On-Line Estimation of Traffic Densities from Time-Series of Flow and Speed Data.

In this article a method is discussed for estimating the number of vehicles on a section of a roadway from speed and flow measurements at the entrance and exit points of the section. The method consists of obtaining rough estimates of this count at regular intervals, and then filtering random errors of these estimates by means of a sequential correction scheme. Emphasis is placed on economy in instrumentation and data processing. These methods have been adopted while estimating traffic densities, 1. An estimate of vehicle travel times is periodically obtained from the time series of speeds. 2. A rough estimate of the count is obtained from the inventory of car arrivals at the entrance of the section and the travel times of exiting cars. 3. The rough counts are adjusted by means of a "sequential estimator," to ensure the compatibility of successive counts with flow data. The identification of patterns of vehicles amounted to identification of individual vehicles, and hence a very accurate measurement of the number of cars between traps.