See Case 966 re CCing on the G&S.
http://www.waterways-ombudsman.org/publications/case-summaries/2017-18-case-summaries/
Living where we do if we use the car we have to cross at least one of the bridges, I can only think of 2 of the 18 with 2 way traffic, REA bridge that Dora used as an example is no way 2 way (except for pushbikes). The 2 which are 2 way are the only lift bridges, the rest are swing bridges, all manned at this time of year, some handraulic, some powered.
The only parking which I can think of which is "unchecked" and used regularly by boaters long term is roadside N of Parkend Bridge.