I saw it in the early 80's but have never seen it since and all I remember is this scene. Single woman driving down a mountain road at night when a souped up chevelle (or similar) races up behind her and starts ramming into her car and then proceeds to push her right off a cliff. I think the plot of the movie (or show) was that they had to find out who kept pushing people off the cliff. Either a movie or it was an episode of some 70's cop show. Ring any bells?