Area Traffic Control Systems

7/31/2019 Area Traffic Control Systems

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CE 310: TRANSPORTATION ENGINEERING

AREA TRAFFIC CONTROL SYSTEMS

JAYANT PATIL (09004023)

AVISHMA MATTA (09004078)

VIKAS SHARMA (09004028)

VINAY KRISHNAN (09004017)

VISHAL KHATRI (09004025)

WORD COUNT: 2967


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CONTENTS

1. INTRODUCTION2. PAST DEVELOPMENTS

3. MAJOR COMPONENTS OF AREA TRAFFIC CONTROL SYSTEMS

3.1. VEHICLE DETECTORS

3.2. INTERSECTION CONTROLLER

3.3. COMMUNICATION NETWORK

3.4. CENTRAL CONTROLLER

3.5. APPLICATION SOFTWARE

4. ADVANTAGES OF AREA TRAFFIC CONTROL SYSTEMS

5. NETWORK CONTROL STRATEGY

6. STATE OF THE ART IN ATCS

6.1. SPLIT CYCLE OFFSET OPTIMIZATION TECHNIQUE

6.2. SYDNEY COORDINATED ACAPTIVE TRAFFIC SYSTEM

6.3. COMPOSITE SIGNAL CONTROL STRATEGY

6.4. OTHER MODELS

7. CASE STUDIES

7.1. CoSiCoSt

7.2. SCOOT

8. FUTURE SCOPE OF ATCS

9. CONCLUSION

10.REFERENCES


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1. INTRODUCTION

In recent years there has been a major rise in the volume of vehicles in major cities across the

world. This has resulted in traffic management problems such as congestion, delays, accidents,

pollution, increased fuel consumption etc. A need has arisen for proper traffic management

measures, policies and systems. Area Traffic Control Systems are intelligent, real time systems

that optimize traffic signal settings in an area, based on data obtained from vehicle detectors to

reduce vehicle delays and stops.

The Area (or Adaptive) Traffic Control Systems have two main functions:

1.Controlling Traffic Signal Timings depending on the data acquired by the vehicle detectors.

2.Providing drivers (public and private vehicles) with traffic information.

2. PAST DEVELOPMENTS

The first electronic traffic signals were introduced by the Cleveland Engineers in 1914. Denver

Engineers used analogue computers with sampling detectors to select the most appropriate

signal timing from programs. The development of traffic control systems started in 1960s. These

first generation systems monitored traffic flow continuously and initiated the appropriate

algorithm from a database to give optimal signal settings.

In 1973, a full Adaptive Traffic Control System called SCOOT (Split Cycle Offset Optimization

Technique) was developed by the Transport Research Laboratory (TRL) in collaboration with

the UK Traffic Systems Industry.

The Australian SCATS (Sydney Coordinated Adaptive Traffic System) was developed in the

1974 in Sydney by the Roads and Traffic Authority.

In the 1980s and 1990s, these traffic control and management systems started to gain wide

acceptance and were implemented for both freeways and urban streets.Developments in microprocessors and vehicle detection mechanisms led to further

advancements in control algorithms and strategies for traffic control systems.

Today, the traffic monitoring and control systems are mature and the emphasis is on

implementation of effective operational tools. Presently, there is a wide array of system

designers, hardware manufacturers and suppliers and software developers to choose from, for

system selection. (FHWA, 2005)

3. MAJOR COMPONENTS OF AREA TRAFFIC CONTROL SYSTEMS

3.1 Depending on the type of sensors, vehicle detectors collect data for vehicle volume, average

speed, class, gap, headway, occupancy, queue length measurement, weight, corridor traveltime etc.

Vehicle detection technologies contain three components: a transducer which detects the

vehicle, a signal processing device converts the transducer output to electrical signal and data

processing device converts this into useful traffic parameters.


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Detectors can be broadly classified into :

Intrusive Sensors - these include inductive loops, magnetometers, microloop probes,pneumatic road tubes, piezoelectric cable, bending plate (weigh-in-motion), piezoelectric (WIM),load cell (WIM), capacitance mat (WIM) sensors. Of these the inductive loop detectors are mostwidely used as they are relatively low cost and the technology is mature.

