Hundreds of motorists were stranded on the A14 when a van carrying gas canisters caught fire.
The accident happened during rush hour on Wednesday between junctions 36 and 37 and caused huge tailbacks.
Motorists were given bottled water by police as diverted traffic also clogged up the A142, the A10 and the A11.
Bomb disposal officers had to be called in to monitor the gas cylinders after experts said firefighters could not safely reach them.
The A14 stretch will remain closed until about 1330 BST on Thursday.
A Suffolk Fire Service spokeswoman said: "On the advice of the British Oxygen Company the gas cylinders are unstable and need 24 hours to cool."
The van crashed about 100m from Rowley Mile service station near Newmarket - on the Cambridgeshire/Suffolk border - which was then evacuated.
A diversion route on the A142 was also blocked when a bus broke down.
The army team will remain on site to monitor the acetylene cylinders.
The order was given after it became clear firefighters could not safely approach the vehicle.
The Red Cross opened its centre in Newmarket to help people who were left stranded.
Ch Insp Neil Atwell from Suffolk police said: "Officers are working as fast as they can to dissolve the jams and hand out water supplies to people who have been trapped in the heat."