Speed restrictions of 40mph will be enforced on a diversion route around a section of the City Bypass set to close later this year to cater for Borders Railway works.
Network Rail has revealed an alternative two-lane carriageway will be used for at least eight months starting from September while a 130ft-wide tunnel is excavated beneath the vital road link.
A speed limit of 70mph usually applies on one of the Capital’s busiest stretches of road, but Britain’s rail network operator has said it does not expect the new restrictions to cause added travel chaos.
The traffic management plans were detailed as the main construction work to re-open the Waverley route from Edinburgh to Tweedbank, near Galashiels, was started today by principal contractor BAM Nuttall.
Initial earthworks will involve the excavation of the track alignment for the new line through Monktonhall and the removal of thousands of tonnes of material from the site of the new Shawfair station.
Commuters have been warned to expect hundreds of lorry movements along the A7, particularly south of Sheriffhall roundabout, each week for the next two years. The bypass works will allow a double track section of rail to pass under the A720, at a site about 200 metres east of Sheriffhall.
Network Rail project director Hugh Wark said the roundabout near the diversion already slowed traffic speeds.
He said: “Although there is a speed restriction on the diversion due to the curve in the road, we don’t believe there’ll be any major restriction in traffic flow. Indeed we believe the traffic will flow normally.
“There’ll be four lanes of traffic – two lanes in each direction will be maintained. There’ll be some lane closures at night to allow us to do the changeover.”
Bans will be in place preventing construction traffic from using mainly residential streets from Eskbank to Galashiels.
Traffic lights and lane closures will be expected along sections of the 35-mile route and reported on the website www.bordersrailway.co.uk.
Information sessions are being run in Newtongrange, Danderhall and Gorebridge over the next fortnight.
Excavation works will be heaviest near the Hardengreen roundabout and at Newtongrange. About 150,000 tonnes of material will be moved from just north of the City Bypass.
Mr Wark said: “We’re working to minimise the effect of existing traffic on the A7, but there’s no question there will be a lot of additional traffic.”
A recent report on the £300 million project to re-open the Borders rail link claimed the line’s existence would cut car journey numbers by 530,000 each year.
The line is due to open in summer 2015. Seven new stations are being created at Shawfair, Eskbank, Newtongrange, Gorebridge, Stow, Galashiels and Tweedbank.
Transport minister Keith Brown said the project would bring communities along the route back into the rail network for the first time in more than 40 years.
Rail consultant and author David Spaven, who has long campaigned for the re-opening of a Borders rail route, said: “It’s inevitable that there’s going to be disruption, but I think the vast majority of the people in the Borders and Midlothian will be willing to put up with a little bit of short-term frustration in return for a transformation in the quality of their public transport.”