Non-intrusive sensors these include video image processing, microwave radar, laser radar,passive infrared, ultrasonic, passive acoustic array and combinations like passive infrared andmicrowave Doppler or passive infrared and ultrasonic detectors.They measure vehicle count, presence, vehicle speed, vehicle classification, and have multiple-lane, multiple-detection zone coverage.

3.2. Intersection Controller consists of electronic equipment placed at the signal. The data

acquired by the vehicle detectors at various points on a road network is sent to the Signal

Controller which then relays it to the Central Control (except in CoSiCoSt and similar systems

where it also does split optimization, Muralidharan et al).

3.3. Communication Network: The data is sent from Intersection Controller to the Central

Control which after analysis of the data updates the time plan to all intersection controllers in the

area through this UDP Internet Protocol based network communication link.

3.4. Central Control: The Central Control System comprises of the ATCS Server, Operator

Consoles, external storage devices etc. The master controller takes complex decisions based

on the traffic data. The type of decision includes calculating the cycle time, removing or adding a

junction from the network area, isolating a junction, selecting plan from the database etc.


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3.5. Application software is integrated into the intersection controller to recieve detector inputs,

process status data, compute signal timing and driving signal lamp load switches.

Figure 1. Basic Components of ATCS

The figure depects the components of a typical Area Traffic Control System with the vehicle

detector, Intersection Controller, Central Control, Communication network

4. ADVANTAGES OF AREA TRAFFIC CONTROL SYSTEMS

ATCS provide a management measure to tackle traffic congestion since they increase volume-

capacity ratio of a network. For a road user, this implies greater average speed due to less

delay and stoppage time, besides reducing fuel consumption and atmospheric pollution (FHWA,

2005).

The ATC system is equipped with the fault detection and logging mechanisms which are

triggered when there is a fault in data collection or transmission. This facilitates prompt repair

and maintenance action.

5. NETWORK CONTROL STRATEGY

The algorithms used by ATCS are, in general, a hybrid of mathematical and heuristic models.

Models have been developed to optimize cycle time in an intersection, relative cycle times at

nearby intersections and the offset time of these cycles. They are briefly described below.

Split optimization includes algorithms to calculate optimal cycle time at an intersection and the

time allotted to each approach or stage. During a red signal at an intersection, sensor loops

present at the stop line register a demand for right of way. After the mandatory minimum green


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time is executed, if the sensors continue to register demand, then the green time is extended by

the traffic signal controller until the sensors stop registering demand, subject to the maximum

green time allocated for that approach by the central control. In case the sensors register a gap

in the flow of vehicles, the green time allocated to that stage is immediately terminated and the

next stage is opened. Thus this stage would have the advantage of additional time due to pre-

empting of the previous stage. Normally, this additional time is given to the approach carryingthe maximum traffic at the intersection.

In order to check the effectiveness of the stage timings and cycle lengths allotted to the signal

control by the central control, a feedback mechanism is developed. Stages that use only a

fraction of the green time allotted to them or stages which are so saturated that the green time

allotted to them is insufficient to clear the queue require revised settings and this is done by the

feedback provided to the central control by the signal control system. Accordingly, highly

saturated stages are allotted more green time, keeping the cycle length same, if possible. If not,

care should be taken to avoid oscillations in cycle time and maintain signal coordination since

several intersections with similar characteristics may operate on a common cycle time.

In order to ensure smooth flow of traffic, the relative cycle lengths of nearby intersections should

also optimized. Therefore intersections with similar traffic volume characteristics are grouped

together considering their geographical distribution to operate on a common cycle time.

Whereas intersections with high disparity in traffic volume characteristics are either isolated or

are accommodated in group with half or double cycle time. The purpose is to ensure that traffic

which is smoothly dispersed at one intersection gets similar conditions on reaching the next

intersection. The common cycle time for intersections belonging to a particular group is taken as

the cycle time of the intersection with maximum traffic volume in that group, i.e. the critical cycle

time.

