The man was travelling north along State Highway 1 near Queens Gardens, Dunedin, at midnight last night when he crashed into the back of the truck, Acting Senior Sergeant Iain Notman said.
The driver's side of the car was wedged firmly under the left rear of the truck, trapping the man.
He was rushed to Dunedin Hospital by Hato Hone St John in a critical condition after being freed by Fire and Emergency New Zealand crews.
Norman said the man remained in hospital.
The road was closed for a scene examination and both vehicles were extensively damaged.
The man was on active charges for use of alcohol and had bail conditions not to drive a motor vehicle.
Police took a blood sample from him.
When officers searched the vehicle they found large amount of cash.
A resident who was first on the scene said the man was "speeding" down the one-way system before he crashed.
He said the man appeared to be conscious and talking when firefighters were working to free him before paramedics went over to assist.
