Highlights • Locations of initial dispersion and higher dispersion regions are identified. • Speed variability measures and platoon characterizing variables are analysed. • Initial and higher platoon dispersion occurred at 180 m and 360 m respectively. • Critical inter arrival time at these locations are 2.8–3.2 s and 3.2– 3.6 s.

Abstract Vehicles released from the traffic signal travel along the arterial in platoons. These tend to disburse as they proceed through the corridor. The present study uses various measures which quantify speed variability to determine regions where initial dispersion and higher dispersion occur on signalized urban arterials under heterogeneous traffic conditions. Video graphic survey technique was used to collect the traffic data. Data was collected up to 420 m and each platoon was analysed at every 30 m interval. The analyses identified the pattern of dispersion of platoons of vehicles along the downstream of traffic signals at three different volume levels. On the basis of the fluctuations depicted by the measures which quantify speed variability namely profiles of speed, standard deviation, relative standard deviation, relative speed difference and platoon characterizing variables, the regions where in initial and higher platoon dispersion occurred along the downstream of traffic signals were identified as 180 m and 360 m respectively. It is found that at the critical inter arrival time range of 2.8 s–3.2 s initial dispersion happens and at the range of 3.2–3.6 s higher dispersion occurs under heterogeneous traffic conditions. This research work provides better understanding of platoon dispersion phenomenon under heterogeneous traffic conditions in order to improve signal coordination and to enhance traffic flow.