Levels of Service for Road Transportation

There are 6 levels of service:

(A) Free Flow Traffic. Individual users are practically unaffected by the presence of other vehicles on a road section. The choice of speed and the maneuverability are free. The level of comfort is excellent, as the driver needs minimal attention.
(B) Steady Traffic. The presence of other vehicles on the section begins to affect the behavior of individual drivers. The choice of the speed is free, but the maneuverability has somewhat decreased. The comfort is excellent, as the driver simply needs to keep an eye on nearby vehicles.
(C) Steady Traffic but Limited. The presence of other vehicles affects drivers. The choice of the speed is affected and maneuvering requires vigilance. The level of comfort decreases quickly at this level, because the driver has a growing impression of being caught between other vehicles.
(D) Steady Traffic at High Density. The speed and the maneuverability are severely reduced. Low level of comfort for the driver, as he must constantly avoid collisions with other vehicles. A slight increase of the traffic risks causing some operational problems and saturating the network.
(E) Traffic at Saturation. Low but uniform speed. Maneuverability is possible only under constraint for another vehicle. The user is frustrated.
(F) Congestion. Unstable speed with the formation of waiting lines at several points. Cycles of stop and departure with no apparent logic because created by the behavior of drivers. High level of vigilance is required for the user with practically no comfort.

The rate of traffic service is the maximal hourly rate that can cross a point or a road section according to road, traffic and control conditions. Therefore, each road infrastructure has five traffic rates of service (the F level is not used because unstable). Traffic reports also use color codes to illustrate traffic conditions such as green (levels A and B), yellow (levels C and D) and red (levels E and F).