In this paper, we propose the concept of a slowdown warning system in automobiles. If a driver on a highway decelerates suddenly or progresses abnormally slowly (thereby posing a hazard to the vehicles behind him), then, with such a system, all the cars behind him are provided information of this, near simultaneously. This advance information gives the drivers additional time to react; in anticipation of an impending slowdown, and this helps to alleviate collisions. Furthermore, it is seen that even if only a fraction of the cars in a platoon are equipped with such a system, this can still be sufficient to alleviate crashes even in the unequipped cars. This partial equipage also has the ability to considerably weaken (and often altogether eliminate) the shock waves that would otherwise have occurred. A prototype of such a system has been developed and road tests have demonstrated the system's performance to be satisfactory.