Network Rail engineers are to renew and extend track, signalling and overhead power lines as part of a £170million project to increase capacity on one of country's busiest routes.

But the work means some train services are being diverted and others replaced by buses during the work.

Changes include:

l On the Glasgow Central - Ardrossan / Ayr / Largs line, services will start and terminate at Paisley Gilmour Street, but passengers should change at Johnstone for direct bus services between Johnstone and Glasgow Central. There will also be a bus service between Glasgow Central and Ardrossan Harbour to connect with ferry services.

l On the Glasgow Central - Stranraer line, services will be diverted via Kilmarnock, extending journey times. Passengers travelling to / from stations between Ayr and Stranraer should travel to Ayr and change for services to Stranraer.

l On the Glasgow Central - Gourock / Wemyss Bay line services will start and terminate at Paisley Gilmour Street, with a replacement bus service operating between Paisley Gilmour Street and Glasgow Central. Certain services on this line will be cancelled on some days.

Once complete, in January, the Paisley Corridor Improvements project will boost flexibility and allow for increased levels of service between Glasgow and Ayrshire, Renfrewshire and Inverclyde.

David Simpson, Network Rail route managing director Scotland, said: "The complex nature of these enhancements mean they can only be delivered through short-term closure of the lines, but our engineers will work as quickly as possible."

Jacqueline Dey, ScotRail operations director, added: "Full plans are in place to provide alternative transport arrangements where required."