A typical daily urban commuting profile involves with
two peak hours, morning and afternoon, which are recurring on a regular
basis (on weekdays). Under normal circumstances, the transport system
has a fixed capacity which remains constant throughout the day. This
capacity is an outcome of road characteristics such as the
number of lanes and operational constraints such as the mix of
vehicles and speed limits. Congestion
occurs when the amount of traffic exceeds the design capacity, which
is commonly the place during the morning and the afternoon peak
hours. A common issue is which level of capacity should be
provided considering the daily distribution of traffic. A
capacity which is too high would be expensive to provide
although it would offer the benefits of limited congestion.
Limited capacity would be linked with enduring congestion and
negative economic externalities.