Great Western Coffee Shop

Why does it always seem to take so l-o-n-g to get past Tisbury?  Quite apart from the station stop, there seems to be a boring dwell at the loop - double frustrating if the you add in other dawdles of London to Exeter trains around and in Wiltshire ... from 1L33, the 12:20 from Waterloo, today, as read off Real time trains (https://www.realtimetrains.co.uk/service/gb-nr:L52594/2021-12-01/detailed#allox_id=1) (this link will expire in a week):
* 3 minutes "pathing allowance" at Andover
* 2.5 minutes "pathing allowance" on the approach to Tunnel Junction
* 4 minutes in the station in Salisbury
* 4.5 minutes gap between arrival and departure from "Tisbury Loop"

From Open Train Times (https://www.opentraintimes.com/maps/signalling/westofengland), the setup at Tisbury looks different to that at other places trains can pass each other in the same region:

(http://www.wellho.net/pix/tisloop.jpg)

To my untutored eye, it's almost as if Tisbury is set up to hold a freight train or an ECS off to one side - in either direction - and then have a passenger train, for which perhaps a faster schedule is important, run straight through.  The wait in the example train above suggests that, whist it can be used to pass passenger trains, it's far from ideal for that.  Have I read that right?

1F18 - the Portsmouth to Cardiff train that leaves Salisbury just ONE MINUTE before the arrival of the service from Waterloo - is an example of a train with less slack across Salisbury. I took a look at this train just wondering if it could hang on for a couple of minutes. Longer stations stops are:
* 4 minutes at Southampton
* 2 minutes at Salisbury
* 2 minutes at Westbury
There are no passing loop waits and no pathing allowances in there - but there are two "engineering allowances" of a minute each at Warminster and at Bradford-on-Avon.  Further north, 2 minutes at Bath Spa and 7 minutes at Bristol Temple Meads, and a minute engineering at Bath Spa and 30 seconds pathing on the approach to Bristol.

There are other issues in moving the slack around. We need to remember that from Tunnel Junction into Salisbury Station, and from Salisbury Station to Wilton Junction, the trains (under current layout / signalling) share the same track. Also that the "minimum interchange time" between trains at Salisbury is 5 minutes, though cross platform (2 to 3 or vice versa) or along platform 4 (rear train to train in front) perhaps a minute or two less could be managed in practice.

The loop at Tisbury was very much an afterthought following the singling of the line west of Wilton. The powers that be had intended the line to be single all of the way between Gillingham (Dorset) and Wilton, but this proved disastrous for timekeeping. As the land adjacent to the Down platform at Tisbury had already been sold off, they could not put the loop in the station itself. In the current timetable, a number of westbound trains are scheduled to wait in the loop.

Templecombe is another one where the double track should continue into the station not start a few metres to the west.
However any future changes will wait until the decision is made about electrification (or not) and the replacement for the 159s.

The former site of the down platform is part of a hardstanding surrounding a large commercial building. I am sure if the will was there the current owners could be persuaded to sell back a few metres width to allow reinstatement of a platform (& footbridge if that is deemed necessary). Every time I use the SWR route through Tisbury the commercial site seems bereft of any activity.

What does an 'engineering allowance ' actually mean?

I believe it's time sprinkled into schedules to allow trains to catch up if they've had to go slower (so take longer) through engineering works (temporary speed restrictions)