Speed is just like a short story I read in the early 1980s

Rating: Null/10 (26 July 2005)

When I was a kid, I had a subscription to Alfred Hitchcock's Mystery Magazine. One of the stories (I forget the title) was about a recently divorced woman who puts the kids in the car and sets off for some undisclosed errand. At one point, the daughter asks her mother, "Are we over 50 miles per hour yet?" When the mother responds "yes," the daughter hands the mother a note from her ex husband, who reveals that there is a bomb in the car which will detonate when the car dips below 50MPH. Running low on gas, the quick thinking mother manages to drive the car onto the beach, and as the tires are spinning in the loose sand, the mother and children dive out of the car just before it explodes.
Doesn't this sound a lot like Speed? Shouldn't somebody be paid a credit for this? Am I the only man in the world who read this story?