Experimental study of short range interactions in vehicular traffic

Single vehicle data obtained from magnetic loops on an expressway allowed us to measure velocity correlations and velocity differences between non--neighbor vehicles on the same lane, showing some strong correlations even for platoons of 7 or 8 vehicles. The corresponding time headway distribution for non--neighbor vehicles is also presented. We were also able to get some informations about inter--lane structures, through crossed time headway distributions. It should be noticed that these last results on crossed time headways are meaningful only because the subset of data we used corresponds to a unique stationary traffic state -- and still contains a large amount of data, with a large fraction of short time headways. The link with passing maneuvers is discussed.