A set percentage or number of vehicles based on fleet size held in reserve to be used to replace vehicles that are out of service. FTA guidelines for spare ratios are 2 vehicles for fleets of up to 10 vehicles; 20% for vehicle fleets of 11 and over. Spare ratios must include vehicles that are wheelchair-lift accessible. The FTA has not established a requirement for rail car spare ratios, but it does require the operator to develop a fleet management plan which details operating policies, peak requirements, and maintenance and procurement schedules.