I'm not familiar with the inner workings of TPS, but each train will have two timing loads, one of which may be hidden from the user.
In Trainplan, which was used before TPS, both of these timing loads were visible to planners and could be independently altered if required.
The Trainplan Timing Load was used to calculate Sectional Running Times (SRT's) appropriate to the trains being planned. Additionally, there was a TSDB Timing Load, which was a much more simplified and limited value. It is the latter timing load that appears in the CIF.
A Trainplan Timing Load would automatically match to a TSDB Timing Load, but it was possible to subsequently alter the TSDB Timing Load to a different value. This was very useful if, for example, running trains over routes they don't normally work, where the relevant Trainplan Timing Load was not populated with SRT's. Other uses include changing traction type, if being replaced by something that can achieve the SRT's.
Not all tools in Train Planners' armoury are visible to end users, as they don't make it into the CIF. Three types of timing allowance are visible in TRUST and online systems - engineering, pathing and performance, but a fourth, adjustment allowance, isn't. This is a vital tool for planners, but is invisible to anybody without access to planning software. It is used to extend or reduce SRT's where required, such as differential speed junctions or when the timing load is not wholly appropriate to the train being timed. Despite what many people assume, timings are not held in the planning software for all trains over all routes. In fact, when it comes to charters and other one-off movements, it is highly unlikely that any SRT's exist in the software for that specific train. A train shown as timed to a maximum speed of 75mph or 95mph may not actually have been timed as such, that is just what the CIF outputs. Changes of Timing Load can also be made en-route.
I am pleased to see these officially approved open online systems, but do feel that many of the questions arising are simply due to people over-analysing things that don't really need to be analysed!
I hope this gives a better understanding of some of the issues raised in this thread and in some others.
