U.S. officials have closed an investigation into allegations that three Ford SUVs can roll away when the transmissions are in park.

The National Highway Traffic Safety Administration says the probe involved about 1.5 million Ford Explorer, Mercury Mountaineer and Lincoln Aviator SUVs.

The agency determined that failure rates weren't high enough to order a recall. The probe began in April 2009 and was closed last month. The safety agency found 36 complaints including 14 crashes and six injuries.

Investigators found that the park gear in the transmission failed only 4.4 times per 100,000 vehicles. A system that prevents the car from being shifted into gear unless the driver's foot is on the brake failed only 3.4 times per 100,000 SUVs.

- Associated Press