Live horse racing is returning to Virginia after a 5-year absence. Colonial Downs, which has been dormant since 2014, is launching a 15-day race meeting beginning on Thursday. The live racing follows an infusion of revenue from historical horse racing machines, which function like slot machines but technically base their payouts on the results of old horse races. The Colonial Downs Group, which owns the racetrack, also operates the machines at three locations throughout the state under the name Rosie’s Gaming Emporium. In June, gamblers wagered more than $88 million at the machines. Wagering at the Colonial Downs site alone grew 10 percent from May to June. Admission to the New Kent County racetrack, about halfway between Richmond and Williamsburg, will be free throughout the meet. Colonial Downs has an off-track betting site located at the Dutch Inn, Collinsville.