I usually come in by train and get the shuttle bus to and from Abergavenny, allowing 90 minutes as recommended. It usually works a treat. I was last at GM 2 years ago, and the bus was caught in unusually bad traffic, meaning it took more than 90 minutes and I missed my train by a few minutes. I think this was down to one-off roadworks, but wasn't sure.
Was it okay last year?