Highway congestion is a significant and growing problem in many urban and some rural areas. A major factor in the growing congestion is the failure of road capacity to keep pace with the growth in vehicle miles of travel. In the last 30 years, VMT has increased three times as fast as the rate of increase in highway mileage.
Congestion has two major causes.
First, there is recurring congestion due to normal and predictable surges in traffic volume. This congestion is unpredictable. The largest source of incident caused congestion is disabled vehicles. The remaining incidents are a miscellaneous grouping of events like debris or the road, law enforcement activities, and emergency road repairs. The time lost due to incidents can be substantial.