Question

SKAB / SKAA 3842 - 3- Q2. (a) Table Q2 below gives the flow and saturation flow for all approaches (in pcu/hr) at unsignalised junction in Kluang district. The influence of heavy vehicles, turning movements and all other factors have already been considered. All approaches consist of one exclusive right turn lane (RT), one straight-through traffic (ST) and one straight- through shared with left turn (STLT). Table Q2: Traffic volume at unsignalised junction in Kluang district Approach NORTH SOUTH WEST EAST Movement STLT STRT STLT STRT STLT STRT STLT STRT Flow 215 180 200 175 190 181 200 300 250 225 | 1700 1800 1700 1700 1800 1700 1700 1800 1700 1700 1800 1700 Saturation flow Design a signalised junction according to ATJ 13/87 method (show the signal timing and phase diagram). Use amber, a = 3 sec and lost time due to late start per phase, 1 - 2 sec in the design. For West and East movement, use all-red period, R-3 sec and for North and South movement, all-red period, R = 2 sec. Clearly state your assumptions where applicable. (25 marks) (b) Show/draw any other possible combination of movement/phase. Which combination would you prefer to select and why? (10 marks)

Answer 1

It will be a four phase signal as shown below

North approach means SB, West aproach means EB, so i have kept it in the same order as in the question

First phase is North approach i.e SB

Phase 1 SBL/T SBT Phase 2 SBR NBL/T NBT NBR Phase 3 EBLT EBT/R EBR WBL/T WBT WBR Phase 4

so lets calculate the flow ratio and critical flow ratios for different lane groups.

Critical Flow Saturation Flows/lane Total # of lanes Saturation Flow Given Peak Hour Flow Ratio Flow Ratio 215 0.126 0.112 Phase 1 SBL/T SBT SBR Phase 2 NBL/T NBT NBR Phase 3 EBL/T EBT/R EBR Phase 4 WBL/T WBT WBR 1700 1800 1700 1700 1800 1700 1700 1800 1700 1700 1800 1700 1700 1700 1700 1700 1700 1700 1700 1700 1700 1700 1700 1700 180 200 175 190 181 200 300 250 0.126 0.106 0.118 0.103 0.112 0.106 0.118 0.176 0.147 0.132 0.166 0.138 0.176 225 0.166 283 234 0.581

So sum of critical flow ratios = 0.581

max critical ratio is 0.176 which is less than 0.85

According to ATJ 13/87 method

Intergreen time = Red + amber

= we can calculate it out

Lost time per phase = Driver Reaction Time + Amber Time

So we can calculate, intergreen and lost time for each phase as follows

ATJ 13/87 method Amber Time Start up Lost time Red Time Intergreen "lost time (total/phase) 3.0 2.0 5.0 2.0 5.0 3.0 2.0 5.0 2.0 5.0 Phase 1 SBL/T SBT SBR Phase 2 NBL/T NBT NBR Phase 3 EBL/T EBT/R EBR Phase 4 WBL/T WBT WBR 3.0 3.0 6.0 2.0 5.0 3.0 13.0 16.0 5.0 12.0 10.0 22.0 8.0 20.0

Optimum Cycle Time

C = (1.5L + 5)/(1-Y)

where L = total lost time per cycle

Y = sum of critical flow ratios

so C = ((1.5 *20) + 5)/(1-.581) = 35/.419 = 83.53 secs so round it up to 85 seconds

So Cycle Length = 85 seconds

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Effective Green time for entire cycle = Cycle length - total lost time = 85 - 20 = 65 seconds

so now we can calculate effective green for each phase

Effective green for phase1 = critical flow ratio for phase1/sum of all critical flow ratios * total effective green for entire cycle = .126/.581 * 65 = 14.1 seconds.

So we have for all phases as follows

ATJ 13/87 method Eff. Saturation Flows/lane Flow Ratio Critical Flow Ratio Amber Time Start up Lost time Red Time Intergreen Green name ce lost time lost time (total/phase) time Phase 1 0.126 3.0 5.0 2.0 14.1 Phase 2 0.112 5.0 2.0 5.0 12.5 SBL/T SBT SBR NBL/T NBT NBR EBL/T EBT/R EBR WBL/T WBT WBR 1700 1800 1700 1700 1800 1700 1700 1800 1700 1700 1800 1700 0.126 0.106 0.118 0.103 0.112 0.106 0.118 0.176 0.147 0.132 0.166 0.138 Phase 3 0.176 6.0 2.0 19.7 Phase 4 0.166 3.0 6.0 18.6 3.0 12.0 0.581 | 10.0 22. 0 8 .0 | 65.0 Effective Green Time

So we have the following phasing and timing plan

Phase 1 Phase 2 Phase 3 Phase 4 3.1 3 2 15 3 2 187 33 176 3 3| includes stave ub lost time

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Other possible phase combinations involve protected lefti-turns. For example you can have

Phase 1 Phase 2 EBL WBL EBT/R WBT/R NBL SBL NBT/R SBT/R Phase 3 Phase 4

However in this problem the through flows and left-turns are almost of the same magnitude, so perhaps allowing protected left-turns maynot have that much of an impact. Also for this you need to separate the left-turn flow from the through-flow, which is not possible from the given data, unless you get it directly from the survey counts.

So I would recommend to keep it at split phasing on all four approaches.