|Downhill Street Bicycle runs one bicycle at a time on a paved downhill course. There are about ten curves per mile of the course and a bicycle speed of 30 MPH to 40 MPH. The bicycle runs are timed.|
Basically, people have developed vehicle racing skills by running bicycles down steep streets and turning in to ninety-degree intersecting streets. Then this fundamental is being developed into a paved downhill course design and a timed competitive event.
Here is a link to the Downhill Street Bicycle rule book: