Application and Suitability of Signal Coordination

UNEB GAZDER

Civil Engineering

University of Bahrain

Sakhir, 32038

BAHRAIN

Abstract: - The aim of this study was to apply signal coordination for eight signalized intersections in three

different locations and compare the performance before and after the adjustments. To achieve the above

objective, we collected traffic data from the sites and from the ministry of works. VISSIM software was used

for evaluation and analysis of intersections. SYNCHRO software was used for finding the best timing plan

alongside manual solution (trial-and-error). We got a high delay and bad level of service for all of the selected

intersections before applying the signal coordination. Then the improvement strategy of optimizing signal

timing and coordination was applied to the traffic flow in the study areas. Finally, this improvement was found

to have good effect on the level of service and delays, where we reduced the delay in all the locations by

approximately 34% and improved the level of surface from F to E on Estiqlal highway and 16th December

Highway and from D to C on Tubli highway. The strategies and design from this research can be implemented

on the selected locations and serves as a benchmark for other similar studies in the region.

Key-Words: - Bahrain; Intersections; Signals; Level of service; Timing; Level of Service

Received: April 11, 2023. Revised: October 21, 2024. Accepted: November 15, 2024. Published: December 12, 2024.

1 Introduction

In situations where traffic signals are close to each

other, so that vehicles arrive at the downstream

intersection in platoons, it is necessary to coordinate

their green times so that vehicles may move

efficiently through the set of traffic signals without

the need to have drivers stopping at all the signals.

Bahrain is facing rapid increase in vehicle

registration. Consequently, traffic congestion and

delay has been also increasing, more so, at the

closely spaced intersections. Design of coordinated

signals is one of the approaches to mitigate the

effects of congestion. To this effect, our study aimed

to design coordinated signals at important highways

in Bahrain.

2 Literature Review

Signal Coordination is basically timing a set of

traffic signals along a major roadway to provide

smooth flow and minimal stops [1]. We need signal

coordination to make mobility as efficient as

possible between intersections, and this technique

will make us dispense roadway widening [2]. It will

minimize the percentage of accidents; on the other

hand, it will increase in travel speed which may

have a negative impact in the community [3].

Offset is the difference between two green initiation

times. The ideal time of offset is the time needed by

the vehicles to move from one intersection to

another (distance/Speed); unless, when there is a

queue in the downstream intersection which will

make the coming platoon reduce speed and maybe

stop which we are trying to avoid. So, we have to

adjust the offset by adding some factors, as shown

in equation 1 [4].

  

 󰇛  󰇜 (1)

= adjusted ideal offset, s

L= distance between signals, km

S= Speed, kph

Q= Number of vehicles

h= Discharge headway of queued vehicles, s/veh.

= Start-up lost time at first downstream

intersection, s

Over Saturated Flow happens when demand exceeds

capacity. Because of that, unstable queue will keep

on increasing until it reaches the spillback point.

Therefore, it will block the upstream intersection

(Reducing capacity). In our project all of our

locations are suffering from oversaturated flow

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.10

Uneb Gazder

E-ISSN: 2945-0489

Volume 3, 2024

which makes signal coordination needs more

effective solutions.

The management of traffic in oversaturated

conditions will be slightly different and the priority

will be avoiding queue spillbacks, avoiding

saturation and managing queue formation. There are

many reasons for the intersections to be over-

saturated (demand exceeds the capacity). Some of

them are as follows: Convergence of routes (when

there are lots of routes connecting in small area),

Two major roads crossing each other (each have

high traffic and will lead to definite delay to one of

them or both) or Seasons and events (like sports day

or national day or rainy days) [5].

For over saturated intersections there are two main

approaches to solve the over-saturation: throughput

strategies (which are considered curative) and queue

management strategies (which are considered

palliative). Throughputs strategies are used to

remove the long queue and solve the problem

permanently (Find and use the right cycle, Service

heavy movements more than once in a cycle and

seek all possible available green time). Sometimes

the throughput strategies may not work the way

traffic engineer wants, so we can use queue

management strategies to help stop the queue

increasing in an unstable way (Balance the queues

for conflicting approaches, prevent queues from

spreading congestion) [6].

