Most regions have courses in the 40-60 second range and try to release a car every 20-30 seconds. This can mean there are as many as 3 or 4 cars on the course at one time, but far enough spaced out that they do not interfere with one another. There will be a series of work stations on the course, each with a red flag. Should someone spin or stop on course, the other cars are also stopped and granted a re-run.