Based in these explanations, it may be inferred that an intersection with similar trafficcharacteristics as the critical intersection, but not as saturated, is less efficient since it is forced

to operate at the common cycle time that is, the critical cycle time. However, this is not true

since the difference between the common cycle time and the required cycle time for such an

intersection is allotted to some stages in the intersection, identified as priority stages. These are

the stages contributing traffic to the route with the maximum volume of traffic in the area and

hence are given the advantage of additional time to ensure that they are dispersed smoothly.

Apart from this, any additional time due pre-empting of any poorly saturated stage is also given

to the aforementioned stages.

The third parameter to be given due consideration is the offsets between stage timings of

intersections. The purpose is to minimize the stopping time of a platoon arriving at anintersection by coordinating signal settings between intersections. The flow profile in an arterial

road is determined by providing sensor loops at strategic locations. Based on this flow profile,

the intersection controller calculates the ground speed of the platoon of vehicles and sends this

information to the central control which in turn calculates the optimal offsets and applies them to

the network to achieve maximum coordination between intersections.


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6. STATE OF THE ART IN ATCS

6.1 SPLIT CYCLE OFFSET OPTIMIZATION TECHNIQUE

Split Cycle Offset Optimization Technique (SCOOT) is an urban traffic control system developed

in 1973 by Transportation Research Laboratory in collaboration with the United Kingdom traffic

systems industry. Over the years, it proved to be an effective and efficient tool to manage traffic

at signalized road networks (Hunt et. al, 1981) and is now used in over 170 towns and cities in

the United Kingdom and across the world. The first ATCS project in India, consisting of 47

junctions at National Capital Region, New Delhi, has been executed using SCOOT by CMS in

collaboration with Peak Traffic Systems, UK.

SCOOT essentially uses a variant of the TRANSYT optimization model that runs in a

background called SCOOT kernel. Traffic volume data, continuously obtained at all approaches

of intersections in a network, are the input to the kernel, which generates optimal signal timings

and communicates it to the intersection controller. The intersection controller uses these

suggested timings, in combination with the changing traffic demand, to make incremental

adjustments to the cycle length, stage timings and offsets for the current and next cycles (Head

et. al, 1992).

Several problems have been reported in the implementation of SCOOT in India. Most

prominently, SCOOT is not designed for the heterogeneous traffic conditions prevalent in India

where drivers tend to use available road width rather than sticking to the lane. Secondly, it has

been reported that the interface of SCOOT is difficult to handle and it traffic terminologies are

different from those used India. Thus, adaptations are required to implement SCOOT in Indian

conditions.(Muralidharan et al.)

6.2 SYDNEY COORDINATED ADAPTED TRAFFIC CONTROL SYSTEM

Originally developed for Australian cities in 1974, SCATS is an adaptive system which optimizes

cycle time, stage time and offsets in response to real time traffic. However, unlike SCOOT which

is based on an optimization model, SCATS uses a library of plans to select from and therefore

relies extensively on available traffic data. In this context, it has been loosely described as a

feedback control system (Head et. al, 1992).

Similar to SCOOT, it has been reported that SCATS lacks an user friendly interface and is

perceived to be excessively complex and labour intensive operationally.

SCOOT SCAT

Centralized System Distributed SystemUpstream Detection Stop line DetectionFixed Traffic Regions Adjustable Region

Fallback - Fixed Fallback - VAModel based - Time generated Algorithmic - Plan Selection

SCOOT vs SCAT a comparison

Source Presentation by Prof.Tom Mathew (IIT-B) and P Ravikumar (CDAC-T)


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The table summarizes the different aspects of SCOOT and SCAT. While SCOOT is designed as

a centralized system for fixed traffic regions, SCAT is a distributed system for adjustable

regions. The vehicle detection is done at an upstream cross section in SCOOT and at the stop

line in SCAT. SCOOT is a model based system in which the solution is time generated while the

SCAT provides an algorithmic plan selection.

6.3 COMPOSITE SIGNAL CONTROL STRATEGY

While developing an area traffic control system for a developing country like India, several

considerations need to be taken into account which are not applicable to developed countries.

