The A1 southbound in North Yorkshire was closed due to a crash that left one car overturned.
The road was closed from J51 Leeming and J50 Baldersby/Ripon.
North Yorkshire Police had carried out collision investigation work and asked drivers to avoid the area saying that the road was expected to remain closed for "some time."
The fire and rescue service were also in attendance.
Two air ambulances had arrived and left the scene by about 10am.
Highways England confirmed at about 12pm that the latest estimate for the road re-opening is now approximately 3 hours.
At about 2pm they issued this update on Twitter. It said: "UPDATE #A1M J51 #Leeming to J50 # Baldersby/Ripon police have concluded their investigations, the road should be opening shortly, we will keep you updated. Thanks for your patience."
At 2.20pm Highways England confirmed that the delays were spanning 4 miles back to J25.
Average speeds on approach were 12pm.