Actually that's quite a good point mumrar, one of the main problems on the southern (KGX-PBO) and middle portions (GRA-NCL) is the interaction of 125mph expresses with local or inter-regional services (top speed probaly 100mph or less) and with frieght services as well. One of the reasons that the ECML struggles for capacity is trying to fit all this together in some sort of coherent structure. Imagine throwing in another group of trains all running at 140mph, the impact on available paths would surely be pretty severe.
Yeah, signal sighting distances arent the only obstacle in the way of 140mph running: Youve also got to consider the squeeze on paths that would be caused through having a faster running flight of trains, which is another good reason why 125mph has been stuck with as the maximum. Although if the ECML had gone to 140mph with the introduction of the IC225s, then the long distance HST services, with a maximum speed of 125mph, could be pathed as limited stop services (Such as KX, possibly Newark, Doncaster/York, Newcastle & Edinburgh) while the faster electric services would have a few more stops and so the timings along the route would balance out. In actual fact this is already the case with the Aberdeen and Inverness services, and has been for many years, I suspect since the ECML electric timetable was introduced. Is this a carry over from plans for 140mph running? Although of course, this still completely fails to address the problems caused by sharing tracks with the considerably slower regional, local and freight services on the route.
It wouldnt be possible to use as many HSTs on the shorter runs over mainly electrified routes, or the diagrams entirely over the core electrified ECML, though as they wouldnt be able to keep time with the 140mph IC225 schedules. There would have to have been a larger fleet of 225s, perhaps 35 sets (I doubt that the few minutes saved on schedules would release any additional trains over the actual current requirement), not only to cover more of what are actually HST diagrams, but also to compensate for the higher failure rate that would ensue with day in, day out 140mph running. I wouldnt have fancied the class 91s chances if the ECML had been passed for such speeds.
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I'm guessing the flashing green was done by re-wiring the existing green aspect of the existing signals. I'd expect adding an extra aspect of a different colour would have required replacing the signals altogether, which seeing as BR weren't excatly rolling in money (hence APT and INTERCITY 250 not going ahead) was probablly deemed to expensive. Also, the following post sounds like a good explanation too.
Here's hoping IC225s get moved to GWML so they can make use of ERTMS to hit 140mph (I'm thinking, with the extra 2tph to Bristol TM, the London - Swansea services could go non-stop between Reading and Bristol Parkway, which should give a nice 140mph stretch from just west of Reading to Swindon). Now, of course we have to get wires to Swansea first, but that's another agrument.
The installation of ERTMS doesnt guarantee the introduction of 140mph running. There would still be infrastructure enhancements and alterations required (Although the GWML would probably be one of the easiest routes to apply such changes to), and the planners would still have to consider the additional pathing conflicts that a faster flight of trains would bring. Its just a more advanced form of signalling.
And as far as I know, an initial 140mph capability is not included in the Hitachi IEP specification, with 125mph being the top whack (Although reportedly the design could be adapted for the higher speed). As for 225s going to the GWML, thats just a dream: The GWML already has new IEP trains assigned to it, this is unlikely to change.
