Rail chiefs have urged Lenzie and Bishopbriggs commuters to swap the train for the bus during 20 weeks of works at Glasgow Queen Street Station.
And there have been warnings that those opting for the train could face a long wait - with the possibility of trains being full.
A new timetable being introduced from March 20 will see trains continue to operate half hourly, but take arond 25 minutes longer to reach Glasgow.
First Glasgow will be providing an extra 600 seats at peak times to take the strain, and the Scotrail Alliance hopes commuters will take advantage of them until normal service resumes on Monday, August 8.
Service 89 from Bishopbriggs will have four more services in the peak, and Service X85 from Lenzie will also have a further four.
A ScotRail spokeswoman said: “By diverting trains to Queen Street Low Level, we’re ensuring that Lenzie and Bishopbriggs customers will still have a direct rail link to the city.
“However, trains are likely to be extremely busy at peak times – due to numbers boarding further up the line - and people may not be able to board the first train they aim to catch.
“These 600 extra seats give customers an attractive option for travel during the tunnel closure. Journey times into Glasgow are likely to be around 20 minutes. People can simply buy a bus ticket when boarding.”
A First Glasgow spokesperson added: “Working in partnership with ScotRail, we’ll do our best to keep people moving in and out of the city for the duration of these works.
“First offers fast and frequent services in and out of the city centre and tickets can be bought via our smart phone app to make bus travel even easier.”
Bus information and a journey planner can be found at www.firstglasgow.com
Fr more information about the changed train timetable visit www.scotrail.co.uk/QueenStreetTunnel