This indicator shows the extent to which vehicles are used, and must not be confused with availability. There are various measures of utilization; these include mileage or hours (kilometers per vehicle per period or operational hours/days per vehicle per period); analysis of days or hours of operation as a percentage of total available time; or the number of vehicles operated in a day as a percentage of the number available.
The most useful indicator is the number of vehicles used on revenue-earning service at a particular time (usually peak periods) as a percentage of the number of buses which are available for service at that time (i.e. excluding those undergoing maintenance or repair or not available for other reasons). In most city operations the morning peak is more concentrated, and therefore it is normally most useful to use this as the basis for calculation. Where there is no discernible peak, the maximum number of buses in service at any time during the day may be used. Utilization is sometimes expressed as a percentage of the total licensed or owned fleet, but this may give a false impression since a low level of utilization may be because insufficient buses are available, due for example to a large number of vehicles off the road for repairs, and not because the operations department is unable to find profitable work for the whole fleet.
Utilization normally varies between different times of the day (i.e. between peak and off-peak periods), different days of the week, and different times of the year. At peak times utilization on urban bus services should normally be between 95% and 100%. A small number of vehicles may be kept as spares in case of breakdown, but some operators schedule all available buses at peak periods, risking the need to cancel some journeys in the event of a breakdown. Poor utilization (as opposed to poor availability) may be due to a surplus of vehicles, inefficient scheduling, shortage of driving and/or conducting staff, or road or weather conditions which prevent the operation of some services.
A high level of utilization does not necessarily mean a high degree of efficiency or profitability. A fleet may be well utilized, but on services for which there is little demand and which consequently lose money. In addition, some buses may be used for very short periods during only one of the peaks, so that their revenue-earning capability is severely limited.