First have released an updated schedule after collisions and icy weather take their toll on transport links.
Plymouth was brought close to a standstill after a series of multi-car collisions.
Five crashes due to the icy conditions at the same time between Marsh Mills and Manadon closed the A38. Police say it will be closed until 1pm.
One man is in a critical condition.
A police spokesman said: "A number of vehicles had spun off the main road and onto the grass verges. At least one person was seriously injured as a result.
"The road has been closed at the Devonport and St Budeaux on slips. The Exeter bound carriageway is open from the Tamar Bridge but traffic is being directed off at St Budeaux.
"Diversions have been set up but there will be inevitable delays for the rush hours traffic. Officers at the scene believe that the freezing road conditions may be a contributory factor and are warning motorists to slow down when using any of the roads in the area.
"Further collisions on the approach to the scene are also adding to the congestion and motorists are advised delays journeys or avoid the area if possible."