| Level of Service |
Interpretation |
Nominal Range to Volume-to-Capacity Ratio |
|---|---|---|
| A |
Low volumes; primarily free-flow operations.
Density is low, and vehicles can freely maneuver within the traffic stream.
Drivers can maintain their desired speeds with little or no delay. |
0.00 - 0.60 |
| B |
Stable flow with potential for some restriction
of operating speeds due to traffic conditions. Maneuvering is only slightly
restricted. The stopped delays are not bothersome, and drives are not subject
to appreciable tension. |
0.61 - 0.70 |
| C |
Stable operations; however, the ability
to maneuver is more restricted by the increase in traffic volumes. Relatively
satisfactory operating speeds prevail, but adverse signal coordination or
longer queues cause delays. |
0.71 - 0.80 |
| D |
Approaching unstable traffic flow, where small increases in volume could cause substantial delays. Most drivers are restricted in their ability to maneuver and in their selection of travel speeds. Comfort and convenience are low but tolerable. | 0.81 - 0.90 |
| E |
Operations characterized by significant
approach delays and average travel speeds of one-half to one-third the free-flow
speed. Flow is unstable and potential for stoppages of brief duration. High
signal density, extensive queuing, or progression/timing are the typical
causes of the delays. |
0.91 - 1.00 |
| F |
Forced-flow operations with high approach
delays at critical signalized intersections. Speeds are reduced substantially,
and stoppages may occur for short or long periods of time because of downstream
congestion. |
1.010+ |