"The Long Walk", published under Richard Bachman. According to King it was the first book he ever wrote (per wiki).
There's plans to do a movie of this one too.One hundred teenage boys participate in an annual walking contest called "The Long Walk", which is the "national sport". Each Walker must maintain a speed of at least four miles per hour; if he drops below that speed for 30 seconds, he receives a verbal warning (which can be erased by walking for one hour without being warned). If a Walker with three warnings slows down again, he is "ticketed". The meaning of this term is intentionally kept vague at first, but it soon becomes clear that "buying a ticket" means to be shot dead by soldiers riding in half-tracks along the roadside. Walkers may be shot immediately for certain serious violations, such as trying to leave the road or attacking the half-track. The soldiers use electronic equipment to precisely determine a Walker's speed.