I know the junction your thinking off, and it isn't Adwick. It's between Fitzwilliam and South Elmsall on the Doncaster - Leeds line. In order to build the flyover, a serious amount of earthworks is required because of all the waterways in the area.
Earthworks would be required, but it wouldn't be beyond the realms of possibility. This scheme would be similar in length to the new chord going in North of Nuneaton. Small streams can easily be culverted through, so wouldn't need full bridges. There may be one or two bridges required for footpaths though.
Dore Station Jn is being redoubled anyway soon (or at least that is what's being planned), which will be sufficient for the traffic that currently passes there. There is room available to add a new line from there to Sheffield, but it would mean the lines currently there would have to be re-aligned a little, possibly reducing linespeed.
Doubling Dore Station would be sufficient for the services that pass through it (ie the fasts and slows to Manchester), but this will not have an effect on capacity North of Dore Station (in fact, adding a Manchester service will take up existing spare capacity if anything). The current arrangement also means that trains to Manchester have to cross the MML down line, and the conflict can cause delays in both directions. I would prefer to see the services separated from the MML completely, as that would bring a complete step change in capacity south of Sheffield.
As well as there being enough room, the bridges were designed to take 4 lines on this section. The decks would probably need replacing, but I imagine the abutments and foundations wouldn't, especially if the new bridges were limited by weight to what they were designed for. The linespeed issue I can't comment on (not my area of expertise), but the run is fairly straight as it is, and I can't see it altering too much.
The big capacity killer between Aldwarke Jn and Swinton is the speed differentials, which is 35/90/100HST That needs sorting first before anything else is considered.
Agreed. 4-tracking Aldwarke Jn to Swinton would provide a much longer section where fasts and slows do not conflict (ie not just the Rotherham loop).
The sheer cost of new tunnels and new alignments means that this will never get the go ahead, even though Nunnery Main Line Jn is 1 of, possibly even the biggest pinch point in the North East.
I know that this would be expensive, but the sheer increase in capacity would bring huge benefits. I developed a plan to do this (which I'll dig out later), which would minimise the cost, but it will still be large. For example some of the bridges over the line only carry a dead-end road, and could be removed. However, the signalling for a remodelled throat would be almost as much (if not more) than the earthworks.
Chesterfield station - Clay Cross Jn has been re-modelled a bit recently (I'm talking about 2 or 3 years ago now). Trains to/from the Nottingham direct now use the slow lines (used to be the goods lines) between Clay Cross Jn and Chesterfield. There is now a double ladder immediately after the station so traffic can be segregated easily. The fast lines at Clay Cross Jn were plain lined at the same time.
I know this was recently re-modelled, and I have to admit I don't like what they've done. However I agree that this one in particular is unlikely to come about.
Sorry if I've put a downer on your plans, as they are all good suggestions. Sadly though, they are very unlikely to ever come about.
No worries. It takes more than reality to bring me down! :roll: