I'm raising a point, and appologise for not answering you question.
Does it really make any difference if it is a one time trip... the straighest point between 2 points is the straightest line possible.
To veer only 6 miles off your route to your destination and to return another 6 miles back to your original straight line route is a gallon or more of fuel... and lost time. It adds up quickly.
Somebody pays everytime you go somewhere on a super highway, city street, or across a wide body of water... taxes, or fees (probably both)... nothing is free.
The 12 mile long bridge from New Brunswick to Prince Edward Island is $45 one way... free the other. Or you can take a ferry... loss of a lot of time and more expensive.
Of course we had a choice... but we wanted to visit Clive and Marne on Prience Edward Island... guess we could have swam.... well floated over.
Dig deep, have a good time, you'll forget the cost.
Sleepy
BTW... would someone really buy a new truck with less capiblilty to get a couple of bucks off a bridge toll?