Well, what I said in the Okehampton thread was that it wouldn’t cost 3 times as much to build a station on an open line than a closed line. But I did say it would cost ‘a little’ more, because the big difference is where you have to do work right next to the track, ie platforms etc. That’s for building new stations. For work on the track, there is a definite saving in longer closures.
In this case, Thanet Parkway is going to have 12 car platforms, which will need closures to build. I’m fairly sure there will need to be some signalling changes too. Perhaps most importantly, it’s a big station the footbridge and lifts (I’m assuming lifts, seems reasonable) will be the thick end of £5m, the car park and highway amendments another £5m at least - which I’m sure will be more effort and cost than all the track renewal on the IoW. There will also be a fair bit of utilities work which is never cheap.
For the IoW, an extended closure will definitely help. To put it in context, whilst I don’t know the detailed scope of the work it doesn’t actually look to be that much, and I guess it could all have been done in a series of weekend blocks, and probably not many at that. A track lowering through a short platform is a day’s work. Installing a short loop (100m?) is two weekends at most. A new short platform - a couple of weekends, and some overnight works for finishing. However this all assumes 24 hour working at weekends. By closing the line it can be Mon - Fri day shift only, with a smaller workforce, which reduces the wage bill.
I suspect the reason for the long block is more to do with the trains and their compatibility with the infrastructure. Clearly with platforms being lifted etc, you couldn’t run the service with the old trains, or the new trains, with the work part done. So you have to programme it such that all the works are done in one go. Then there will be integration and compatibility testing for the new kit, plus all the training. That alone will be several weeks. Once the railway is going to be closed for an extended period, it makes sense to make the work within the closure to be delivered as cost effectively as possible.
So, to answer the original question - in terms of effort (quantity of material, working hours, etc) I’d say there isn’t much difference between the two projects. But there is definitely an efficiency for the IoW in taking the time to build it slowly, mostly in weekday day time hours, compared to Thanet where a decent proportion of the work will have to be when trains aren’t running at weekends.
