Police had to close two lanes of the westbound carriageway , a mile short of Junction 17 so that debris from the accident could be cleared.
The increase in vehicles and the reduced carriageway made it difficult for them to move along the city roads.
The outside lane of the northbound carriageway was closed for half an hour while recovery teams cleared away the debris.
The smash happened at 11 am on Monday on the eastbound carriageway about half a mile from Junction 15.
Lane three of the eastbound carriageway was closed while police towed away the white van.
Road sweepers were drafted in to clear the carriageway while damaged vehicles were recovered.
One lane of the northbound carriageway was closed while emergency services dealt with the accident.
In a split second, the vehicle moved to the side of the road before hitting the kerb and going off the carriageway , smashing through a fence and down an embankment.
As things began moving more quickly, we passed the accident on the other side of the carriageway .
Suddenly the coach crossed the central reservation and collided with a public light bus travelling in the inner lane of the eastbound carriageway .