Princes Street, including the pavement running alongside Princes Street Gardens, is to be closed between South St David Street and South Charlotte Street from Saturday 21 February.
Buses and taxis will be diverted along George Street, in a repeat of a move which snarled traffic during the aborted Mound closure in October 2008.
Several chief spokesmen for the project have issued reassurances about the scale of disruption and their confidence in the necessity and wisdom of the decision.
David Mackay, Chairman of Transport Initiatives Edinburgh (TIE), said: “TIE has, as ever, considered the views and needs of retailers and businesses into our planning and we are confident that this plan is the best solution for all.”
The arrangement is seen by administrators as preferable to single direction closures which would extend the duration of building work considerably.
Works will be halted in August during the Edinburgh Festival in an effort to reduce the impact on tourism and Princes Street retailers.
Councilor Phil Wheeler, transport convener at the City of Edinburgh Council, said: “This is a pivotal stage in the trams project and I am confident that following extensive traffic modeling we can keep the traffic in Edinburgh moving.”
Mr Wheeler stressed the importance of keeping Edinburgh’s pedestrians well informed via "a multi-media advertising campaign" and additional signage.
Crucially, he said, shoppers should be aware that all shops will be open for business during this time.
Ian Craig of Lothian Buses acknowledged the impact on bus services. “A diversion on this scale will inevitably mean some disruption to bus passengers," he said.
“Information about the diversion will be widely distributed via our buses, travel shops and of course downloadable from our website."
A spokesperson for Edinburgh Trams emphasised that “traffic flow and the performance of these measures will be under constant scrutiny from all three organisations.
"Necessary changes will be swiftly implemented and contingencies are in place.”
Work will not begin on the west-bound lane until the end of the first week of the closure in case - despite the "meticulously planned" traffic management measures - TIE and partners have underestimated its impact.
www.lothianbuses.com