A male cyclist suffered serious injuries following a collision on the A41 this morning (Thursday, July 7).
Police were called at 10.34am to the A41 southbound just before the Berkhamsted exit sliproad.
The bypass was then closed in both directions to allow the air ambulance to land.
The northbound side of the carriageway has now been reopened but the southbound stretch remains closed from the Tring junction.
The cyclist has been taken to hospital for treatment. Though his injuries are serious, they are not thought to be life-threatening.
Police are still at the scene and the southbound carriageway is still closed.