RAIL passengers using the busiest commuter routes in Central Scotland are being urged to set off around half an hour earlier than normal from tomorrow [Sat] as major engineering works get underway between Glasgow and Edinburgh.

Passengers travelling between Scotland's two biggest cities face six weeks of disruption, with replacement buses on some routes and other services much busier than usual.

ScotRail has been ramping up its awareness campaign in the final days before the Winchburgh Tunnel works begin, with managers deployed in affected stations in recent days to help customers plan their journeys.

There will be no services to and from Glasgow Queen High Level and Edinburgh from tomorrow until July 27, meaning the flagship shuttle service - which normally runs every 15 minutes - will be unavailable.

Instead, commuters looking to travel end-to-end between the two cities will have to use replacement buses to and from Linlithgow, take the slower Queen Street low level trains or use the longer route from Glasgow Central.

This could add up to 40 minutes to a typical journey during the morning rush hour.

ScotRail is urging passengers to set off around 30 minutes earlier than normal but warned customers boarding at midway stops such as Motherwell or Bathgate that demand for space may mean they are unable to get on the first train.

Cyclists face "significantly reduced capacity for bikes", and the Open Golf Championship taking place at St Andrews from July 12 to 19 will heap further pressure on the network.

ScotRail said it would have more than 200 additional staff on the ground to assist customers across nine locations, supplemented by over 40 dedicated bus co-ordinators.

Forty-four buses will cover services between Linlithgow, Edinburgh Park, Haymarket and Edinburgh, with additional buses on standby.

A spokeswoman for ScotRail said: "We are putting together the final touches to our Winchburgh preparations. It's clear that most of our regular travellers are aware of the changes and the need to allow more time. The next step is to plan their journey in more detail, which we are encouraging them to do via our website, app or by speaking to staff."

It is the biggest upheaval to rail services across the Central Belt since the £742 million Edinburgh-Glasgow Improvement Programme (EGIP) began in 2011.

The Winchburgh Tunnel, near Linlithgow, will close while the track is removed and the floor of the tunnel lowered so that power lines can be installed as part of the wider electrification project which will pave the way to "faster, bigger and greener" electric trains - eventually cutting journey times between the cities to 42 minutes in 2018.

Rodger Querns, programme director of EGIP for Network Rail, said: "We do appreciate the inconvenience this will cause passengers. We have planned the work meticulously and are working hard to minimise that disruption.

"We are working round-the-clock. We have engineers on the site 24/7 to get the railway back running as planned on July 27."