As a regular user Bath to Salisbury can certainly agree with others that this service can be very overcrowded. The end of working day services form BTM towards Trowbridge can be packed with more wanting to get on at Bath and the reverse is true (particularly the early trains getting people to Bath and Bristol)
There is a respite for the Saturday/Sunday services going down to Southampton for the football - will be interesting to see how elevation to the Premiership will affect those trains

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Other times I have seen very crowded trains include when a ships company of RN sailors climb aboard at Pompey (still happens). They tend to be coming back off a long tour and the train tends to become a mobile pub ain the times I have been aboard! Lots of luggage too.
Despite what I have said I rarely have had severe delays (about the worst was when a preceding service hit a cow on the line after Bradford upon Avon. When we did get going we had the announcement that looking out the windows was not recommended... which guaranteed everyone staring out the window to view the results of a 158 hitting a large cow).
The bad old days of the 2 unit 158 are now thankfully over on that route. The best journey was when there service I got from Portsmouth going back to bath late (after 9pm) turned up with 7 or 8 units - bliss - had a carriage to myself even with the rear few carriages dark and locked off.
There are times when an 8 coach set would not be enough but overall over the past 15 years of using the service it has been pretty reliable although very hot in the warm summer days.
In respect of the disabled accessible seating - the best thing I can say on this - it is always reassuring to see that where assistance is requested it has been given readily and reserved seats are swiftly made available if occupied!
Not a lot to see until you get to Westbury where you can see some of the heavy diesels moving the quarry wagons around, after that the break into the water views on the final run into Southampton.
C