So which of the above applies to HST trailers? Overused IMO. Everyone wants shiny and new if someone else is paying...
What's wrong with the HST trailers ?
Corrosion. Accessibility. Wiring. Performance. Fatigue. Maintenance.
Corrosion is the main problem, only the best vehicles will be taken forward to be fitted with power doors. They've suffered significant corrosion at the vehicle ends for years, principally from the unsealed gangways, from the doors, from the water tanks in the roof space and from the human sewage coating the underside of the vehicles.
That has needed significant corrosion repair in the trailer end roof voids, around the gangways, and underneath the vestibule floors (both inside and out) with a number of vehicles suffering significant corrosion on the bogie pivot point. We've seen a few vehicles being cut because of corrosion issues.
This bogie design isn't brilliant and provokes ballast pick-up, which has destroyed the underbody skirts (most are on their second set of skirts and a third set will be needed for those vehicles being used in future). The loss of rotten parts of the underbody skirts at speed is the usual reason for air pipe failures.
The bogie design ballast pickup also hits the wheelslip protection wiring, VTEC are investing in additional ballistic protection for this to cut failures. WSP failures cause wheelflats which in return need more vehicles out of service for wheel turning.
Accessibility
They need power doors fitted or significant modification to the slam door to allow the doors to be opened from the inside.
They also need passenger information systems installed and quite probably a digital seat reservation system to fit in with the looming digitisation of seat reservation.
That's work which starts to become really rather expensive, and is likely to uncover numerous additional problems which may require further remedial action over and above that which is budgeted.
The sensible option to continue HST use for more than a handful of years is shotblast each bodyshell back to bare metal, do the necessary metal thickness testing and then decide which bodyshells aren't suitable for reuse.
Wiring will need replaced or significantly modified to provide power for power doors, where they're chosen to be fitted. If additional toilet modules are added or removed, there's further modification to wiring to be undertaken. That's a lot of work and a lot of time necessary to design, manufacture and rewire new wiring looms for each vehicle.
Performance will always be an issue unless you double the installed power in the powercars, with new engines, new alternators, new traction motors, new bogies and new cooler groups. That's a new locomotive at each end of the formation. And they still cannot do 140mph.
When you cannot fit an extra train or two per hour on already busy sections of railway it just kills any capacity enhancement, so increasing accelerative performance is a massively important piece of the puzzle in increasing capacity. The most you could do is take over Mark 3 stock from elsewhere (but where, since we don't want to retire Mark 3 stock) and add 1 more vehicle into the Great Western HST formations. That comes at the cost of slower acceleration though and more pathing constraints.
Fatigue has been an issue in the past and will again become an issue to contend with. The bogies will not last forever, the metal will become too thin, they'll need parts re-machined and ultimately they'll be at ever increasing risk of failing their ultrasonic/NDT inspections.
The alternative is new bogies, which you'll probably need if upgrading the traction motors on the power cars, but new bogies, perhaps light weight lower axle loading inside frame bogies for the trailers would be viable and possibly essential if you're to get considerably longer life out of HST. It would lower the track access costs, but they're already negligible on trailers anyway.
Maintenance is the killer blow - keeping 8 or 9 vehicles together and sending them to remote parts of the network on late arriving and early departing services reduces the amount of time that's available to maintain 11 vehicles, being able to drop off 5 vehicles as the service goes by a depot is brilliant and will only serve to increase reliability and availability.
The mixture of bi-mode and all electric stock with a mix of both types on different diagrams is going to allow a unit with a failed diesel power pack to continue on in service on electric power rather than having to come out of service. That could be at Edinburgh as an example, where a unit arriving from London can't continue to Aberdeen, but a unit arriving from Inverness or Aberdeen can be swapped over - inconvenient, undoubtedly, but not service cancelling inconvenient.
And units with AC traction motors are inherently more reliable than locomotives/power cars with DC motors. IEP is going to really improve on the HST and IC225 reliability providing fewer in service failures and better availability. Hitachi have put together a really incredibly well engineered package with excellent design and excellent maintainability.
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Whats the penalty with IC225 (short) over IEP will it actually work leaving Edinburgh? Also does the IEP end up catching Scotrail services to North Berwick when departing Edinburgh?
IC225 in short formation is in short formation to match IEP timings - much like 2+5 HST sets matching Voyager timings on the XC timetable.
IEP will be following AT200 stock into Edinburgh, they should be slightly faster accelerating compared to IEP being geared for lower speeds, and the rest is down to pathing.
