Volume (sometimes called ‘flow’ or ‘flow rate’ and here designated by the symbol ‘q’) is the number of vehicles per unit time passing a given point on a road. Volume may relate to a lane, a carriageway or a road and, in the case of a road, may include traffic in either one or both directions. In traffic flow analysis, a volume usually relates to only one direction of flow.
The unit of time used in relation to a volume may vary according to the application. Volumes expressed as vehicles per second (veh/s) or vehicles per hour (veh/h) are typically used in traffic flow analysis, while daily or annual volumes may be appropriate in other contexts, such as analyses of traffic growth over time.