spare ratio

A spare ratio or spares ratio is the percentage of unused vehicles operated by a public transport operator during peak service periods. It is calculated as a simple percentage of the total fleet size.{{cite web |last=MacKechnie |first=Christopher |date=May 31, 2016 |title=Transit 101: The Spare Ratio |url=http://publictransport.about.com/od/Transit_Vehicles/a/Transit-101-The-Spare-Ratio.htm |publisher=About.com |accessdate=August 1, 2016}}

In the United States, the Federal Transit Administration (FTA) sets a 20 percent guideline for the spare ratio in a fleet of at least 50 vehicles.{{cite web |date=August 27, 2012 |title=FTA Circular 9030.1C: Urbanized Area Formula Program: Program Guidance and Application Instructions |page=5 |url=https://www.transit.dot.gov/regulations-and-guidance/fta-circulars/circular-urbanized-area-formula-program-program-guidance-and |publisher=Federal Transit Administration |accessdate=August 1, 2016}}