The Met Office has extended its yellow alert for snow until 6am on Tuesday, with icy conditions also likely to affect many roads throughout the morning.
Heavy snow resulted in very difficult driving conditions on Monday evening, with delays of up to two hours reported, particularly in Co Down and Co Antrim.
The Roads Service said salting and ploughing operations were underway from early afternoon "on a continual basis in the affected areas".
"The operations were affected by the intensity of the snow, the volume of very slow moving traffic, and in places by a number of broken down or abandoned vehicles," a spokesman explained.
Areas particularly affected included Belfast, the Greater Lisburn area, the Templepatrick hills, Comber, Saintfield, Ballygowan, Hillsborough, Carryduff, the Castlereagh hills, Dundonald, Holywood, Moira, Ballynahinch, Dromore, Dromara, Banbridge, Rathfriland and Castlewellan.
The Church Road in Holywood and the B27 Moyad Road over Spelga remained closed on Monday night. The Shane's Hill Road between Larne and Ballymena was closed due to snow and stranded vehicles, police said.
Earlier two breakdowns on the M1 westbound at Stockmans Lane reduced the motorway to just two lanes.
Motorists leaving Belfast queued from Broadway, and the delays affected Stockmans Lane towards the M1 and Balmoral Avenue heading towards Stockmans Lane.
Later police closed the M1 westbound at Stockmans Lane and Blacks Road because of a stranded lorry. It has since reopened.
"Salting and ploughing operations will continue as necessary overnight with the aim of having the network clear for morning traffic," the Roads Service said.
"Motorists are advised to exercise caution when travelling overnight and in the morning, particularly when driving on untreated roads."
Belfast International Airport remained "open and operational" on Monday.
"However adverse weather across the UK could affect some flights", a spokesperson said.
A small number of flights were cancelled to and from Belfast City Airport on Monday morning. The airport also put any delays down to a knock-on effect from the disrupted schedule.
All passengers are advised to contact their individual airline for the latest flight information.
A number of schools were closed on Monday, particularly in the North Eastern Education and Library Board area.
McKinney Primary School in Dundrod, Co Antrim will be closed on Tuesday.