Big Jumby 74
Member
Absolutely. BUT, in the early days of Desiro's (2004 timetable) there were planning rules that essentially barred that scenario, not for any physical/non compatible (stock) reason, but more to do with a desire for a robust timetable and good performance. Any odd mixed formations were seen (back then) as a potential performance risk, in the sense that for example, if said formation became reversed for any reason, it could lead to problems with the timetable (wrong unit/s on wrong services etc), which in the peak hours could prove a real problem. Just to demonstrate my point: If a 9 car (450 leading/444 trailing) came in to Waterloo (or Portsmouth Harbour for that matter), and was diagrammed to split, the 444 on the rear then departing separately, leaving the 4 car 450 on the blocks, to form the rear part of another train. The front part of that latter train (an 8 car 450) arriving after the 444 had gone, and attaching to the 4 car on the blocks to form an outgoing 12 car 450. All well and good in the plan, BUT what if the mixed formation had become reversed before the detachment, incorrectly formed up earlier perhaps or diverted (unscheduled) off route, such as a 1P run via Southampton due to a line blockage. Rare perhaps but still possible - end result an 8 car 450 enters the terminus later to attach to what should be a 4 car 450, only for the driver to find on entering the platform a 5 car 444 in front of them. The signallers would not necessarily know the inbound train was reverse formed - end result, either at PH or Waterloo, the job get partially stopped due to 13 cars trying to occupy a 12 car platform.
That's just one example of why certain rules applied to the preparation of the base plan timetables over the years. Keep the plans as simple as possible within the requirements of the job, therefore the timetable should prove more robust/resilient, which benefits everyone, particularly the fare paying passengers. The mileage limitations on the Desiro's did cause some compromises in this regard, including the decision to have mixed formations on the Poole/Portsmouth splitters on Sundays - a decision that was not taken lightly, but the alternative was a breech of the financial contract.
