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, mainly because of commuting patterns that are characterized by morning and afternoon periods of peak activity. During these periods transport demand usually exceeds transport supply with the resulting congestion significantly increasing travel time. The same journey can this take more of less time depending on the time of the day and the prevailing supply / demand relations.