Mk 4s on the Midland
Why cascaded coaches might not be the answer to stock shortage
RECENT discussions about impending longdistance train shortages on the Midland Main Line ( RAIL 848) commonly refer to the reuse of Mk 4 coaches that will soon be mostly withdrawn from the East Coast Main Line.
Indeed, Clive Betts (Labour MP for Sheffield East) made specific reference to these sets being hauled by High Speed Train power cars, in a Parliamentary question to the Secretary of State for Transport on March 1 ( RAIL 848).
Even if the reduction in capacity stemming from the increased weight of the Mk 4 over its predecessor is put to one side, this solution could be a non-starter. The Mk 4 coach is not currently gauge-cleared on the MML, and contrary to the implication of Betts’ question, their introduction might therefore be a lengthy and expensive process.
The Mk 4 coach is a little fatter at the step than the Mk 3 coach, and requires greater clearances through curves thanks to the effects of bodythrow (a geometrical effect where vehicle ends throw to the outside and the vehicle centre throws to the inside of a curve). The new CAF Mk 5s behave similarly, being fractionally shorter but slightly wider than the old Mk 3/4 stock.
Platforms present the most challenging interface for gauge clearance, because of the conflict between maximising the structure clearances for trains passing at speed and minimising the stepping distances for passengers.
The challenge is exacerbated as the curvature of a platform increases. And with the Midland Main Line having many more curved platforms than the East Coast Main Line, this challenge becomes a considerable problem.
The MML already runs many of its platforms “foul” - that is, with theoretical negative structure clearances. This is a tolerable risk when using existing stock that has well understood behaviour on a given route, but as soon as you introduce new stock, any subsequent corrective works would have to eliminate “fouls” to both existing and proposed vehicles. This gets expensive!
Having recently undertaken a gauge clearance assessment on the southern end of the MML, it is likely that major modifications (coping stone adjustments and at least a partial reconstruction of the platform wall) would be required at 12 platforms. Less substantial adjustments to the coping stones would probably be required at a further 22 platforms. There are 62 platforms between St Pancras and Bedford stations.
These days, it is not unreasonable to assume £2 million for major platform works and upwards of £0.5m for minor works. Roughly, this gives a £35m price tag to gauge-clear the Mk 4s, and that’s before we begin to look at platforms through Wellingborough and north towards Sheffield. Undertaking this volume of works simply isn’t realistic before the Mk 3 coaches disappear in 2020, especially considering the recent collapse of the East Midlands CP5 framework holder ( RAIL 845).
Prior to the introduction of the Hitachi Intercity Express Programme trains on the ECML, extensive works were required at platforms in stations such as Newcastle, Durham and York (some are still ongoing). Similar alterations to MML infrastructure will be necessary, prior to the introduction of the bimode trains in 2022.
The Class 80x family is longer but narrower than the legacy rolling stock it replaces, and is therefore a little more “gauge friendly”. The difference in scale in introducing this stock to the MML, as opposed to transferring over the ECML Mk 4s, will be significant.
So, to answer Clive Betts’ question in lieu of a clear response from the Secretary of State for Transport: no, I doubt that the MML will be getting cast-offs from the ECML.
This only leaves the current fleet of Class 222s operating long-distance services between 2019 and 2022. Unless another solution is identified, the new East Midlands franchise will still be short of a train fleet when it commences operations at the end of 2019.
Gareth Dennis is an engineer and writer, specialising in railway systems. As well as roles in engineering consultancy, he leads the local section of his professional institution and is a lecturer in track systems at the National College for High Speed Rail. Follow him on Twitter: @garethdennis
“Platforms present the most challenging interface for gauge clearance, because of the conflict between maximising the structure clearances for trains passing at speed and minimising the stepping distances for passengers.”