RAIL commuters are being warned to expect delays and cancelled services as the next phase of a Scotland-wide programme of upgrades gets underway.

Work will begin on the railway network in Central and Northern Scotland next month with some routes out of Glasgow expected to be disrupted until the end of the year.

Passengers have been told to check train times ahead of their journeys and to expect to complete some trips by bus, especially after the peak evening period.

Journey times will be longer and customers can expect to see queuing systems in operation at key stations.

The Scotrail Alliance's upgrade programme is being carried out to increase overall reliability on the railways and pave the way for the introduction of greener electric trains.

However, it is likely to hit the operator's performance targets, which had been improving in recent months after falling beneath Scottish Government targets last year.

Chief among the routes affected will be the Glasgow Queen Street to Dundee, Aberdeen and Inverness line, with work taking place from Sunday to Thursday each week after 8pm until Sunday 10 September.

Travellers have been told trains may be diverted via Polmont or cancelled. The last trains of the day heading north will also depart earlier than usual.

Services from Glasgow Central and Alloa, Stirling and Perth will also be affected, with buses operating when there are no trains running. There are also warnings that trains running to Falkirk Grahamston may be cancelled until September.

The upgrading works will also affect trains running between the station and Edinburgh via Shotts, with cancellations at certain times of the day until December 7 at the earliest.

The Scotrail Alliance is a partnership between Scotrail franchise operator Abellio and Network Rail aimed at improving Scotland's railways.

As well as the track upgrade, £475 million is being spent upgrading the train fleet over the next seven years. This will see 75 per cent of its carriages either new or fully refurbished.

However, complaints about crowded service and cancelled trains are on the rise, and rose again between January 8 and February 4 this year.

ScotRail has a “key performance indicator” for the number of complaints for every 100,000 journeys. The figure has gone up from 29.1 complaints to 32.1 complaints - a 10 per cent rise on the same time last year.

The firm insists that its improvements are still on track, saying earlier this month that service performance had increased for the sixth month in a row.

The firm released a statement saying that 93 per cent of the its fleet met industry punctuality targets in the four weeks leading to March.

Jacqueline Taggart, ScotRail Alliance Customer Experience Director asked passengers to bear with the company while the latest works were carried out.

She said: “No one likes having their journey changed. However, this short term disruption will lead to a more reliable, better rail network that will rank amongst the very best.

“We are going through a massive period of change on Scotland’s railway. The work that we are carrying out over the next few months will bring about a revolution in rail, with more and better trains, more services and more seats than ever before.

“However, while we transform the railway, there is inevitably going to be some impact on people’s services. We are doing everything we can to minimise this, and to keep people moving.”