Level of service is a grading system for amount of congestion, using the letter A to represent the least amount of congestion and F to refer to the greatest amount. The appropriate degree of congestion (that is, the level of service) to be used in planning and designing highway improvements is determined by considering a variety of factors. These factors include the desires of the motorists, adjacent land use type and development intensity, environmental factors, and aesthetic and historic values. Peak-Hour Level of Service

Once an appropriate design speed has been selected, the other basic defining elements of the highway (i.e., the number of lines and the basic configuration of junctions with other highway facilities) can be determined through application of the concept of acceptable peakhour level of service. Level of service is a grading system for amount of congestion, using the letter A to represent the least amount of congestion and F to refer to the greatest amount. For a comprehensive treatment of this topic, refer to the Highway Capacity Manual. Table 4.3 presents a brief description of the operating characteristics associated with each level of service.

The appropriate degree of congestion (that is, the level of service) to be used in planning and designing highway improvements is determined by considering a variety of factors. These factors include the desires of the motorists, adjacent land use type and development intensity, environmental factors, and aesthetic and historic values. The factors must be weighed against the financial resources available to satisfy the motorists' desires. Table 4.4 presents the relationship between highway type and location and the level of service appropriate for design, suggested by the AASHTO Green Book. Taking into consideration specific traffic and environmental conditions, the responsible highway agency should attempt to provide a reasonable and costeffective level of service.

While the Highway Capacity Manual provides the analytical basis for design calculations and decisions, judgment must be used in the selection of the appropriate level of service for the facility under study. Once a level of service has been selected, all elements of the roadway should be designed consistently to that level. For example, along recreational routes subject to widely varying traffic demands according to the time of year or in response to environmental or land use considerations, the designer may conclude that the selection of a level of service that is lower than what is usually recommended may be appropriate. The selection of the desired level of service for a facility must be weighed carefully, because the facility's overall adequacy depends on this decision.