Another method for calculating vehicle queues is referred to as the Design Queue method and is selected by default. This method computes the mean maximum queue length at the start of the green, and then computes the mean maximum back of the queue some time after the start of the green, and then estimates the 95th percentile design queue by multiplying this mean by a factor of two. If the user feels a factor of two is inappropriate for observed conditions the resulting queue estimates can be used with adjustments by the user. The queue calculation equations for this method are as follows:
L = the 95 th percentile design storage length
Qb = Mean Maximum Back of Queue in a lane (some time after the start of green):
Qm = Mean Maximum Queue Length (at start of green):
V = volume per hour
C = cycle length
g = green time
d = average vehicle length
N = number of lanes
F = free-flow speed on the street (feet per second or meters per second);
default: 50 fps (15.24mps)
3600 = seconds per hour
Source: Australian Road Research Report 123, 1981. Page 26.
The results are queue lengths in terms of total vehicles by lane group. If the user wants stacking distance per lane, these queues need to be multiplied by an average vehicle length and divided by the number of lanes in the lane group.
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 to be used. This is needed for the Design Queue calculation method, but the queue lengths are still reported in terms of vehicles (not distance).