Signal coordination strategies have been reported to

help with various aspects of traffic, apart from

improving traffic flow. In this regard De Coensel et

al. [7] have reported their positive impact on noise

and air pollution mitigation. Moreover, Zhang et al.

[8] have reported the positive impacts on signal

coordination reducing crash risks. In the same

context, studies have also reported an increase in

proportion of severe crashes due to signal

coordination [9].

There is a lacking in the literature related to

studying effects of signal coordination in Gulf

region, especially for Bahrain. Moreover, the

evaluation of the contextual scenarios in which

signal coordination could perform better is also

missing. These gaps are being filled by the current

study.

3 Study Locations and Signal

Coordination Approaches

3.1 Study Locations

We have three study areas; each area located in a

different position as explained below.

Esteqlal Highway starts from Bahrain Polytechnique

to Baghdad - Esteqlal junction, (26°10'7.13"N,

50°32'37.94"E), and shown in Fig. 1

Fig. 1. Esteqlal Highway Intersections Location

It consists of two junctions affecting each other, and

in peak hours these junctions get over-saturated

especially when the students are leaving or entering

the educational area. The queue starts from

intersection 2 and goes to intersection 1 and keep

increasing and blocking the intersections resulting in

high delay.

16 December starts from Indian school to Sh.

Salman Hwy & Sh. Zayed Hwy junction, (26°

9'25.80"N, 50°32'19.65"E), and shown in Fig. 2.

Fig. 2. 16th December Highway Intersections Location

These two junctions affect each other and in peak

hours these junctions (intersections) get

oversaturated creating unstable queue that increase

with time and block the upstream intersection

(intersection 1)

Tubli highway starts from Bahrain Map Monument

to Wastewater Treatment Station,

(26°12'12.47"N,50°34'1.07"E),(26°11'52.55"N,50°3

3'28.80"E), and shown in Fig. 3.

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.10

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Fig. 3. Tubli Intersections

In this location, there are four junctions

consequently, starting from Bahrain Map Monument

junction and ending up with waste-water treatment

plant junction. Moreover, the distance between first

junction 1 and junction 2 is approximately 280 m,

while the distance between junction 3 and junction 4

is roughly 425 m. In this study location the queue is

forming alongside the main street in both directions.

3.2 Signal Coordination Approaches

This study deals with locations which have over

saturated flow conditions. Over saturated flow

happens when demand exceeds capacity. Because of

that, unstable queue will keep on increasing until it

reaches the spillback point. Therefore, it will block

the upstream intersection (Reducing capacity). The

management of traffic in oversaturated conditions

will be slightly different and the priorities are set to

avoid queue spillback and saturation, managing

queue formation and providing equitable service [5].

3.3 Approaches to Address Over-Saturation:

For over saturated intersections there are two main

approaches to solve the over-saturation, Throughput

strategies (which it considered curative), Queue

management strategies (which it considered

palliative) [10]. Sometimes the throughput strategies

may not work the way traffic engineer wants, so we

will use queue management strategies to help stop

the queue increasing in an unstable way [11].

It is difficult to exaggerate how often the basic

problem is poor signalization. Once the

signalization is improved through shorter cycle

lengths, proper offsets and proper splits, the

problem may disappear. Or maybe the problem is

too much traffic where we will use the concept of

phase re-service to manage the spread of congestion.

These two options may be used as distinct treatment

or as part of a metering plan (as mentioned earlier).

For intersections located along arterial streets,

isolated operation can often be improved by

considering coordination of the major street

movements along the arterial. Common cycle

lengths are often employed to facilitate this

coordination. It is not necessary that when cycle

length increases, the intersection capacity will

increase. But it is important to discharge the queue

in which case shorter cycle length will be better

which could be estimated from Equation 2.

≤

(L/D)(3600/vi) (2)

C = Cycle length, sec.

L = Length of downstream link in a congested

environment, ft.

D = storage space per vehicle, ft.

vi = The discharge volume per downstream lane

(critical flow – veh/hr/lane).

Note that ‘D’ equals approximately 25 feet, and ‘L’

taken as 85% of its origin value to keep queue away

of discharging intersection (assuming that the

downstream link can itself discharge the arriving

queue in one cycle) [10].

