A five-car crash has closed part of the A41 near Hunton Bridge.
Emergency services were called to the road near Langleybury Cricket Club shortly before 3pm to reports that five vehicles had collided.
Firefighters from Kings Langley and Garston freed one motorist who was trapped in their car.
The crash has blocked both carriageways and police have put a closure at Langleybury lights crossing while they await recovery of the cars.
Paramedics treated four patients at the scene and a woman in her 50s has been taken to Watford General Hospital with neck injuries. Her condition is not thought to be life-threatening.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here