On the M1, police receive reports of a lorry drifting across busy lanes. As officers get on its tail, the 40-ton vehicle swerves out of control, almost smashing into a queue of traffic on a slip road. A HGV mysteriously loses control on a dual carriageway and veers off the road, crashing head-first into a ditch. On the M1, a lorry pile-up brings officers racing to the scene.