The Forth Road Bridge has reopened to all vehicles after being closed by snow for the first time.
Both lanes opened in each direction at 1700 GMT, after the bridge had closed in the early hours.
Feta, the firm which runs the 46-year-old structure, said motorists should expect delays.
The road bridge had closed in "blizzard conditions" at 0630 GMT, after a jack-knifed lorry had earlier blocked both lanes, allowing heavy snow to build up.
Edinburgh Airport has also been closed and will not open until Thursday morning at the earliest.
Additional heavy snow clearing equipment was drafted in from Fife and Edinburgh Councils to help clear hard-packed snow on the road bridge.
Chris Tracey, Feta engineering services manager, said: "The team has been working flat out to clear what have been unprecedented levels of snowfall on the bridge.
"Nobody working here can remember such an accumulation of snow on the structure before.
"Our own snow-clearing equipment has coped with everything nature has thrown at the bridge over the past few decades, but today's conditions meant we had to call in extra help.
"The rest of the road network is still badly affected, so our advice to motorists remains to avoid travelling unless absolutely necessary."
Another jack-knifed lorry on the M8, half a mile from Junction 3a, meant the road eastbound was closed from 1115 GMT until 1315 GMT. The driver is being treated for back pain following the incident.
Meanwhile, all state schools in West Lothian, East Lothian, Midlothian and Fife were closed on Wednesday.
All state schools in Midlothian, West Lothian and East Lothian are now closed until Monday.
Most Fife schools will remain closed on Thursday but it will be up to individual headteachers to decide if their school can re-open.
Edinburgh school pupils in S4, S5 and S6 have been advised to go into school, except those at Queensferry High. Firrhill High School and St Thomas Of Aquins RC High School closed at 1300 GMT.
Cowgate, Calderglen and Tynecastle nurseries have reopened in the capital, as have Craigentinny, Broughton, James Gillespie's Primary School, Sciennes, Bruntsfield and Gylemuir primaries.
Leith and Lorne primaries are also open, although Leith Nursery is closed, as is Gylemuir Nursery.
The following 30 (of 87) primary schools will be open on Thursday in Edinburgh: Broomhouse, Broughton, Bruntsfield, Corstorphine, Craigentinny (Nursery closed), Craiglockhart, Dalry, Flora Stevenson, Forthview, Granton, Gylemuir (Nursery closed), Hermitage Park, James Gillespies (Nursery closed), Leith (Nursery closed), Leith Walk (Nursery closed), Lorne, Murrayburn (Nursery closed, language classes closed), Preston Street, Roseburn (Nursery closed), Sciennes, Sighthill (Nursery closed), St Mary's RC - Edinburgh, St Mary's RC - Leith, Stockbridge, Tollcross, Towerbank, Trinity, Victoria, Wardie.
All special schools with remain closed with the exception of the Panmure St Ann's service.
The following nurseries will be open on Thursday: Cowgate Under 5's Centre, Balgreen, Tynecastle, Calderglen, Balgreen, Stanwell, Cameron House and St Leonard 's.
Leith Academy will be open for all pupils (S1-S6) on Thursday. All other secondary schools will be open for 4th-6th year pupils on Thursday apart from Queensferry High which will be closed.
Earlier it was thought that Currie and Balerno High schools would have to close. It has been confirmed both schools will be open to S4-S6 pupils on Thursday.
Queen Margaret University has reopened its campus so students can use its facilities but there are no classes being held. Heriot Watt University's Edinburgh campus is closed.
Many private schools in Edinburgh have also been closed, including The Mary Erskine School and Stewart's Melville.
Edinburgh Napier University has reopened.
Jewel and Esk College has closed both its Edinburgh and Midlothian campuses to students. It will also be closed on Thursday.
All Fife's roads are currently open and "passable with extreme care", except the A90 approach to the Forth Road Bridge.
Lothian Buses said "some services are currently not operating their full route".
Edinburgh Castle has been closed for a third day due to "hazardous weather conditions" at the tourist attraction.
The city's zoo has been closed on Wednesday due to the snow.
Midlothian Snowsports Centre at Hillend is open on Wednesday until 2100 GMT. The access road has been cleared.
The Royal Botanical Gardens in Edinburgh was open on Wednesday.
Princes Mall in Edinburgh said it was running out of salt to grit the walkways on its roof and that it would be not be following its late Christmas shopping opening hours. It said it also might close early depending on the weather.
A Lothian and Borders Police spokesman said: "Most roads have experienced significant snow falls overnight.
"It is very unusual for the Forth Road Bridge to be closed and is an indication of the seriousness of the traffic problems being faced by motorists in the Lothian and Borders area.
"Side roads in particular will have had further builds up of snow and driving on them could be extremely challenging.
"Motorists are also urged to make sure their windows are properly cleared so that they have best possible vision and all snow accumulations are removed from their vehicles before they set out."
Bus queues in Edinburgh were also busier than usual on Wednesday as many commuters left their snow-covered cars at home and chose to travel by public transport.
Trains between Edinburgh Waverley and Bathgate have been suspended, and other routes were experiencing delays.
Trains between Edinburgh and Glasgow Queen Street have been reduced to a half-hourly service.
Postal services across the capital have also been affected by the heavy snowfall.
A Royal Mail spokesman said: "All our postmen and women in the Edinburgh area are working hard to keep the mail moving and are making deliveries and collections where it is safe and possible to do so."
Ch Insp David McCulloch, of Fife Constabulary, said: "Owing to the high levels of snow that fell overnight which led to treacherous driving conditions for early morning motorists, the Forth Road Bridge was closed.
"Unfortunately a number of drivers failed to react to the roadside signing identifying the bridge was shut and continued on past the exits.
"Consequently, a number of drivers chose to carry out u-turns or reversed considerable distances back up the carriageway into the face of oncoming vehicles.
"This is clearly a dangerous practise which could lead to serious consequences."