Snowploughs and gritting teams were this morning struggling to get access to the structure because of the massive tailbacks.
The situation was made worse by a broken down lorry at Admiralty and a spate of minor accidents.
Some drivers tried to divert from Fife to the Kincardine Bridge, but quickly found themselves caught in gridlock in the white out conditions.
Parts of the Edinburgh City Bypass were reduced to one lane.
The AA said it had fielded more than 100,000 calls since Thursday – making this the busiest episode in its 105 year history.
Tayside Police urged drivers not to venture out at all because of white out conditions on the A9, M90 and A90.
A spokesman said: “Stay at home, stay warm and stay safe.”
Edinburgh Airport was forced to abandon any hope of flights saying its runway would remain out of commission for the entire day.
Bus services were badly disrupted.
Train services between Edinburgh and Dunbar were suspended, the main Edinburgh to Glasgow line was reduced to a half hour service, while the Fife Circle routes were subject to delays and cancellations.
Hundreds of schools across East Lothian, West Lothian, Mid Lothian and Fife were shut for a third day.
City of Edinburgh Council said it hoped to open at least some primary schools and some secondary schools to senior pupils, but Mid Lothian Council and East Lothian Council confirmed that all of their schools would remain closed until Monday.
NHS Lothian reported on both its Twitter and Facebook social networking sites that its switchboard staff had answered more than 15,000 calls yesterday.
And two of Scotland’s biggest tourist attractions – Edinburgh Castle and Edinburgh Zoo – were also forced to close for the day.
A spokeswoman for Edinburgh Zoo said: “Due to the snowfall overnight we made the decision to close the zoo because of health and safety reasons as many of the paths have not been cleared.
“We hope to reopen as soon as possible but at the moment we are just taking it as it comes.
“With regards to tomorrow, we willbe making a decision early on as to whether or not we will open and visitors can check our website for regular updates.”
A spokesperson for Historic Scotland said: “Our team were on site from early this morning clearing the snow from the castle.
“We gritted and cleared a path around the castle numerous times but continued snow showers made the path unusable and the decision was taken at 10.30am not to open the grounds of public safety.
“We are really disappointed not to be able to welcome visitors through the castle doors today, but will continue to review the situation and would urge any prospective visitors to check the website or phone before travelling tomorrow.”
Further heavy snowfalls of up to 15cm have been forecast with freezing temperatures expected to bring icy conditions too.