Roadway networks are evaluated by comparing the traffic volumes along each facility to the facility's capacity. Roadway capacity is defined as the ability to accommodate traffic. Service flow volume is the level of traffic flow (vehicles per day) that can be accomodated at various levels of service.

Roadway Capacity Ratings

Level of Service A Free traffic flow (0% - 35% of capacity)
Level of Service B Stable traffic flow (35% - 50% of capacity)
Level of Service C Stable traffic flow (50% -62% of capacity)
Level of Service D High-density stable traffic flow (62% - 75% of capacity)
Level of Service E Capacity level traffic flow (75% - 100% of capacity)
Level of Service F Forced or breakdown traffic flow (.100% of capacity)