US investigations of 1.56 million Ford SUVs have ceased after an almost four-year investigation. The investigation was incited after allegations that 1.56 million Ford SUVs were at risk of rolling away. The case was dropped because of a low number of complaints, according to the National Highway Traffic Safety Administration. Models investigated were the 2002 to 2005 Ford Explorer and Mercury Mountaineer in addition to the 2003 to 2005 Lincoln Navigator.