The tarka line would be a great route in tsw6 because of its nature and it has a great connection from towns and villages to the city of Exeter. this would be a great hop at Exeter St David's. Also, one of the trains in the Riviera line is on this route making it easier to make as there is only one other train in the route. the route is an hour long and has some great scenery. It is also a great opportunity to add another route with a lot of history. I hope this is enough information if not please reply saying so and I will add more information.
are you referring to this line the one that captain slow from Top Gear made a 10 mile 16 km model railway