So the railway east from Saxmundham is going to be completely rebuilt in the next few years. A new temporary line will be built, running close to Leiston Abbey, and the existing line to Sizewell will be temporarily mothballed.
Would it be possible, to, in conjunction with these works, reinstate a passenger train service between Saxmundham and Leiston? Need not be anything more than a 3-car 755.
It would be
possible sure, but very unlikely that it would be worthwhile. It would also need additional trackwork and signalling north of Saxmundham so that both northbound and southbound mainline services could use the same platform, as otherwise there is nowhere to berth the branch line train while the mainline trains come through.
Leiston already has a good bus service, with up to 4 buses an hour to Saxmundham, where passengers can connect with rail services, and a journey time of about 15 minutes.
By the time people have walked to the station on the edge of town, it's unlikely that the train would reduce that time appreciably given the better penetration of the bus services.
Running a 4-mile branch line is a poor use of resources. If you're looking at passengers making onward connections at Saxmundham then you only need to run an hourly service because trains through Saxmundham are only hourly and pass near the station so a single journey would connect with both northbound and southbound trains. That means that you would have the train and crew sitting idle at Leiston for the best part of 45 minutes out of every hour.
The only way it would be viable would be if there was currently unmet demand for additional services between Saxmundham and Ipswich, but
not north to Lowestoft, and the service could run through from Leiston to Ipswich, but that would require redoubling or at least passing loops on the line between Saxmundham and Woodbridg, which at the moment can only sustain an hourly service.
Still bigger than places like Gunnislake though, which have much longer railways to access them. For Leiston it is literally a few miles.
When you look at Gunnislake, Calstock, Bere Alston and Bere Ferrers combined, their total population is about 7k – 7.5k, so bigger than Leiston.
And if that service
wasn't running now and anyone suggested reviving it, they would be laughed out of town.
The reason that that branch line was retained is because road access to several of the villages along the route is very poor, and the geography of the area and the rivers in the way would make it very expensive to improve that road access – it certainly wasn't because those small communities specifically merited a train service.
The short distance to Leiston is actually part of the problem and why it wouldn't be a good idea!