LEVEL-OF-SERVICE CONCEPT
The Highway Capacity Manual (HCM), produced by the Transportation Research Board [2016], is a synthesis of the state of the art in methodologies for quantifying traffic operational performance and capacity utilization (congestion level) for a variety of transportation facilities. One of the foundations of the HCM is the concept of level of service (LOS). The LOS represents a qualitative ranking of the traffic operational conditions experienced by users of a facility under specified roadway, traffic, and traffic control (if present) conditions. Current practice designates six levels of service ranging from A to F, with LOS A representing the best operating conditions and LOS F the worst.
A number of operational performance measures, such as speed, flow, and density, can be measured or calculated for any transportation facility. To apply the LOS concept to traffic analysis, it is necessary to select a performance measure that is representative of how motorists actually perceive the quality of service they are receiving on a facility. Motorists tend to evaluate their received quality of service in terms of factors such as speed and travel time, freedom to maneuver, traffic interruptions, and comfort and convenience. Thus, it is important to select a measure that encompasses some or all of these factors. The performance measure that is selected for LOS analysis for a particular transportation facility is referred to as the service measure.
