Freeway operating conditions are typically evaluated using the level of service (LOS) concept, which is defined according to the macroscopic traffic parameter, density. Although traffic density may provide general estimates of current traffic conditions, this parameter generally fails to communicate the variability in the quality of traffic flow experienced by individual drivers. This variability may be caused by factors that are not effectively being captured by density, such as travel lane, vehicle position within a platoon, characteristics of roadway geometry, etc. This paper investigates the variability of traffic flow quality as indicated by measurements of speed and acceleration noise (standard deviation of acceleration) using field data obtained from instrumented vehicles equipped with global positioning system (GPS) devices. The microscopic measures observed from individual vehicles are compared with density-based LOS, which are calculated with data from the Atlanta, GA traffic monitoring system. This comparison reveals that under the same LOS condition, drivers may experience significant differences in the quality of traffic flow. In addition, the comparison indicates that drivers under different density based LOS conditions may experience the same level of traffic flow quality. The variability generally becomes larger as traffic conditions worsen.
Abstract