Ackroyd-Stuart to the rescue?

Informed Sources

In the March 2016 column, following a long session with the Great Western Electrification Project (GWEP) team, I included a table of the ‘Hendy Dates’ for the commissioning of the various route sections. The footnote for RS5 Didcot-Wootton Bassett said ‘Solution for Steventon High Street Bridge needed’.

In a letter to stakeholders on 11 September, Network Rail confirmed that the full reconstruction of Steventon bridge will not be possible in time for the start of electric services in December 2018. Apart from the physical work, the eventual demolition and reconstruction of the bridge will be subject to approval of the Listed Building Consent. Obtaining consents has been a major drag on the progress with GWEP.

As I explained, this bridge, just outside Didcot, is adjacent to Stocks Lane level crossing. This means that the overhead contact wire has to go up to its maximum height to clear traffic over the crossing and then fall rapidly to go under the bridge.

In this situation the speed of the train determines the maximum gradient of the contact wire. The rule of thumb is that the maximum gradient is five times the speed in miles per hour.

For 125mph the maximum gradient is thus 1:625. But the proximity of bridge and crossing imposes a gradient of 1:270.

So working backwards and rounding up you get a maximum speed of 60mph. Applying the standards for the braking distance to speed restrictions, plus the time for a train to accelerate back up to linespeed, I estimate the loss of time negotiating what would be a Permanent Speed Restriction at around two minutes.


Given that electrification and the new Hitachi Class 800 bi-mode multiple-units are supposed to save ‘approximately’ 15 minutes between London and Cardiff, a loss of two minutes, while not critical, will make a difference.

According to the stakeholder letter, a ‘temporary solution’ is to be put in place pending reconstruction ‘as early as possible in Control Period 6’, which starts on 1 April 2019. A check with the ever-helpful Western Route media team brought the following amplification.

‘Network Rail is progressing detailed design for a track slew, to be implemented in December 2017, which will maximise the electrical clearances and minimise overhead line gradients between Steventon bridge and the adjacent Stocks Lane level crossing, and so facilitate electric traction to Swindon in 2018. This represents a temporary solution due to the deferral of bridge reconstruction until Control Period 6 (2019), but the wire gradient determined by the detailed design will necessitate a speed restriction to electric traction, which is at present being determined’.


So far so as expected. But the note concluded, ‘Concurrently, we are exploring the IEP Train’s Traction Power Change-Over capabilities and whether a change to diesel power east of Didcot station could be utilised to reduce the number of trains impacted by the speed restriction to electric traction’.

So yet again discontinuous electrification raises its insidious head. Or to put it another way, the infrastructure engineers are dumping their problems on the traction engineers to solve. In all fairness, I should add that when I put this theory to Network Rail Chief Executive Mark Carne the other day he dismissed it as ‘ridiculous’.

Work is still underway on the Automatic Power Change Over (APCO) system for the Great Western Class 800 fleet. This will use the standard Eurobalise, developed for the European Train Control System.

Brunel bridge at Steventon: a tractor on ballast levelling duties during an engineers’ possession of the Great Western main line on 19 February 2005. The road on the now infamous bridge is much quieter since the parallel A34 became a major trunk road
M. John Stretton

Messages, or ‘telegrams’, generated by the Eurobalise are defined as ‘Packets’. Packet 44 allows a balise to transmit data used by applications outside the ERTMS/ETCS system. This is already being used for the Class 390 Tilt Authorisation and Speed Supervision (TASS) system on the West Coast main line.

As the acronym implies, TASS tells the Pendolino when it can tilt, and at what speed, and then monitors that the speed is not exceeded. For APCO the telegram would alert the Class 800 to an upcoming change from electric to diesel traction, or vice versa, triggering the train’s automatic switchover. Manual change between traction will also be available.


So the theory is that leaving Didcot a balise some distance ahead of the bridge/crossing would instruct the Class 800, or both units running in multiple, to start up the engines, switch to diesel traction and lower the pantograph. Some distance after the bridge/crossing another balise would initiate the reverse process. The same sequence would happen in the opposite direction.

Now the distance between the two balises is going to be of interest to the MTU engineers who are not only responsible for maintaining their diesel engines but have no doubt been nailed down by Hitachi to some demanding performance and reliability guarantees. Don’t forget that the Class 800 engines with a rating of 700kW (950hp) were initially set to run at 560kW (750hp) in the interests of reliability.

‘Highland Chieftain’: the 09.40 Inverness – London King’s Cross heads south from Perth at Forteviot on 27 December 2015, with flooded fields to be seen in the distance. Some commentators predict that using an IEP on this run could add more than 10 minutes to the schedule
Ian Lothian


Talking of which, as we know, once the Department for Transport’s irrational belief in the power of distributed traction to multiply installed horse power and provide incredible accelerative powers was exposed, there was no way the Inter-city Express Programme Train (IET) was going to keep to IC125 timings pending electrification. So DfT had to plead with Agility Trains West, the organisation that owns and maintains the GWR IET fleet, to run the engines at the nominal rating. This should give a similar performance to IC125.

When this up-rating was linked with changing GWR’s nine-car Class 801 EMUs to bi-modes, the cost of the IEP contract went up by £300 million. But has the deal been done?

Questioned on the additional cost of the increased diesel mileage of the Great Western Class 800 bi-mode fleet until electrified services start in December 2018, the transport spokesman in the House of Lords replied on 21 September that the Department for Transport is still in discussions to amend the Great Western main line Inter-city Express contract. Really? With the first trains now in passenger service?


What we do know is that having had to cough up serious money to avoid having a fleet of no-go show-boats running on the GWR, DfT was not going to negotiate a second very expensive variation order for the East Coast IEP fleet. This includes 10 five-car and 13 nine-car bi-modes.

As a result, a nine-car bi-mode with five engines at the original derated output will have around 8.7hp/tonne, compared with around 10hp/tonne for the nine-car IC125 used by Virgin Trains East Coast.

And since the basic formula of power = speed x tractive effort is immune to the number of powered axles, it is going to be a long slow slog up the climbs on the way to Aberdeen and Inverness.

VTEC tells me timings have yet to be modelled. Informed sources suggest current timetables will have to be adjusted.


Sorry, I got diverted from the issue of why engineers won’t like the Steventon bridge bi-mode solution. What diesel engines like is sitting there, with temperatures and pressures stable, running at constant speed and power. As we know, high-speed diesel train operation UK-style is not like that.

Paxman identified binary driving, with the controller used as an off-off switch, as a cause of some of the woes that afflicted the original engine in the IC125 power car. But just as harmful, if not worse, is starting an engine from cold, running it at full power for a short time and then shutting it down.

MTU engines in the repowered Class 43 IC125 power cars have a system to preheat the coolant before start-up. An interlock prevents the engine from starting until the specified coolant temperature is reached.

Given the sensitivity over IEP reliability I was surprised to learn that while the smaller MTU engines in the bi-modes have preheat, there is no interlock, meaning they can be fired up from cold and set to work.

Class 800s running through to Aberdeen and Inverness will get a message approaching Edinburgh to switch on the coolant preheating. Opening the doors on arrival in Edinburgh will initiate APCO.

There is also the question of the distance required at 125mph to go through the changeover process. Once again, there will be time needed to check that all engines are firing and that the pantograph really is down in the well.

And all that’s before you get into the reliability of the balise and the auto-changeover system. So the thought that Network Rail’s infrastructure problems are being offloaded onto the train operators is perhaps not so ridiculous as it might seem to the layman.