Level of Service (LOS) F in transportation and traffic engineering represents the lowest quality of traffic flow, characterized by severely congested conditions. It is marked by traffic flow breakdown, with features including:
- Oversaturated Flow: Traffic exceeds the capacity of the roadway, leading to a complete breakdown in flow. This level is associated with gridlock conditions where traffic volumes are higher than what the road can accommodate.
- Very Low Speeds and Stop-and-Go Traffic: Vehicles move at very low speeds, often in a stop-and-go fashion. The movement is frequently halted, and the rate of progress is extremely slow.
- High Density and Long Delays: The density of vehicles is very high, resulting in prolonged delays. Vehicles may be stationary for significant periods, especially at intersections or congested stretches of the road.
- Poor Operational Conditions: The driving experience is characterized by frustration and discomfort due to the excessive congestion and lack of mobility.
- Lowest Level of Comfort and Convenience: LOS F offers the lowest level of comfort and convenience for road users. The high density and frequent stopping create a stressful and inefficient driving environment. LOS F is considered unacceptable in most planning and design scenarios and is typically used as an indicator that significant improvements or interventions are needed to alleviate congestion. This level of service is a clear sign of inadequate infrastructure for the existing traffic demand, necessitating either capacity enhancements or demand management strategies to improve traffic conditions.
LOS in parking design
For a parking facility, LOS F usually shows up as queues backing out of the entrance onto the street, or exit lines that take many minutes to clear after an event. Typical causes are too few lanes, slow transactions at the gates, or a peak larger than the design assumed. Remedies include added lanes, faster credentials such as license plate recognition or prepaid exits, and spreading the peak with pricing. See PARCS and license plate recognition.