American Institute of Certified Planners (AICP) Practice Exam

In terms of traffic flow, what is indicated by Level of Service D?

1. Free and clear traffic movement

2. High delays and queuing at traffic signals

3. Unstable flow with wait times increasing

4. Heavy congestion with frequent stops

The correct answer is: Unstable flow with wait times increasing

Level of Service D indicates unstable flow in traffic conditions where the movement is becoming more congested. At this level, vehicles are able to move but with increased delays, leading to wait times that fluctuate and can be unpredictable. Drivers may experience a lack of freedom to maneuver due to the proximity of vehicles, resulting in a scenario where the flow is not smooth. While there may be some traffic movement, the situation can lead to growing frustration for drivers as conditions deteriorate, and delays at key points such as traffic signals become more pronounced. In contrast, the other conditions described in the choices do not fit the essence of Level of Service D, which is characterized by instability rather than complete congestion or clear movement.