CEE 764 – Fall 2010 Topic 5 Platoon and Dispersion

CEE 764 – Fall 2010 TRANSYT-7F MODEL  TRANSYT is a computer traffic flow and signal timing model, originally developed in UK.  TRANSYT-7F is a U.S. version of the TRANSYT model, developed at U of Florida (Ken Courage)  TRANSYT-7F has an optimization component and a simulation component.  The simulation component is considered as a macroscopic traffic simulation, where vehicles are analyzed as groups.  One of the well known elements about TRANSYT-7F’s traffic flow model is the Platoon Dispersion model.

CEE 764 – Fall 2010 WHY MODEL PLATOON DISPERSION?  Platoons originated at traffic signals disperse over time and space.  Platoon dispersion creates non-uniform vehicle arrivals at the downstream signal.  Non-uniform vehicle arrivals affect the calculation of vehicle delays at signalized intersections.  Effectiveness of signal timing and progression diminishes when platoons are fully dispersed (e.g., due to long signal spacing).

CEE 764 – Fall 2010 PLATOON DISPERSION MODEL  For each time interval (step), t, the arrival flow at the downstream stopline (ignoring the presence of a queue) is found by solving the recursive equation

CEE 764 – Fall 2010 PLATOON DISPERSION Flow rate at interval t, q t % Saturation Time, sec Start Green Flow rate at interval t + T, Q (T+t) Time, sec % Saturation T = 0.8 * T’

CEE 764 – Fall 2010 CLOSED-FORM PLATOON DISPERSION MODEL Time Flow rate, vph 0tqtq tgtg C s v

CEE 764 – Fall 2010 CLOSED-FORM PLATOON DISPERSION MODEL (1~t q ) For 1~t q with s flow

CEE 764 – Fall 2010 CLOSED-FORM PLATOON DISPERSION MODEL (0~t q ) (1) (2) (1) – (2)

CEE 764 – Fall 2010 CLOSED-FORM PLATOON DISPERSION MODEL (1~t q ) For 1~t q with s flow Maximum flow downstream occurs at T+t q with upstream s flow

CEE 764 – Fall 2010 BEYOND (1~t q ) s no longer exists, but zero flow upstream t = t q +1 ~ ∞ From the original equation: This is mainly to disperse the remaining flow, Q s,max. Upstream flow is zero The same procedure for the non-platoon flow The final will be the sum of the two

CEE 764 – Fall 2010 EXAMPLE  Vehicles discharge from an upstream signalized intersection at the following flow profile. Predict the traffic flow profile at 880 ft downstream, assuming free-flow speed of 30 mph, α = 0.35; β = 0.8. Use time step = 1 sec/step Time Flow rate, vph C=60 sec

CEE 764 – Fall 2010