Vehicles are replaced according to a schedule, the majority (sedans, subcompacts, small trucks and small SUVs) are replaced at 10 years, or 100,000 miles. Larger vehicles, trucks, and large SUVs are replaced at 10 years or 120,000 miles. All vehicles for a year are replaced at approximately the same time; it is either done through an annual state buy or through an inter-agency buy. The vehicles that are replaced are then sold as surplus.