When we went to San Francisco 2 years ago we used the San Francisco Hop On Hop Off system which is a series of open air top deck buses that carry you throughout San Francisco and you can get on and get off as you please, takes in the whole of San Francisco(Google it and see what you think) we left our truck at a free parking lot just on the north west side of the Golden Gate Bridge and a Hop on Hop off station was right across the road. Crossing the Golden Gate on the top deck in the open air is a rush for sure.