Calibration with empirically- derived origin-destination tables can go a long way toward earning stakeholder acceptance. In order to generate such tables, Skycomp aircraft circle study sites for 2 hours at a time, and photograph the assigned highway sections every 2 seconds during 40 minute sets. Later, photos are aligned to facilitate tracing; then a sample set of 150 to 200 vehicles per origin is traced to determine flow percentages to each destination. The resulting "true" OD tables are backed by tagged photo archives. (Recently, Skycomp completed a landmark OD study of Jersey City, NJ; this involved the synchronized operation of five circling airplanes photographing adjacent highway sections, so that vehicles could be traced for a total distance of up to five miles.)
Variations of this procedure include tracing the routes of commercial trucks through urban neighborhoods, in order to quantify driver compliance with truck route assignments.. Another variation created in 2007 involved modifying these procedures so that weaving speeds and lane changes could be measured for 35,000 vehicles at 10 sites around the United States. This was done as part of the research effort for the new weaving analysis procedures developed for the 2010 Highway Capacity Manual.
Roll cursor over clock stamps to see time-lapse effect. Digital "still" cameras provide much higher resolution than video, and thus provide for much larger survey areas than video cameras. This site was cropped from a much larger view.