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The categories in Traffic Congestion Statistics are defined as follows.
| Category | Definition | |
| Population | ||
| Population (000) | Combination of U.S. Census Bureau estimates and the Federal Highway Administration's Highway Performance Monitoring System. | |
| Population rank | Out of 75 metro areas | |
| Population group | Size of meto area. Sml (small), Med (medium), Lr (large), Vlg (very large) | |
| Peak road travelers | Travelers who made a trip during the peak periods | |
| Urban area size in square miles | Size of area | |
| Freeway | ||
| Freeway daily vehicle-miles of travel (000) | The average daily traffic of a section of roadway multiplied by the length of that section of roadway | |
| Freeway lane miles | Total measure of all lanes | |
| Principal arterial streets daily vehicle-miles of travel (000) | The average daily traffic of a section of roadway multiplied by the length of that section of roadway | |
| Principal arterial streets lane-miles | Total measure of all lanes | |
| Cost Components, Delay, and Wasted Fuel | ||
| Value of time ($/hour) | The 2005 value of person time used in the report is $14.60 per hour based on the value of time, rather than the average or prevailing wage rate. | |
| Commercial Vehicle Operating Cost | Truck travel time is valued at $77.10 per hour for the purposes of estimating congestion cost. | |
| Fuel Costs | Statewide average fuel cost estimates were obtained from daily fuel price data published by the American Automobile Association (AAA). | |
| Total annual delay (1000 person-hours) | The value of lost time in passenger vehicles and the increased operating costs of commercial vehicles in congestion | |
| Travel time index | Ammount of additional time that is required to make a trip because of congested conditons on the roadways. Includes recurring and incident conditions. | |
| % of Daily Travel During Congested Times | 6:00 - 9:30 am and 3:30 - 7:00 pm | |
| Operational Treatments | Freeway incident management, freeway ramp metering, arterial street signal coordination, arterial street access management and high-occupancy vehicle lanes. | |
| Public Transportation | Regular route service from all public transportation providers in an urban area. | |
| Congested Travel | ||
| Congested System | ||
| Annual Roadway Deficit (lane-miles) to maintain congestion level | The number of lane-miles that an urban area is short of to offset traffic growth. | |
| Excess Fuel Consumed | Increased fuel consumption due to travel in congested conditions rather than free-flow conditions. | |
| Congestion Cost | Value of travel time delay (estimated at $14.60 per hour of person travel and $77.10 per hour of truck time) and excess fuel consumption (estimated using state average cost per gallon). 2005 values include the effects of operational treatments. | |
| Transit or Carpool Riders needed to maintain congestion level | The number of transit trips needed to maintain the same congestion level | |