The number of vehicles in the queue at the start of green is calculated in TRAFFIX™ using the two optional methods. One method is referred to as the Australian Method and it uses the following formula developed by Akçelik.
Where:
c = Cycle length in seconds
u = g/c (no units)
No = Number of vehicles remaining after green ends.
q = Capacity in vehicles per second = s*g/c
t = Flow period in seconds (default = 900)
x = Degree of saturation = (v*c)/(g*s)
v = Approach volume in vehicles per second (vps)
xo = a + b*s*g
a = 0 for HCM, 0.67 Australian, 0 for Others.
b = 0 for HCM, 1/600 Australian, 0 for Others.
s = Saturation flow rate (vehicles/second)
g = Effective green in seconds (note s*g = capacity per cycle)
m = function of g/c, arrival type, signal control type for 1994 HCM method
(see Table 9-13, pg. 9-28, 1994 HCM);
= 12 for Australian method,
= 4 for 1985 HCM and other methods.
n = 2 for HCM, 0 for Australian and Canadian, -1 for Transyt8.
This is the mean queue for the lane group and represents the deterministic maximum back of queue after the start of green, plus a random component to account for random fluctuations in the arrivals during the red signal interval. It is not, however, the 95-percentile queue. The user needs to exercise engineering judgment in interpreting and using these queue values. The user may find that this method tends to over-estimate the actual mean queues.
This method is selected from the Options...Global Data...Parameters dialog box. Note that there is a field provided here for the average vehicle length, but this is not used by the Australian method.
To obtain an estimate of the needed queue storage length for design purposes using this method. The Queue (in vehicles per lane group) reported by TRAFFIX should be:
Multiplied by a user-determined statistical factor to account for random variations in arrival rates throughout the peak hour,
Multiplied by the average storage length per vehicle, and
Divided by the number of lanes.
TRAFFIX does not calculate an average stop rate, however the user may use the following equation to calculate stops per vehicle:
Total Stops per second = [volume (vps)] x [average stop rate]