Can't believe you've not driven Coombe before!
The reason for the limited cars on track at once will be NOISE! Remember they are oppereating under a noise abatement order at the moment

flocking council and shitty locals.
Another reason is that people got sick of coombe letting 30-50 cars out in one session, it was like racing on the m25 in rush hour
ANyway, glad you enjoyed it... now get that taxi of yours going!!!!!
Alex