For instance, SCOOT and SCAT assume less heterogeneity in traffic vehicles and lane

discipline is followed by everyone except a very small minority. In contrast, the traffic in India is

highly heterogeneous & not separated and lane discipline is rarely followed. It is also assumed

that there is no lane change in the detection zone, which again, is highly unlikely in Indian cities.

This results in wrong vehicle count estimation and detectors failing to report the correct turning

vehicle proportions at intersections. There are other problems like poor road network planning in

the cities, side roads, uncontrolled on-street parking, pedestrians and road side vendors

encroaching the road space, data loss due to power failure, network failure, availability of funds

etc. Thus classical methods of signal time computation cannot be applied in this case because

of the complexities involved in the calculation of Passenger Car Units (PCUs) in real time

(Muralidharan et al).

Composite Signal Control Strategy (CoSiCoSt) is an indigenous area traffic control system

developed by Centre for Development of Advanced Computing (CDAC), Thiruvananthapuram. It

uses appropriate modifications to previous ATCS such as SCOOT to suit Indian conditions.

Most notably in this regard, methods to synchronize heterogeneous road traffic and the ATCSand methods for vehicle identification to obtain traffic count have been developed. Currently, it

has been implemented in Pune, Kolkata, Jaipur, Ahmedabad and Bangalore. However, certain

limitations have been identified and the model needs better offset calculation, an optimization

model for local control, optimization for network level traffic management (Source - Presentation

by Tom V. Mathew).

6.4 OTHER MODELS

Others models of area traffic control systems developed include OPAC (Optimization Policies

for Adaptive Control), RHODES (Real time Hierarchical Optimized Distributed and Effective

System), ACS-Lite, SPOT/UTOPIA (Urban Traffic Optimization by Integrated Automation),

MOTION (Method of Optimization of Traffic Signals in Online controlled Networks), ITACA

(Intelligent Adaptive Control Area), RTACL (Real time Traffic Adaptive Control Logic).

7.CASE STUDIES

7.1 CoSiCoSt

CoSiCoSt was implemented in 38 junctions in Pune by CDAC in 2006. The project was jointly

funded by DIT and Pune Municipal Corporation at the cost of Rs.597.98 lakhs. A study


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conducted by CDAC in 2007 (Muralidharan, Ravikumar et. al.) regarding the various measures

of effectiveness of the implemented systems gave the following results:

1. Average travel speed increase in the range 2-12%

2. Reduction in average delay in the range of 11-30%

3. Estimated annual fuel savings in the year 2006 due to implementation of ATCS is about

Rs.4.77 crores.4. Estimated annual time saving benefits due to implementation of ATCS is Rs.0.83 crores.

5. Total annual savings due to implementation of ATCS on 6 project corridors is about

Rs.5.60cr

6. Overall increase in traffic volume is about 9.06%

7.2 SCOOT

The results of a study titled SCOOT Adaptive Signal Control: An Evaluation of its Effectiveness

over a Range of Congestion Intensities by Chintan S. Jhaveri, Joseph Perrin & Jr. Peter T.

Martin for Transportation Research Board(January 2003) are summarized below. The study

aimed at testing the effectiveness of SCOOT using CORSIM(a simulation software).

The SCOOT-CORSIM Interface (developed by University of Utah) was used to test thesimulation of networks under SCOOT control. Modeling of the test corridor at different

congestion levels proved the benefits of SCOOT over fixed time plans. This was tested on two

real-world corridors (in Salt Lake Valley) simulation.

The results were as follows:

1. Delay reductions for SCOOT over fixed-time control at 0.7 volume/capacity ratio were

8% and 13% at 0.9 volume/capacity ratio. But this reduced to a 0% for an oversaturated

1.1 ratio. Thus it performs better at undersaturated traffic flow conditions and the

performances improves as the corridor approaches saturation but the benefits are

minimal. For oversaturated conditions, it behaves like a fixed time control system. This is

because all directions demand maximum green time and any depend actuated

optimization system would thus behave like a fixed time control.

