Question

1. the following information is provided for an intersection that will have signalization. calculate the signal timing for a two phase system also show the phase diagram .

peak hour volumes: SB/NB/WB/EB;360/300/444/482 vph

PHP; SB/NB/WB/EB:0.92/0.88/0.90/0.82

saturation flow: SB/NB/WB/EB:1500/1500/1800/1800vph

distribution of vehicles for turning movements

	South bond	North bond	West bond	East bond
TM	T R L	T R L	T R L	T R L
% of TM	90 4 6	88 7 5	84 8 6	86 15 1
% of CV	3 0 3	4 14 4	2 8 10	4 15 7

yellow interval 3.1 sec. for SB-NB, and 3.4 sec. for WB-EB; lost time 3.3 sec for each of the phases.

2. its a question from transportation

Answer 1

We are told to assume its a two phase Signal, so we have

	Approach
Phase 1	SB
NB
Phase 2	WB
EB

The phase diagram is shown as

DHV = givent turn flow/phf so for NB it wil be 300/.88 = 341

Now in SB approach 391 is DHB and are given 90% is through volume and 4% is Left and 6% is right

so we have 351.9 through and 39.1 turning vehicles.

But Total qi is given to be 416 so 351.9 + 39.1* (through equivalent factor) = 416

So through equivelent factor = (416-351.9)/39.1 = 1.639

So apply this through equivalent factor for all other movements to get the q

so q for NB = 300 + (41*1.639) = 367

So we can calculate the turn flow ratio and critical ratios. We have as follows

Sum of critical flow ratios = 0.637

We are given lost time per phase = 3.3 seconds

So we have

Optimum cycle time = (1.5*L + 5)/(1-sum(V/S))

Where:
Co = Optimum cycle length (sec)
L = Sum of the lost time for all phases = 3.3 * 2 = 6.6
V/s = Ratio of the design flow rate to the saturation flow rate for the critical approach or lane in each phase

C = (1.5 * 6.6) + 5/(1-.637) = 41.0468 seconds you can round it up to 45 seconds

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Total effective green = cycle time - totallost time =45 - 6.6 = 38.4 seconds

Effective greenphase = (Critical Flow Ratio for that phase/sum of all critical flow ratios) * Total Effective Green

Actual green = Effective Green - Yellow time + Lost time