Police say the thief, who also took some signs, put road workers at risk.
The driver was travelling with three young children in the back of his vehicle, police say.
Police say they are examining a "number" of lines of inquiry.
Police put a cordon in place and say they are making inquiries.
The van driver is taken to hospital with serious injuries and the road is closed for several hours.
Emergency services including the air ambulance are called out and the A47 is closed for seven hours.