The spacing of signalized intersections ‘L’ affects

how one times the signals. For signals that are

sufficiently far apart that they can be considered

independent of one another, intersections may be

operated freely without need for or benefit from

coordination, depending on the degree of congestion

on the facility. For most arterial streets with signal

spacing between 500 feet and 0.5 mile (2,640 feet),

coordinated operation can often yield benefits by

improving progression between signals. On arterials

with higher speeds, it can be beneficial to coordinate

signals spaced a mile (5,280 feet) apart or even

longer. Signals that are located very close together

(less than 500 feet) often require settings that

manage queues, rather than progression, as the

dominant policy. It may also be beneficial to operate

two intersections with very close spacing with a

single controller.

4. Data

Some of the geometric data has been collected from

the field, for e.g., the number of lanes and their

approaches. The traffic volume data was collected

from the roads department in the Ministry of Works

(for each intersection at all hours). The peak hours

for traffic data collection are determined from the

acquired data. Speed measurement was carried out

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.10

Uneb Gazder

E-ISSN: 2945-0489

Volume 3, 2024

in the field by measuring the time taken by vehicles

to pass trap length. We took the speed of 62

passenger cars with a minimum trap length of 50m.

The average spot speed can be computed from

Equation 3 [12].

  

 (3)

Where:

S = the average measured spot speed of vehicle,

kph

d = the segment length, m

 = the time required for vehicle () to

transverse the section, sec

Saturation Flow Rate is the flow achieved if each

vehicle consumes ‘h’ seconds of green time and if

the signal were always green, then ‘s’ vehicles per

hour could enter the intersection [13]. Due to

(COVID - 19) it was not possible to study with high

volume. So, we took an approximate number taken

from a case study in Qatar [14]. Therefore, the

Saturation Headway will be 1.55 seconds. For the

signalized intersections, Phase Lengths are collected

from Ministry of Works. The value of lost time is

taken as the default value (2.5 sec).

5. Calculations

The optimization of the intersections on 16th

December Street is done by SYNCHRO program.

For the other study locations, we had to optimize

manually by following the next steps:

1. Development of a safe and effective phase

plan and sequence. By using the same phase

plan and sequence for the selected

intersections and adding every two closed

intersections phase plan with a little

modification to eliminate any wasted green

time.

2. Determination of vehicular signal needs:

 Timing of ''yellow" (change) and "all-red"

(clearance) intervals for each signal phase.

We assumed the yellow and the all-red

intervals combined as 4 seconds.

 Determination of the sum of critical-lane

volumes (Vc). By adding the volume in

each phase plan and find the maximum one

to calculate the phase time using it.

 Determination of an appropriate cycle

length (C): we assumed at first two minutes

(120 seconds) to check the results and

change it later using trial and error.

 Allocation of effective green time to the

various phases defined in the phase plan-

often referred to as "splitting"' the green

Depending on volumes ration in the critical

lane-volume.

 Calculating the offset time using equation 2-

3 and applying the time on-trial basis in

program till we got the best offset.

 Then, we repeat the above procedure for

different cycle lengths to find the optimal

one.

Now we do not have an equation to find the exact

cycle length. So, we will choose different cycle

lengths and compare them to get the optimal cycle

length. We tried 80,100,120 and 140seconds in

VISSIM program and plot the results of the queue

length and the capacity for each cycle length in

figures 4 and 5.

6. Results and Discussion

Results obtained from the simulation software,

VISSIM and SYNCHRO are shown in Tables I-III

for different study locations. Optimum cycle length

was found to be 100 seconds, in terms of queue

length and capacity. It was found through applying

different cycles lengths and observing the changes

in capacity and queue length. It was plotted with a

best fit curve and optimum value was found where

maximum capacity and minimum queue length were

found. Fig. 4 and 5 present a sample of these curves,

which were prepared for Esteqlal highway. Similar

curves were obtained for other locations which are

not presented here to avoid repetition.

