Traffic lights

Colours of safety

Stop says the red light
Go says the green
Change says the amber one
Blinking in between
We all must obey them
Even the queen ...

Many of you must be familiar with this little rhyme on traffic lights, cautioning you on the rules to follow whenever you come across them on the roads.Traffic lights, sporting the colours red, yellow (or amber) and green could be seen at many junctions (or intersections as the engineers call them).

They stand like 'lone sentinels' (sentries) at these places, directing traffic by flashing the three colours at pre-determined intervals.

With the increasing number of vehicles and people on the roads today, it is not hard to imagine what chaos (disorder) there would be, if there were no means of control. When it comes to methods of controlling traffic, there are six different ways to do this; self control, sign control, police control, traffic lights, overpasses (flyovers) and roundabouts! All these methods are used to control the traffic from different directions, including pedestrians.

We know that traffic lights play a key role in ensuring road safety. So, let's check out some interesting facts about them.

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Why traffic lights were introduced

By now you must be aware that Traffic Light Signals (TLS) systems are useful to ease traffic congestion at various places and also control movement at hazardous points such as railway crossings.

Basically, TLS systems were introduced with the aim of (a) ensuring that the 'shared area', the road area used by different traffic movements, especially at intersections, is used in an ordered disciplinary manner, (b) to avoid potential hazards on conflict points (places where different traffic movements meet) (c) to assure an opportunity to use the 'shared area' on a set phase (arranged stage) and timings.

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When and where they were first installed in Sri Lanka

They were first installed on September 17, 1986 at the Flower Road, Green Path junction, Kynsey Road, Horton Place junction and Castle Street, Senanayake Road junction.

It had cost around 40,000 Sterling pounds at that time as they were imported from England, but now these traffic lights are made in Sri Lanka by the Road Development Authority (RDA) in collaboration with the University of Moratuwa.

All the TLS systems installed in Sri Lanka at present have been made in Sri Lanka. It had saved millions of rupees for the country.

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How it is decided that TLS are needed at particular junctions

If traffic congestion is reported or observed in a place, the authorities initiate (start) a survey to make sure that the place really needs some sort of traffic control. They can be traffic lights, traffic signs or a roundabout. So, to determine that, representatives from the RDA or CMC are stationed at particular points, for around 16 hours a day.

They take a count of all the traffic that passes through the junction or crossroad and note down to which side more vehicles turn to, at this place. The RDA has a special device called a 'logger' to make this process easy. It is a pre-programmed device.

All the representatives stationed at the junction to count the different turnings have these devices. They just have to press a button when each type of vehicle moves on. Then the data taken from all the loggers will be stored into one database in the computer.

Using this data, engineers can decide which roadway has a heavy traffic flow and programme or set the traffic lights to give way for a longer period to traffic turning to that particular side.

For instance, the green light stays on for a longer period on the High Level Road which has a heavy flow of traffic. These traffic control cycles can be set to change every 15 minutes, but, now they are set to change every two to three hours.

These can be different according to the place. Average timings for changing of lights at each junction are decided by the data collected through a manual count.

These TLS systems are adjusted to work on traffic flow of a normal day, but if there is a special incident happening, for example a bomb explosion, closing of a road or an accident, the TLS systems may fail to function to suit the flow of traffic at that particular time.

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What countdown traffic light systems are

You must be aware that there are special lights for pedestrians to cross at junctions. Some of these lights also have a system that indicates how long it will take for the colours to change by giving a countdown.

There are two such TLS at the Borella, Devi Balika junction and at Union Place. The Union Place countdown specifies the number of seconds left for the pedestrians to cross the road, but the one at Borella focuses on vehicles.

The pre-determined phasing and timing is calculated on the basis of traffic counts done at junctions at the design phase. Minor adjustments are done while at operation, to accommodate changes that occur while the system is put in to operation.

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How the lights change colour

Have you wondered how the three colours keep changing with no one present to operate them manually? Well, they function according to pre-set timings stored in a memory, which is processed through a processor, powered by electricity. In some countries, the TLS are powered by solar power.

The TLS in our country are still operated by electric halogen bulbs. Now attempts are being made to convert these bulbs into Light Emitting Diode (LED) which saves power.

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Who is responsible for the TLS systems and how many are there throughout the country?

The RDA at Sethsiripaya, Battaramulla is responsible for the traffic lights installed at all the national roads, and the municipal councils of every city are responsible for the traffic lights in their area. They are responsible for the installation and maintenance of TLS systems.

A total of 116 TLS are there in Sri Lanka, excluding the ones installed and operated by the Railway Department at railway crossings. Out of these, 58 traffic light signals come under the RDA and another 56 are maintained by the Colombo Municipal Council (CMC). The remaining two are maintained by the Kandy Municipal Council (KMC).

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Are cameras used by TLS systems?

Certain TLS systems are installed with cameras. For instance, the TLS at the Lipton Circus and Horton Place junctions have cameras.

These cameras are not used to control traffic directly, but more as sensors at the moment. They will be used to get data for future amendments to the existing system.

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The methods by which the TLS operate

The TLS systems are programmed on the basis of the time allocation provided to each directional traffic flow, on a cyclic process. It is a fixed time technique. That is, for a particular time interval such as 15 seconds, the cyclic pattern of time allocation will remain the same. This is one method used.

The other method is the vehicle activated time technique. Here the pre-programmed patterns could be adjusted based on the approaching traffic flow which is detected by sensors. Then, these observations made by the sensors are processed by traffic controllers and suitable time allocations are made. However, the second method of operation is not yet introduced in Sri Lanka.

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Future plans

According to the Director Traffic Designs and Road Safety of the Colombo Municipal Council, Nihal Wickramaratne, plans are being made to interconnect all the traffic lights through telecommunication wires.

This will facilitate the free flow of traffic under these new proposals. For instance, a driver passing through a green light at a particular junction will not have to face a red light at the next junction. He or she will be able to drive through freely because all the lights at different junctions will be programmed in the same colours. This is called the 'Green Wave system'.

"With the help of Japan International Cooperation Agency (JICA), we are going to implement a system called Area Traffic Control (ATC) to ease the traffic flow in the country", said Director Planning, RDA, R.M. Amarasekara.

ATC is a system that controls the traffic flow through traffic signals, message signboards, and lane control signals. To implement this new system, a centre with a wide screen will be built and operators will change the TLS cycles using the pictures that appear on the screen which will be sent by cameras fixed to the traffic lights.

At present, when the traffic flow is less(after 9 pm), the amber lights keep blinking to allow the free flow of traffic, but you should always stop at the STOP line at the junctions, to see whether the junction is clear to move.

Proposals are under way to install TLS systems at Vilasitha Nivasa and Duplication Road according to CMC officials. The RDA officials say they intend to install TLS systems at the Nugegoda Supermarket Junction, Nawala Junction, Jubili Post Junction, Mirihana Junction and Pitakotte in Colombo suburbs, Pamankada, Kohuwala, and Pepiliyana on B 084 Road, Ethul Kotte Junction, Parliament Road Junction, and Koswatta Road Junction on A000AB1 Road, five junctions at Kadawatha and one in Mudungoda on A 01 Road, Mahabage, Wattala and Ja-Ela on A 03 Road, Maliban Junction, Golumadama Junction and Panadura on A 02 Road, Wijerama Junction, Moraketiya and Godagama on A 04 Road, Wellampitiya and Kaduwela on AB10 Road.

The letters and numbers used to identify the roads are given by categorising the road according to the status of the road. We will bring you more details about this in one of our future issues.

by Janani Amarasekara