I don't really think the "no reverse" rule is there to protect oncoming traffic nearly as much as it being a form of penalty for making a mistake. The time it takes to make a quick reverse correction and space occupied on the track is typically far less risk than having a marshal block the lane of traffic and further increase the risk of more cars getting tangled with the marshal, see this happen ALL the time. Then you also have some overly cautious marshals that will wait until every car has passed and then eventually get to a car (effectively increasing the time penalty for the mistake)... seen this many times where one of the top qual cars stuffs it into a pipe and goes from first to last.... and sometimes I've seen a car blip the throttle into the pipe to get their car to "bounce off the wall"... this is effectively using reverse and not typically called out during a race... go figure?