Table I and II show the comparison done with

VISSIM software from Esteqlal and Tubli highway,

while Table III shows the comparison by

SYNCHRO for 16th December highway. The latter

was done due to the complex geometry of the

intersections at the location which could not be

plotted accurately in VISSIM.

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.10

Uneb Gazder

E-ISSN: 2945-0489

Volume 3, 2024

Fig. 4. Determining optimum cycle length using queue length at

Esteqlal Highway

Fig. 5. Determining optimum cycle length using capacity at Esteqlal

Highway

TABLE I: COMPARISON BEFORE AND AFTER SIGNAL COORDINATION AT

ESTEQLAL HIGHWAY

Comparison aspects

Before signal coordination

After signal

coordination

queue length (m)

1000.38

805.68

Capacity (veh/hr)

3878

5327

Level of Service

Delay (s)

228.24

144.55

TABLE II: COMPARISON BEFORE AND AFTER SIGNAL COORDINATION AT

TUBLI HIGHWAY

Comparison aspects

Before signal coordination

After signal

coordination

queue length (m)

1656.28

1479.15

Capacity (veh/hr)

13461

14787

Level of Service

Delay (s)

189.53

133.43

TABLE III: COMPARISON BEFORE AND AFTER SIGNAL COORDINATION AT

16TH DECEMBER HIGHWAY

Comparison aspects

Before signal

coordination

After signal

coordinatio

Signal Delay/vehicle

(s)

170

162

Stops/vehicle

1.27

1.1

Travel time (hr)

699

679

CO emission (Kg)

50.07

48.44

100

110

120

130

140

150

160

60 80 100 120 140 160

Queue Length (m)

Green Time (sec)

2350

2400

2450

2500

2550

2600

2650

2700

60 80 100 120 140 160

Capacity (veh/hr)

Green Time (sec)

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Significant reductions in delay and queue lengths

were observed at all study locations after signal

coordination. Especially, at Esteqlal highway,

wherein the delay reduced by more than 100

seconds and queue length was reduced by 200m.

Similar reduction in queue length was observed at

Tubli highway. However, reduction in delay per

vehicle was 8 seconds on 16th December highway

which would aggregate to a high value for the peak

hours. Total travel time for the highway reduced by

20 hours which is an indicative of this fact.

Moreover, the capacity for all intersections was

increased by more than 1000 veh/hr.

7. Conclusion And Recommendations

The aim of this research was to design coordinated

signals at important highways in Bahrain, to create a

smooth flow and improving the level of service by

minimizing the number of stops and delays.

Furthermore, the effects of signal coordination were

determined and compared for different scenarios in

terms of traffic flow, fuel consumption and CO

emissions. On Esteqlal highway, although the level

of service did not change, we were able to increase

the capacity of the junctions by 1449 veh/hr and

reduce the delay by 37%. In Tubli highway the

capacity of the junctions increased by 1326 veh/hr,

the level of service improved from D to C and the

stop delay have decreased by 35%. For 16th

December street the queue was reduced by 30% and

the average delay per vehicle reduced by 42.5

seconds. All the selected junctions have shown a

significant improvement using signal coordination.

This research is very useful for implementation on

the selected intersections where it has a lot of

advantages in addition to those mentioned above.

For example, it reduces the emissions of CO and

fuel consumption which will improve the air quality.

Our recommendation is to use signal coordination

on the selected junctions in the peak hours while

keeping the current phase plan for off-peak hours.

Other similar locations in Bahrain with closely

spaced intersections should be evaluated for

possible application of signal coordination.

The present study is the first of its kind for Bahrain

and many other GCC countries. Moreover, it

provides evidence of the results of application signal

coordination in different scenarios. Future work

should focus on developing a time period frame to

when the coordination starts and end and use both

soft wares in each study location to get the most

efficient coordination plan and applying the plan on

the real intersections to get the actual data and

results.

Acknowledgment

Special thanks to the Ministry of Works for helping

us during this project, and all traffic engineers

whose we communicated with on social media for

consulting cases.

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The sole author contributed in the present research,

at all stages from the formulation of the problem to

the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The author has no conflicts of interest to declare that

are relevant to the content of this article.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

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International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.10

Uneb Gazder

E-ISSN: 2945-0489

Volume 3, 2024