Transport Supply, Demand and Travel Time
Within an urban area, transport supply (A) tends to be stable throughout the day, with the exception of public transit that adjusts its services (namely in terms of frequency) to cope with peak hours. Transport demand (T), on the other hand, varies considerably for several reasons, mainly linked with commuting. Typically, transport demand exceeds transport supply twice during the day (morning and afternoon peaks). The resulting congestion significantly increases travel time.