I primarily race Mini-Z, where reverse is allowed. It takes a lot of discipline NOT to cause accidents by reversing into traffic. If everyone is a high-level driver with good sportsmanship, it's not a problem. I've seen many novice and intermediate races where it is almost impossible to not get taken out since they will reverse into traffic instead of waiting. One car bounces all over the lanes in forward and reverse making it appear as if there are 10... We call it "ninja magic" and anyone who has ever played old school Shinobi will know what I'm talking about.