Who, or What, Decides the Rhythm of Dublin's Traffic Lights?

In a room on the seventh floor of Civic Offices on Wood Quay, Karen Hosie and her traffic-management team glance up at the eight large monitors displaying the major traffic junctions and arteries around the city.

One central screen shows a bus round College Green. On another, an aerial view sweeps the length of the quays up to O’Connell Bridge and beyond, where there is a stream of Friday-morning traffic.

It’s from here that the city’s traffic is monitored, a task not without its challenges, says Senior Executive Officer Hosie.

For the team at Dublin City Council, the focus is getting the balance right between Dublin’s competing transport modes.

These days, it is largely up to technology to calculate how to how to accommodate the pedestrians, cyclists, buses, and cars that vie for first place on Dublin’s streets.

Gone are the days of manual logging.

The city’s major junctions are hooked up to a smart setup called the Sydney Coordinated Adaptive Traffic System (SCATS), says Hosie. Of around 1,000 traffic signals in the city, 850 are connected up.

“The other ones that would not yet be connected to SCATS are smaller, pedestrian crossings that aren’t near a major junction, that can run independently,” she says.

The system was developed in Sydney, Australia in the 1970s and is now in use in cities throughout the world. It takes into account gaps in traffic, and decides on “plans based on those gaps”, says Hosie.

“We first introduced the SCATS system in Dublin in 1989 on 35 initial junctions,” she says. “Then over the years we rolled it out.”

You may have noticed figure-eight shapes cut into the road at junctions in Dublin. These are “traffic loops” that detect how many vehicles are passing through.

By counting the spaces between vehicles, the system learns how heavy traffic flow is and switches between the traffic signals accordingly.

If you can’t move through a junction – because there’s a blockage ahead – then SCATS registers this too; it alters the traffic lights and tries to clear the traffic at another signal.

“What you’re trying to prevent is someone getting a green and going nowhere,” says Hosie.

Back When

Dublin’s traffic management used to be based on “fixed-time frequency”, says Hosie, whereby traffic flows were decided by a council traffic controller who kept watch over the streets and recorded detailed time logs.

There was a bridge period before SCATS, when the council used a similar but less effective technology than the one it uses now, says Hosie. “SCATS would be more scalable. You can expand it to more areas,” she says.

SCATS also allows the council to collect data every two minutes. Based on that, the system tells Hosie and her team at the council what it wants to do next.

Let’s say its measurements show more traffic going in one direction than another, says Hosie. The system then says it wants to adjust the signals accordingly, by slowing or speeding up times.

If a side road is busy, the signal will switch to give it more time; if there’s nothing on the side road, it will switch to flows on the main road or a pedestrian crossing. “The idea is that there’s no waste of time,” she says.

Hitting that pedestrian-crossing button a dozen times in frustration will do nothing, she says. Once is enough.

Future Challenges

One of the most complex spots for traffic sequences in the city is O’Connell Bridge.

One a recent Friday afternoon, the vehicles heading north from Westmoreland Street towards O’Connell Bridge have 25 seconds to cross the bridge before the light turns amber. Three seconds later it’s red.

When the green man appears, pedestrians have 34 seconds to cross in every direction, before he glows amber, and freezes back on red again.

There’s a gap before vehicles are given the green down the quays, and for 35 seconds the light is green, followed by three seconds of amber and then red. The pedestrians ripple out again.

Hosie says that the main day-to-day challenge for her traffic-control team is managing the sheer numbers who pass through the city.

Because the pedestrian takes priority in Dublin’s traffic system – followed by cyclists and then vehicles – striking a balance is not always easy. College Green is particularly tricky.

“But then there’s an awful lot of people who go through on buses too,” says Hosie. “You’re trying to get a fine balance between getting people to where they want to go as well as anyone who’s come off a bus, or the DART, or in the future the Luas, so they can all get to their destination quickly and safely.”

“The last thing you want to do is to have people waiting too long to cross the road because people will just cross the road without the traffic signalling,” she says.

Junctions are varied in complexity, but O’Connell Bridge, for the next few years, will prove a challenge for Hosie and her team.

