Living on the south coast, I usually travel to VP by train, but on one of the rare occasions I went by car was an evening cup game against QPR in 2004. A work mate who supported QPR fancied going and preferred to drive, so we parked in the leisure centre. It took over two hours to get out of the car park, and the reason given was that the usual policing of traffic had been reduced because it was a low category game.
Also on that night, and this may be part of the cause or a related symptom of the reduced policing, a steward was killed when fights broke out:
Death of a Steward ... what 'really' happened.
One thing is for sure: if the traffic close to VP is not policed and the temporary one way systems enforced, there will be chaos after the game.