A major collision closed the Aston Clinton bypass and was set to cause rush hour chaos on Wednesday evening.
The road was closed after the incident causing long delays for rush hour motorists.
A Transport for Bucks tweet said: "#AstonClinton bypass closed at #Woodlands southbound following major road traffic collision. Please retweet ahead of rush hour."
A South Central Ambulance Service spokesman said: "We have sent two rapid response vehicles, an ambulance officer to the scene of a serious accident on the A41 at Aston Clinton following an emergency 999 call received at 2.32pm."
This newspaper understands that the collision involved a cyclist and a vehicle, but we are working to verify further details at this stage.
Thames Valley Police Roads Policing said that a scene investigation would take place, the road would remain closed during the busy period - and was likely to be reopened at 5.30pm.
More to follow as we get it.