Late departures from New Street are not solely due to passenger loading but because of the sheer effort of trying to squeeze a quart into a pint pot. Yes there are issues with passengers congregating at the bottom of the stairs and only using the door immediately in front of them, but that also happens with 11 car Pendolinos so perhaps train length is a red herring.
The major cause of delays at New Street is down to the large number of services arriving and departing, the number of conflicting movements in the station throat (and beyond) and only having two lines in and out at each end.
I don't believe that train length is a red herring. Yes there is an issue with passengers congregating around the bottom of the stairs at New Street, as at many stations, but daily personal experience demonstrates that passengers do spread themselves along the length of the imminent Crosscountry train, but a 4 car 220 only offers 69 metres of platform for perhaps 200 standard class passengers to spread themselves along. In normal service I often notice a cumulative delay at consecutive stations on services formed 4 car vice the booked 5, and the opposite effect when a 5 car deputises for a 4.
Number of services is a separate but very much valid concern when essentially a train every five minutes is being forced through the Birmingham - Wolverhampton corridor on at least one side of the hour, with a variety of stopping patterns and performance characteristics: There's no room for recovery once one train ends up delayed. The same must apply to the Coventry - Birmingham side too, especially with the increased Avanti Pendolino service.
But you cannot divorce train capacity from infrastructure capacity. It's not a question of operational convenience but about making sure that you maximise the capacity you have available. The capacity at New Street is constrained by the number of platforms available and the access to them. If you're suddenly losing a half platform because one service is suddenly longer and needs the entire platform length, then you have potentially one service waiting outside for it to depart when it would have previously pulled up behind. Clearly you can see how this would have an impact on all the other service operating around it that also require access to New Street. If you lengthen services so that they are no longer able to share platforms then someone somewhere is going to suffer.
Indeed, I certainly do appreciate the potential knock on effects on overall capacity, but operating short trains to suit platform availability IS operational convenience over passenger convenience. I mean, howay, if West Coast were currently operating solely a fleet of 6-car Pendolinos between Euston and Birmingham, with the same number of passengers at present, to suit the fact that terminating services only used one half platform, would anyone really be arguing that that's all that could be done? The clamourings for HS2 would be even louder than they are at present.
Crosscountry's HSTs pass through New Street several times a day, on various services over the course of a week, and obviously need a platform all to themselves (There are also some daily double Voyager services with the same requirement): Given the train planning desire to keep things as standardised as possible, particularly with a clock face hourly timetable, are the other services much different? In times of disruption, perhaps it offers some element of flexibility.
It happens perhaps more than you imagine. Plus if you're only going to strengthen one train per hour when there are eight arrivals and departures per hour (two each to and from Manchester, the North-East/Scotland, the South-West and the South Coast every hour) then you're hardly addressing the capacity issue.
Using 8-car formations on Scotland - South West services targets what I have seen as the services most in need of increased capacity: Everything else that's currently 4-car being expanded to 5-car would be sufficient in many instances and doesn't sacrifice platform capacity at locations where use of half or short platforms is operationally convenient. There's an all day 8-car diagram each Friday on Manchester - Bournemouth, so additional strengthening if possible of targeted busy services presumably wouldn't be insurmountable anyway.
There are short platforms also on the Nottingham route, but with the exception of Willington they can all accommodate 4 cars.
Ah I'd forgotten about Willington, despite having used it once in the past.
I don't think that's how it works. Rolling stock cascades are in any case controlled by the DfT who seem to be linking them solely to newly let franchises. I don't imagine for one moment that they are unaware of the overcrowding situation on XC, but they are not prepared to do much of anything about it at the moment.
I've worked on both the franchising and operator sides of the railway, that's exactly how it works: The rolling stock strategy is set at the start of a franchise when DfT choose a winning bidder. This is tied to annual premium, subsidy and revenue targets that permit little to no deviation from that plan. Crosscountry have been tied into a direct award since October 2016, with an optional year which has been taken up that takes them through to October 2020. Had the franchise been fully relet at some point in the interim then potential new operators would have been closer to the front of the queue to enter negotiations with the leasing companies to secure additional 170s ahead of both Transport for Wales and East Midlands Railway. As it is that ship has long since sailed and XC are left scrabbling for the scraps dropped from other operator's tables.