Yes the geography is such that the ideal (assuming double track throughout is not going to happen) is 2 loops, one near Lacock, the other near the former Holt junction station.

Reasoning is trackbed is easiest to do at these, remember it was originally broad gauge double track, so not a case of squeezing a track in. And don't want to add tracks where it has been slewed under centre of old arched bridges.

I think current policy is to build freight loops suitable for 775m long trains, so roughly half mile long loops.  Can either built them as reversible loops with slow speed junctions, (waiting train uses them, other train passes at speed), or as short double track sections.  The former needs more signals, the second is speed restrictive both directions unless long faster points are installed.

My gut feeling is having a loop at Melksham station and building a fully accessible two platform station might will cost more than two loops where space exists.

 
1 is Limerick Junction, post the 1967 alterations I think looking at the converging paintwork in the extreme right.

A complication here was that all trains had to reverse into their respective platforms.

 
Some interesting examples.

Personally I believe the best option is a loop away from the station itself.  Given the length of some freight trains you would very quickly be outside the station limits if sited there.   An ideal location would be near either end of the single line.  This would have the added benefit of being able to get a train off the main line to prevent it blocking the path of other services while it waits for a slot through to the other end.

At the very least an intermediate signal between the junctions so trains, in the same direction, could be "flighted".

Of course the perfect solution would be double tracking throughout....

 
Bridges and lifts at stations are expensive to provide - but if we want to increase the number of trains calling at Melksham, a single line all the way from the outskirts of Chippenham to the outskirts of Trowbridge won't pass muster.  Here are various ways from around Europe - including tbe British Isles - that multiple services can call at stations in each direction at more or less the same time.  Some of these would have the powers that be throwing their hands up in horror. Others are not very passenger friendly. But there are some that are proven to work in a British environment.

Two tracks (i.e a passing loop) with a diamond crossing to bring each to a long platform


A narrow outer platform used by the train which is going to have least passengers joining


A long platform with a loop past one half.  Train arrives into looped platform, second train arrives into other end then leaves around loop, first arrival then carries on


Ditto - but British example showing that this CAN be done in the UK. And there would be space at Melksham


Another example of an outer platform with a flat crossing - in this case the second platform is much wider


Where more passengers will cross the line, level crossing barriers can be provided and that's sometimes doe for a significnat number of passengers.


Single platform and bring in two trains end to end, have all the through passengers swap over, and then both trains go back whence they came.  There is a British example on the Great Orme Tramway, and an example of passenger swap both ways at Mockava.


Have a platform on each track, but simply use a slope up to an existing bridge that carries a public road / right of way for passengers to cross over.