The present paper proposes methodological and technological improvements in order to enrich the traditional moving observer method by direct measurement of the speed and length of each vehicle by the observer, while the former moves in one lane and the latter in an adjacent lane. This is realized using two laser detectors located on the observer’s vehicle and acting as a mobile double presence-type detector. In addition, the observer’s vehicle is equipped with a DGPS-based system that provides absolute positioning of all events during these meetings with the recorded vehicles (activation and deactivation of detectors) as well as their timing. These capabilities provide sufficient information for determining the prevailing speed distribution in non-congested conditions for short time periods of measurements (i.e. few minutes). The distribution contributes to reliable estimates of average flow and mean space speed for a relatively long highway section. The method proves its value, when fixed detector and moving measurements are combined; then the exact space speed distribution could be determined, and the exact mean space speed could be calculated. Finally, the method has the capability to follow the traffic stream characteristics along successive sections recognizing variations in the prevailing traffic conditions in non-congested and/or congested environment.
Keywords: moving observer method; differential Global Positioning System; Laser detectors; measurement of vehicle speed; measurement of vehicle length; instantaneous speed distribution