The original platforms were on a curve as the line used to go onto Stonehouse and Strathven. When the line was reopened, the platforms were not built on a curve, instead built straight making it more difficult to extend the line because the platforms are in the way!
Presumably there are issues with future extending beyond Larkhall, hence why the platforms are straight
Equally, if the line is extended then one of the platforms can remain in use whilst the other is demolished, unlike Drumgelloch which had to be closed
The same parallels exist in road building, the footprints were in place for extending the M8, M77, M74, and M80, yet none of these were used most were removed and rebuilt, and in the case of the M8 the one at the Kingston Bridge isn't even going to be used and left in place!
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add to that, that the new airdrie to bathgate route was built to accomodate 20/21 metre units... and tha class 380s (last i checked) were barred from operating on the route
As above, the route was built with Class 334 / 380 use taken into account and the Class 380 has not yet been added (there is little or no point, and the same applies on other routes)
The platforms are more than capable of coping with 3 or 6 car Class 380 units of 69 and 138 metres :
Airdrie P2 130 metres, P3 150 metres (P2 may have been extended since ROTR 2011)
Armadale 150 metres
Bathgate 150 metres
Blackridge 150 metres
Caldercruix 150 metres
Drumgelloch 150 metres
The main issue would be other stations on the route, clearly many would require extending
Equally, Glasgow QS LL is only 135 metres, but these could also be extended
Personally, I cannot see this being relevant unless more Class 380 units being ordered or cascaded which I think is very unlikely for at least the next 10 years