The new Luas trams are too long to stop on O’Connell Bridge. “The complexity there is to try to make sure the Luas reaches one side of the bridge and clears to the other safely,” says Hosie.

But Hosie and her team will also have to make sure that each bus route can flow up O’Connell Street, that pedestrians can cross safely at one of the city’s busiest crossings, and that traffic signals are adjusted accordingly.

“You’re trying to strike that balance,” she says.

The Troubleshooters

It’s not entirely up to technology to decide who gets to go; people play their part too – not least the traffic management staff who work 24/7, 365 days a year.

There are four ways that the council’s traffic-control department learn about the traffic challenges that people face in the city: from local councillors, from individual Dubliners, from organisations, and, of course, through the SCATS system.

The council’s area engineers assess any traffic queries, go and do surveys, and consult locals.

“We would get a number of queries in relation to junctions all over the city,” says Hosie. “Some queries are along the lines of ‘the pedestrian light’s not long enough’, and we would look at ways to improve that for people.”

Green Party Councillor Ciarán Cuffe, who chairs the council’s transport committee, says there needs to be a faster response to traffic queries.

“We got to a stage about six months ago where there was a backlog of hundreds of traffic queries in each area in Dublin,” says Cuffe.

Chief Executive Owen Keegan has appointed new area engineers to deal with those queries, he said. The council could improve how it explains what it’s doing, though, says Cuffe.

“Often it’s a conflict between somebody saying, ‘I can’t turn here. Why does it take so long to get through these lights in my car?’ and somebody else saying, ‘I don’t have enough time to get across the street with my elderly father,'” he says.

Steady Flows

Hooked up to 380 camera across the city, the traffic controllers keep a constant eye on Dublin’s traffic.

The cost of smart systems like SCATS is ongoing. “What we’re trying to do is save time,” says Hosie. “That’s the main way we measure progress.”

The overriding aim of coordinated traffic systems is to prevent stop-starting whereby motorists stop their engine and have to restart. This just adds to the city’s congestion, says Hosie.

The recently introduced “bus gate” at Bachelor’s Walk, where there are now two lanes for buses, has led to a decrease in bus delays.

“So if we can decrease the delay time in buses, we can overall reduce the number of buses that we need because no bus gets delayed,” she said.

While technology may allow Dublin a dynamic traffic system, the Green Party’s Cuffe favours more hard engineering going forward, “so we’re not completely dependent on traffic signals and computers to sort everything out”, he says.

That means more space for public transport and cycling, which would also ease congestion. “But, touch wood, on the quays it seems to have worked out well,” he says. “I haven’t got a huge amount of complaints from car drivers.”

The planned December launch of the Luas should also ease congestion in the city, says Hosie. “We’re trying to ensure that public-transport users and pedestrians have a uniformed time for their travel,” she says.

In other words, if you think your journey takes 20 minutes, that’s what you should always get.


Cónal Thomas: Cónal Thomas is a city reporter for Dublin Inquirer.

Reader responses

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at 27 September 2017 at 22:31

All very well claiming pedestrians are top priority but they continue to have the longest wait time in Europe for a green man – nearly two minutes at every junction in Dublin. The wait time that SCATS imposes is totally unsuitable for central Dublin. And that’s just to cross one arm of a junction. This is why everybody jaywalks in Dublin.

at 28 September 2017 at 00:22

Great idea for an article. I wonder this on a daily basis. Getting around Dublin as a pedestrian feels laborious and unnatural – almost like pedestrians weren’t part of the plan. I often wonder how much of it is soluble with traffic management and how much of it is down to hard engineering. For me Dublin never feels like it all lines up as an integrated system. It feels as though whether you’re a car, a bike or a pedestrian – if you’re travelling from point A to point B – and there are 6 sets of traffic lights, you can be sure you’ll spend some time waiting at all 6 of them. Again I’m not sure how much of this is down to traffic management and how much of it is just a reality of the physical layout of Dublin.

at 17 January 2018 at 09:23

“Because the pedestrian takes priority in Dublin’s traffic system – followed by cyclists and then vehicles…”

HAHAHAHAHAHAHA! Slapping my thigh and wiping the tears of hilarity from my face here – ah, they said real comedy was dead! More of this, please!

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