The OKI region’s quality of life and economic competitiveness are closely related to the degree to which the transportation system is able to provide an acceptable level of mobility.  Congestion is the level at which transportation system performance is no longer acceptable due to traffic interference.  This traffic interference may be recurring or non-recurring congestion.  Recurring congestion is caused by consistently excessive travel demand as compared to available roadway capacity.  Sometimes, poor signal timings, poor access management and roadway geometric deficiencies contribute to reduced capacity.  Non-recurring congestion occurs due to traffic incidents, adverse weather or road construction.  The relative severity of travel congestion is measured by travel time, speed and the calculated measure called travel time index.