The B645 near St Neots was closed for more than four hours while investigators assessed the scene of a “serious” collision.
Cambridgeshire police and highways officials closed the road between the A1junction and the Moor Road junction with Great Staughton, at about 1pm, following a collision between a van and a motorcycle.
Police described the collision as serious, although details of any injuries have not yet been disclosed by officers.
Motorists were advised to avoid the area while investigations were carried out. The road re-opened again at about 5.30pm.