The Bristol–Bath Railway Path is possibly Britain’s finest urban bike route and certainly Bristol’s. It’s flat, uninterrupted tarmac (save the very occasional road crossing) all the way to the ring road, from where it makes its way to Temple Meads and the city centre on small roads and cycle paths. The route is genuinely very busy throughout the day, but particularly at commuter times: take care and watch your speed.
The path is easily accessible from places like Staple Hill and Fishponds via the road network. There are also a few dedicated cycleway links, notably from Mangotsfield.