Percentage of lost kilometers
Lost kilometers are scheduled kilometers which are not operated for any reason. Lost kilometers as a percentage of scheduled kilometers is an indicator of overall service reliability in an operation in which buses are run to schedule. Ideally the figure should be 0% but this is rarely achieved. A reasonable figure for urban services in ideal operating conditions would be between 0.5% and 2.5%; a figure above 5% should give cause for concern. In many developing countries, however, the figure is much higher than this, often between 20% and 30% or even higher, due not only to poor mechanical reliability and organizational weaknesses, but also to problems of unpredictable traffic congestion which cannot be provided for in the schedules.

Another measure is to calculate lost kilometers as a percentage of total kilometers operated, but this may be misleading, particularly where a high proportion of unscheduled kilometers is operated. It is not always easy to record lost kilometers accurately: sometimes it is easier to record lost trips rather than lost kilometers, but this figure is distorted by vehicles which break down during the course of a trip, and there will normally be wide variations in trip lengths between one route and another.