Franchitti injured in flying wreck
Dario Franchitti prepares for practice for the Grand Prix of Baltimore on August 30, 2013 in Baltimore, Maryland
Franchitti's car went airborne and slammed into the safety fencing before coming to a halt in the middle of the street circuit track.
The Scotsman was stretchered off the track and taken by ambulance to the nearby Houston hospital.
Race officials said Franchitti was "awake and alert" but did not go into details on his injuries.
His team owner Chip Ganassi said Franchitti injured his ankle and back.
"He's talking," said Ganassi who rushed to the crash scene on a scooter. "His ankle is a little sore, his back is a little sore. He is going to be OK."
The three-car smash happened in one of the sharp turns and also involved Japan's Takuma Sato and E.J. Viso of Venezuela but they were both able to exit their cars and walk away.
Debris from the crash also flew over the top of the safety fencing, injury some spectators.
Race officials did not immediately provide details of those injuries.
The race was won by Australia's Will Power.
"Everybody hopes Dario is OK," said New Zealand driver Scott Dixon.