The A14 has been closed westbound following a serious multi-vehicle accident.
The crash happened at Bar Hill near Cambridge at about 10.30am, involving a number of lorries.
The road has completely shut on the westbound carriageway, leaving a long diversion for motorists trying to get north from the M11. The diversion takes people along the A428.
A spokesman for Cambridgeshire police said: " At 10.36am Police were called to a Road Traffic Collision on the A14 at Bar Hill.
"One Car and multiple lorries are involved. There are 4 lorries believed to be involved.
"There is currently 1 lane open and officers are hoping to have a second lane opened shortly."