2. Validation was found to be an important requirement. A nonvalidated system performed

219% worse (and a validated performed 8% better) than the fixed time system.

3. The two real-world corridors simulation proved that SCOOT reduced delay (14%

reduction), travel time and queue lengths as compared to an updated fixed time plan.

8. FURTHER SCOPE OF ATCS

ATCS can be integrated with other features like:

1.Variable Message Signs (VMS) systems are used to direct drivers to the closest car parking

that has space available or to provide other information to the driver like traffic density along aroute in real time.

2.Emergency Green Wave Routes provide a continuous chain of green signals along a

predefined route to provide the emergency response vehicle with highest priority

3.Incidents Detection: Incidents are complex scenarios that can cause traffic congestion. Traffic

congestion is a result of lower traffic flow through the arterial road which itself is a consequence

of decrease in roadway capacity. These incidents can be detected through videographic


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techniques and the corresponding intersection can give more green signal time to this route,

thus clearing the accumulated traffic.

4.Diversions: The ATCS can take input from an external source to implement a predetermined

diversion as in the case of a regular bridge closure or a road closure due to some maintenance

activity.

5.Prioritization: The ATCS can be programmed to favour specific routes considering particulartraffic management policies. This can be done by assigning different weights to the routes at an

intersection.

9. CONCLUSION

Area Traffic Control Systems have been proven to be beneficial over fixed time traffic control

systems (V. Muralidharan et al, Peter Martin et al). There is significant reduction in delays and

stoppings after the implementation of ATCS at various traffic networks throughout the world. In

a developing country like India, transportation plays a crucial role in growth. As the cities are

getting more crowded, the road transportation facilities are moving towards saturation. Thus

there is a need of improving the efficiency of utilization of these facilities in addition toconstructing new ones. ATCS like CoSiCoSt can be designed and used to suit the Indian traffic

conditions. Further research should be carried out in this area.


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REFERENCES

1. Suresh P.S. (2009). Traffic models for real time area traffic control systems in

heterogeneous traffic conditions. PhD Thesis, IIT Bombay.

2. Shabade A.M. (2009). Urban intersection modelling for area traffic control in

heterogeneous traffic. M.Tech. Dissertation, IIT Bombay.

3. Revade R.S. (2008). Evaluation of an area traffic control system and saturation flow

model for heterogeneous traffic. M.Tech. Dissertation, IIT Bombay.

4. Revathy Nair. (2010). Development of system architecture of area traffic control system

for heterogeneous traffic. M.Tech. Dissertation, IIT Bombay.

5. Suraj Shinde. (2007). Evaluation of area traffic control system.M.Tech. Dissertation, IIT

Bombay.

6. Kajal Dubey. (2008). Conceptual architecture and progression model for an area traffic

control system. M.Tech. Dissertation, IIT Bombay.

7. Ravikumar P., Tom V Mathew. (2011). Second Generation CoSiCoSt. IIT Bombay and

CDAC, Thiruvananthapuram.

8. Muralidharan V., Ravikumar P. (2007). Area Traffic Control System implementation atPune- Case study. CDAC.

9. Chintan S. Jhaveri, Joseph Perrin Jr., Peter T. Martin. (2003). Scoot Adaptive Signal

Control: An evaluation of its effectiveness over a range of congestion intensities.

University of Utah.

10. Tavladakis K., Voulgaris N.C. (2006). Development of an Autonomous Adaptive Traffic

Control System. Technical University of Crete.

11. A.G. Sims, K.W.Dobinson, (1979) The Sydney Coordinated Adaptive Traffic system

philosophy and benefits.

12. Technical Specification of Area Traffic control system, Webel Mediatronics,

http://www.webelmediatronics.in/

13. Muralidharan V., Ravikumar P., Binala S. and Tagore M. R. (2006) A Composite Signal

Control Strategy for Indian Roads, Journal of Indian Highways.

14. Federal Highways Association. (2005) Traffic Control System handbook, Publication No.

FHWA-HOP-06-006
http://www.webelmediatronics.in/http://www.webelmediatronics.in/http://www.webelmediatronics.in/

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Area Traffic Control Systems