CE 572 Applied Traffic Operations - Spring 2002

Exercise 03 - Effect of Headway Distribution on Capacity

Consider a TWSC intersection in which the minor street through movement experiences a range of major street (conflicting) flow rates that vary from 100 veh/ hr to 1500 veh/hr.  Assume a critical gap of 6.5 seconds and a follow up time of 4.0 seconds.  We want to determine the effect of different arrival patterns in the major street flow on the capacity of the minor street flow.

Case 1.  Random arrivals.  Here the HCM procedure can be used to compute the range of minor street capacity as a function of the variation of major street (conflicting) flow as given above.

Case 2. Uniform arrivals.  Here we assume that there is a constant headway in the major street flow.  For example, if the major street flow is 600 veh/hr, there will be a constant headway of 6 seconds between each vehicle.

Case 3. Platooned arrivals.  Here we assume that there is some upstream phenomenon, such as a traffic signal, that is filtering the flows that arrive at the downstream TWSC intersection.  Let's assume a cycle length at this signal of 100 seconds and a platoon headway of 2 sec/vehicle.

What is the capacity flow for each case described above for the range of major street flow rates given above (100 veh/hr to 1200 veh/hr)?