The real time estimation of origin-destination flows in the presence of platoon dispersion

A number of procedures for the estimation in real time or origin-destination flows in junctions or small networks are reviewed. These are based on the assumption that the time taken by vehicles to traverse the junction or network is either small in relation to the chosen time interval or equal to some fixed number of time intervals. In reality, there will be a distribution of travel times that may span a number of time intervals. This paper proposes two ways to allow for this in the estimation of origin-destination flows. The first, appropriate if travel times are approximately geometrically distributed, makes use of the recurrence model of plantoon dispersion. The second makes no assumption about the form of the distribution of travel times, but in general requires the estimation of substantially more parameters. Simulation results for data containing geometrically distributed travel times suggests that fitting the correctly specified model produces better estimates of the turning proportions than does the conventional approach where travel times are restricted to a fixed number of time intervals.