HOUSTON (AP) — Police say a woman suspected of stealing an unoccupied ambulance parked at a Houston hospital has been seriously hurt after rolling the emergency vehicle.

Houston police are trying to determine why the woman got into the Acute Medical Services ambulance early Monday and drove away from Ben Taub Hospital. Police spokeswoman Jodi Silva says investigators don't believe the woman was a patient.

Silva says an ambulance employee says the keys were in the vehicle, parked in a loading and unloading area. The ambulance wrecked on a Houston freeway about 45 minutes after being reported stolen.

Silva says the suspect, who was trapped under the vehicle, suffered severe injuries and was transported back to Ben Taub Hospital.

Silva says the woman is expected to face charges. Her name wasn't immediately released.