Dubai: Like most major cities in the world, traffic congestion costs Dubai a lot despite continuous efforts by the authorities to tackle it. In 2013, Dubai’s economy was set back by Dh2.9 billion in terms of loss in working hours, time and fuel.

The most common feature of every modern road network is a traffic light, which according to some facilitates the movement, while some feel it hampers the flow of traffic.

Though the authorities come up with flyovers and bridges every other day, replacing the junctions and roundabouts governed by traffic lights, it is not practically possible to avoid the signals altogether.

In a city like Dubai, which is home to 1.5 million vehicles and a sprawling road network of around 3,760 kilometres of roads, traffic lights play an important role in regulating traffic, particularly in the central business districts.

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Over the years, as Dubai expanded, the traffic system has also become more advanced.

Gulf News takes you behind the scenes of Dubai’s smart traffic system to give you a glimpse of how the system works.

Dubai has more than 800 big and small signalised traffic junctions that are connected to the central traffic command. Most of Dubai’s traffic junctions are run by an advanced signalling sytem called SCOOT.

SCOOT system

SCOOT or Split Cycle Offset Optimisation Technique, is adaptive and responds automatically to traffic fluctuations. It does away with the need for signal plans that are expensive to prepare and keep up to date.

The Roads and Transport authority (RTA), which manages the traffic system, uses three different signalling systems.

“We have fixed time [in which the lights change], which is very rare; then we have vehicle-actuated system, which is dependent on sensors and it has minimum and maximum timings. We also have SCOOT which covers most of Dubai’s traffic junctions, including all big junctions,” said Maitha Mohammad Bin Adai, CEO of RTA’s Traffic and Roads Agency.

“SCOOT calculates the time of each cycle based on the number of vehicles determined through sensors, and has minimum and maximum timings in order to adjust traffic flows accordingly, making movement [of traffic] more reliable,” she said.

Every signal operation has three components: phase, stage and sequence.

“Each movement by itself is a phase, like going straight is one phase and [turning] left is another phase.

Then follows the stage.

“A stage is a group of phases that run together with no conflict such as stage A, B, C etc.” For example, a stream of cars go straight, others go left and some go right, simultaneously at a traffic junction. These are all during one light change but in different directions, so phases A,B,C and D are all happening with no conlfict.

Finally comes the sequence.

A sequence is the way the stages are arranged like ACBD, ADBC or ACDB etc.,” she said.

It is this traffic sequence that confounds motorists at times with many wondering about the basis of this sequence.

“Sequence can be defined as the way signal movements are arranged to avoid conflicts between them. It signifies which stage can go first and then which one should follow and so on. In SCOOT, this depends on the volume of traffic in each phase,” Bin Adai said.

Signal time

One of the most contentious issues of traffic signals is the duration of green and red lights and on what basis they are decided. Motorists usually have a hard time accepting the green or red time they get, wherever they are.

Bin Adai explains: “There is minimum and maximum time defined. Normally, the standard green time duration for vehicles is not less than seven seconds plus inter-green (between red and green) nine seconds. However, the longest green time is different from junction to junction and depends on the traffic volume and the size of the junction.”

The duration of a signal usaully depends on the structure and geometry of a junction. However, in an adaptive system, the volume of traffic dictates the green or red time allowed.

“The duration of a red light depends on the mode of operation. In a normal operation, it cannot exceed 255 seconds. The minimum time of an approach is seven seconds. Normal U-turns and pedestrian phase signals are the shortest red lights,” she said.

She added: “Our system takes a decision based on traffic volume on each approach at the junction. It always tries to optimise traffic discharge to reduce traffic on the junction.”

Predictive systems the way forward

At any particular junction, SCOOT allows the highest green time to a phase with biggest traffic volume. For example, in the evening traffic heading towards Sharjah on Al Khaleej Road at the Hyatt Regency interchange, tailbacks can be all the way up to Bur Dubai via Shindagha Tunnel. To reduce congestion in this phase, SCOOT allows minimal green time in all other directions, while Al Khaleej Road gets maximum green time. This usually causes congestion in other phases.

Bin Adai said RTA is constantly working on improving its system to ensure better flow of traffic across the city.

Traffic signals an important tool against speeding

“Traffic counts and travel run studies are being carried out by RTA continuously at the road network. And depending on the results and cause of congestion highlighted, RTA always looks for ways of improvements,” said Bin Adai.

“Some of the regular steps taken by RTA are: continuous validation and fine-tuning of the signalised junctions; adopting new proven technologies that might help achieving better level of service; and designing a set of quick wins that always enhance the junctions either by additional minor geometric corrections or by trying other modes of operations,” she said.

Types of signals

Signals are classified according to their purpose:

Ped signals (push buttons)

U-turn signals (one movement)

3-leg intersection

The regular 4-leg vehicle intersection

Red light duration

Cannot exceed 255 seconds

Minimum time of approach

Seven seconds