PHILIPE
Veteran Member
I would define mainline as routes that have medium to long distance trains. So, the line along the north shore of the Severn estuary I would class as a mainline as it carries services between Cardiff and Nottingham and would be carrying passengers who could well making longer journeys - such as Swansea to Newcastle. Branch lines, on the other hand, would be for shorter journeys - usually within local areas, such as the Valley lines in south Wales or the Truro to Falmouth service. These lines do not carry long/ medium distance trains.
In the case of the Exeter to Newton Abbot stoppers, these are operating on a main line but over a relatively short distance. In the case of the Cheltenham/Gloucester ATW services with Pacers, these are travelling 60 miles or so to reach Cardiff with some going even further west. Clearly, one of the most unacceptable journeys to be made by Pacers!
There is a diagram (SX) which involves a Pacer working between Maesteg and Cheltenham all day.