A driver moves along in traffic, the forward view blocked by a truck or a bend in the road.
 Suddenly, up ahead, someone slams on the brake. Tires screech.
 There is little time to react.
 Researchers here are working to add time to that equation. They envision a not-too-distant future in which vehicles are in constant, harmonious communication with one another and their surroundings, instantly warning drivers of unseen dangers.