The man crashed his Nissan Qashqai on the M90 Friarton Bridge heading northbound towards Dundee and Aberdeen at around 11.25pm on Saturday night.
Police, paramedics and the fire brigade attended but found no sign of the man.
An "extensive" search operation was launched, with the driver found almost three hours later at 2.20am.
Police say he had suffered a "serious" head injury and he was rushed to Dundee's Ninewells Hospital for treatment. One lane of the bridge was closed for several hours while the investigation took place. A spokesman for Police Scotland's Tayside Division said: "About 11.25pm, Saturday 19th April 2014 a road traffic collision involving one vehicle, a Nissan Qashqai, occurred on the northbound carriageway on the Friarton Bridge at Perth. Officers from Police Scotland attended and failed to trace the driver of the vehicle. An extensive search was carried out by police officers and members of the Scottish Fire and Rescue Service and the Scottish Ambulance Service. About 2.20am the driver was traced nearby having suffered a serious head injury. He has been conveyed by ambulance to Ninewells Hospital in Dundee for treatment. His condition at present is unknown but not believed to be life threatening."