On urban arterials in China traffic presents a mixed flow feature because of the large percentage of buses. This affects the applicability of traditional platoon dispersion models which generally only suitable for homogeneous traffic flow. Based on field observation, this paper proposes a mixed platoon dispersion model (MPDM) to macroscopically simulate the platoon dispersion process along the road segment between two successive signalized intersections from the density view. To capture the heterogeneity in platoon speeds, truncated mixed Gaussian distribution (TMGD) is adopted to fit the field collected speed data, and expectation maximization (EM) algorithm is employed for the estimation of the distribution parameters. A piecewise platoon density function is developed to examine the platoon dispersion characteristics. By applying this density function, the formulation of the expected number of vehicles in the front of the platoon that have passed and the expected number of vehicles at the rear of the platoon that have not passed a downstream intersection, as well as the downstream arriving flow function are presented. Numerical calculation for signal coordination verifies the effectiveness of the proposed MPDM.
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