The china clay train that supplies the Caledonian paper mill in Irvine comes up from England every week hauled by a Class 92 electric locomotive. It comes up the West Coast main line to Mossed, where the 92 is swapped for a Class 66 diesel loco. It then goes down the Ayrshire coast to Barassie, reverses and heads into the exchange siding at the paper mill where the mill’s shunter takes over. That’s 3 different locos for one train travelling over an unnecessarily long route. What if the 92 could take the train all the way to the exchange sidings? Well this would require wires running along the Barassie line and into the siding. But wait! The line down from Glasgow via Kilwinning is wired, but this still takes the train the long way round. The shortest route from England is to come up the Glasgow & South Western main line via Dumfries and Kilmarnock, which at the moment is unelectrified. Now there’s no point electrifying that entire line for one weekly freight train, so now we have to look at passenger train use of the line.
There are essentially four passenger trains on this route There’s the stopping commuter service from Barrhead to Glasgow, the fast service from Kilmarnock to Glasgow and it‘s opposite equivalent from Dumfries to Carlisle, the Kilmarnock-Girvan shuttle and the 2-hourly long-distance service from Glasgow to Carlisle that serves Auchinleck, New Cumnock, Kirkconnel and Sanquhar. Thus the railway could be electrified in stages: From the Glasgow end to Barrhead first, then to Kilmarnock and from the Carlisle direction to Dumfries, then the “middle” section between Dumfries and Kilmarnock. The section to Barassie might be tricky, because to supply the only passenger train on the branch would also require the Ayr-Girvan line to be electrified at the same time.
Network Rail’s Route Specifications 2012 document suggests the electrification of the Glasgow to Kilmarnock and East Kilbride lines (the East Kilbride branch comes off the Sou’Western at Busby junction just south of Pollokshaws West) in control period 5. It also suggests the route could be an “electrified diversionary route from Ayr” (implying electrification of the line from Barassie, which would serve our china clay train) but does not make a firm commitment, merely listing such a route as a “future aspiration” No electrification south of Kilmarnock is currently proposed, possibly due to the low frequency of passenger trains. However, the route also sees occasional EMUs heading to Wabtec and Brodie’s in Kilmarnock, which could potentially be electrically hauled. There are also diverted trains from the West Coast Main Line, which currently have to be hauled by a diesel locomotive. An electrified Sou’Western line would therefore be strategically useful.