Challenging conventional approaches to line speed improvement projects - Gareth Dennis

[@johnkeepin7527]

Another retired signal engineer here. The relationship between rolling stock performance, the ability of the system to control it, and the design of a layout is more complex than some think. However, a few historical notes might be of interest. As the 1976-78 project is shown here, part of that was the design of the new 125 mph stock - both the power to weight ratio, or it’s acceleration capability, and it’s enhanced braking, which, more or less, made it capable of stopping from 125 in the same distance as locomotive hauled stock running at 100 mph. Thus there was less signalling work required to cope with the enhanced speed. Another part of it was modernising the signalling set up so that the new stock could actually achieve the designed speed at certain junctions, e.g. there is a 70 mph turnout at Wootton Bassett junction from a 125 mph route. To make it possible to do that, a revised aspect sequence was introduced, to allow the driver to run at the required speed at that location. No point in slowing things down too much having invested in a turnout that could cope with a given speed. With mixed traffic there is a built in conflict of interest between freight operation and higher speed and/or frequent stopping services. In some areas, there are many more stations than there used to be, which would not work with the historic level of heavy freight, unless the latter was restricted to night only etc. Some doubling has taken place in the past to cope better with mixed traffic. E.g. the GW main line acquired doubling from 2 to 4 between Challow and Wantage Rd, to cope with coal traffic from Avonmouth Docks to Didcot A power station (it used to use Nottingham coal via Oxford until the 1985/6 strike). Then another major technique is to avoid flat junctions - e.g. the old flat junction to the west of Reading station was a flat one, but is now a grade separated one, to reduce the conflict between different routes. Sometimes one major project is the top dog. E.g. the construction of the Heathrow Airport branch, which had a requirement to operate a service every 15 minutes. In between those, everything else on the Main Line had to be fitted in, with consequent P Way and signalling requirements to achieve it (more or less). The new stock for Heathrow was electric, but limited to 100 mph, so lots of sums were done to maximise the number of 125 mph services could be squeezed in without displaying unwanted signals behind the quarter hour services. There was a brief discussion about the use of in-cab signalling for higher speeds c.f. lineside. The significant issue with that is the need for human reaction time using outside line side signals plus visibility of them all to interface with it. All the greater than 125 mph lines globally use in cab displays with any kind of manual control.

[@malcolmsmith6615]

This is brilliant, I’m so sorry I was unable to attend on the day. For the first time ever in my career I’ve met someone who understands all of this; I absolutely agree with, and support, everything that was said. Being an ETCS scheme designer I also know about all the misunderstandings around headway improvements resulting from deploying this system. I MUST do my best to attend future talks. Brilliant! Malcolm Smith, Signal Engineer (retired).

[@BCrossing]

Good stuff. Would be interesting to see just how much more expensive maintaining 100mph track is, compared to old 65, 60, or 50mph track

[@dasy2k1]

Another huge constraint of 140mph is that we would need to close every single level crossing on that section.... Including UWCs FPCs etc

[@manomaylr]

Which would make little difference. Surviving a hit by a train at 125 is nigh-on impossible anyway - 140 would not drastically increase the risk associated with level crossings. Closure of crossings should happen anyway, whether the line speed is 125 or 140.

[@BirdStephenJohn]

Journey Time improvement must consider that rail is only part of any passengers journey. HS2 dumping people in Leeds 1/2 hour quicker only to wait 30mins for a local service? Where as calling at Wakefield and Bradford enables quick transfer to bus to final destination or a car.

[@GarethDennisTV]

I mean, yes and no. The point of HS2 is, or at least was, to free up space in e.g. Leeds for more local services to run, which in turn would bring down generalised journey times (the fancy name for what you are describing) for both local and longer distance journeys.