Today I used the park and ride from the portway. Got to say I was really impressed. Plenty of parking space got on the bus at 7pm (last bus, they start at 20 to six) then at the ground at 19:20. Bus was waiting to leave at 10 pm back at 20 past in the park an ride. There is an earlier bus if you can get to the Robins at quarter to 10 but that means leaving 5 mins early. Cost £4 but normally pay £7 to park in the trading set if I can get there or it's dry £5 to park at the cricket ground. So to the ones travelling up from Exeter / Dorchester it could be easier for you trying to get through the traffic around Ashton Gate.