The other is a long disused chord at Tuxford. This would link east to north from the NR test track. Whilst it would be a short chord to put in, the test track doesn't really go anywhere useful and it'd take much, much longer to go Nottingham - Mansfield - Shirebrook - Tuxford - ECML than any existing route I think.
Jason
Its not so much linespeed thats the problem, but the single tracked bit from nottingham to hucknall ( or at least a big chunk of the way, means that the line is pretty much running at capacity with 4 trains an hour. So putting XC 170's or EMT meridians/HST's becomes a bit awkward. I suppose if the robin hood extension was carried out there could be a case to try and get another line from hucknall to nottingham. Then use some creatve signaling to allow the 'fasts' to pass the slows on some overtaking tracks. (there are some areas with lots of space where there used to be freight sidings.)
After all this there is still the problem that significant linespeed upgrades would be required to run the route in any reasonable time (i calculate in a sprinter it would take about anhour, maybe a minimum of half an hour on a high speed service, either a non-stopping 170, or EMT train)
I suppose if you consider it without the robin hood extension, then the Shirebrook - Tuxford line could be a fast non stop section (anyone know the linespeed on there? if its used as a test track it could actually be pretty high) However there may be less of a case for line redoubling near around nottingham.
Maybe going Nottingham - Langley Mill - Kirkby - Mansfield - Tuxford could be faster looking at it? Although I think modifying the platforms at Mansfield woodhouse might be reduce the interference from sprinters, Turn the bay platform into a through one, and then the platform two can be Bi-directionally signal led and the fasts run through there. (mansfield Woodhouse is a bottleneck as the the trains to/from worksop are both there at the same time. With some clever timing I think it could be done so that if we had a 1TPH frequency, the train to nottingham could overtake at Woodhouse, and the train from nottingham could be timed to be sufficiently far behind the worksop train that it wouldnt need to overtake .
I hate to put this idea down, I would love to see More trains on my local line, Unfortunately I can see many problems. Although the Increased ECML linespeed could make up for the slow robin hood line speed, I think the amount of work required compared to speed upgrades in other places would mean it wouldnt get through a cost-benefit analysis very well
End of my lecture, please feel free to ask me to elaborate on anything you are confused about
EDIT Doing a little maths, the time from Kirkby to shirebrook is 19 mins in a sprinter, so a 'fast' service might be able to do that and the line from Langley to kirkby in 20 mins. Then from Newark northgate to Leeds takes 1hr 1min direct. so if we assume that Shirebrook - Tuxford takes about half an hour, and Newark tuxford around 10 mins. That gives 20 + 50+30 = 1hr 40 mins. However the Leeds - London service takes 2h 9 mins to get to Leicester, and from Langley mill to Leicester takes around 25 mins. So overall this gives a roughly similar journey time. yet misses out some of the large cities that EMT's leeds london service calls at.