progress toward self-driving and safer cars.