An intersection is located in an area with no slope. Due to the heavy traffic observed in the
intersection, especially during the morning and evening peak hours, the municipality has decided
to signalize the intersection. Two phases are considered for the signal, where phase 1 is dedicated
to the major street on the East-West bound (including through, right turn, and left turn
movements) and phase 2 is dedicated to the minor street on the North-South bound (including
through, right turn, and left turn movements). The street widths in the E-W and N-S directions
are respectively measured at 50 and 30 feet (L1 = 50 and L2 = 30), as shown in the figure below.
The speed and time headway values of two samples of vehicles are measured; one sample in the
E-W direction and the other sample in the N-S direction. In addition, the speed of a pedestrian
sample is measured. The signal should be designed for the 80th percentile speed of the two vehicle
samples and the 50th percentile speed of the pedestrian sample. The values can be found in the
table below. It is also observed that the length of a typical vehicle is 16 ft.
(a) Design the two-phase signal only for the vehicles for a cycle length equal to 120 seconds, and
minimum green interval of 25 seconds for the minor street (tr = 1 s). Draw the two phases.
(b) Design the signal by including the pedestrian. Draw the phases.
(c) Calculate the intersection capacity in both directions.
2
Sample # 1 2 3 4 5 6 7 8 9 10
E
W- Vehicle speed (mi/h) 42 45 55 57 50 43 37 35 60 53
Time headway (s/veh) 2.1 2 2.7 2.5 1.9 2.4 2.3 2.3 2.5 2.3
N-S
Vehicle speed (mi/h) 24 25 30 30 27 22 40 28 35 25
Time headway (s/veh) 2.8 3.1 3.2 2.9 3.6 2.7 3.4 2.5 2.5 3.3
Pedestrian speed (ft/s) 3 5 6 7.5 4 6 5.5 3.5 4 7
