ABSTRACT
Recurrent congestion is caused by traffic bottlenecks formed when the traffic volume on
the freeway exceeds the freeway capacity. On the other hand, non-recurrent congestion may be caused by: (a) freeway incidents such as accidents, disabled vehicles, and spilled loads, (b) planned special events such as temporary maintenance and construction activities, and (c) unplanned events such as signal and detector malfunctions. Studies
have shown that freeway incidents cause approximately 60% of all urban freeway delays
in the United States (FHWA 1991).
