It was a rain-sodden Wednesday in November and outbound traffic on the N11 had become compressed into a long, stalled mess. With just one lane taking traffic past emergency roadworks near Bray, thousands of drivers became trapped. For hours. The system had ground to a halt.
Cars were abandoned, others ran out of fuel. The following day, radio phone-ins were jammed with angry motorists relating tales of horrendous five-hour journeys home.
To prevent chaos like that on the roads inside the M50 loop, Dublin City Council has gradually developed a sophisticated traffic management system. Unfortunately for the motorists stuck on the N11 that day, the system does not cover the N11 as it ends at the M50.
Controllers in the council traffic management centre onWood Quay were unable to see the scale of congestion until the tailbacks became visible on cameras overlooking the point that the M50 and N11 roads merge.
Brendan O'Brien, head of technical services with Dublin City Council, says that had a network of cameras, centrally controlled traffic lights and ground sensors been available on the N11, it would have been possible to alleviate the congestion.
"The reason such congestion could develop and the City Council was largely unable to counter it was simply because the cameras and centrally controlled lights integral to the council's traffic management system are not on that section of the N11.
"The area affected is about 10 miles outside the city council area. Wicklow County Council were responsible for the traffic control on the ground."
O'Brien says the fact 500,000 vehicles can enter Dublin city each day, whilst major projects like Luas and the Port Tunnel were being built and the M50 upgraded, without similar congestion, shows the effectiveness of the city's traffic management system.
However, while the system covers the city centre, M50 and the city's busiest route, the M1, it does not stretch along the major approach roads into other council areas.
He says the system is likely to be extended, particularly around some of the new junctions off the M50 and, in time, may also cover part of the N11.
Keeping half a million vehicles trundling through Dublin is a daily challenge for the controllers at the traffic centre.
Helping them in their task are 130 cameras that traffic centre staff monitor live on a wall of TV screens. Another screen shows the inside of the Port Tunnel.
At their desks, computer screens carry details of traffic flows through individual junctions based on ground sensors that track the number of vehicles. Data from 550 junctions feeds into the Sydney Co-ordinated Adaptive Traffic System (SCATS), the traffic management system used by the council.
This programme makes incremental adjustments to traffic light timings based on minute-by-minute changes in vehicle flow at each intersection. For example, if the time between vehicles travelling through a junction is increasing, traffic is relatively light, so the system seeks to reallocate "green time" to where need is greatest.
Given its name, it is no surprise to learn the traffic management system originated in Sydney, and it now is also used in Melbourne and Hong Kong.
"Nobody is disguising the fact that there is traffic congestion and traffic problems, but you have to look at the growth in traffic in Dublin. It's a couple of per cent a year. The fact that the city has kept functioning is attributable to these kinds of systems," O'Brien says.
However, he admits the city is at capacity. "On a normal day, there is congestion. But even if there is a relatively minor incident, a crash or a breakdown at an important junction, that can cause huge disruption very quickly. People are surprised at how it causes such long delays, but there is very little spare capacity if one major route is blocked."
The SCATS system has preloaded responses to problems at certain junctions and can also give green light preference to assist an emergency vehicle trying to get through the city.
The controllers working around the clock at the centre also update a series of roadside and overhead electronic signs to alert drivers to specific issues on the road ahead.
As part of its traffic management, Dublin City Council also funds Livedrive radio (broadcasting on 103.2FM), which supplies journey information based on the situation available from the cameras. This system also feeds the AA Roadwatch reports.
Given the size of the city and the never-ending roadworks, on any given day, one or more of the council's sensors may be off-line. To minimise downtime, the council pays almost €3.5 million for an engineering company to provide round-the-clock repair service for the traffic lights, cameras and ground sensors.
"We control all road works and have clear controls around who can carry out works and when. All roads are graded from one to five, with one being a housing estate road. On some roads, we can only work at night or weekends," says O'Brien. He adds that the contractor is liable for all damage to the road surface and the sensors under it.
The council hopes to connect another 50 to 60 junctions to SCATS in the coming year and, as part of the M50 upgrade, it is also looking at installing traffic monitoring equipment at approach roads in Fingal.
Footage from the cameras is not recorded, but the live feeds are linked to Garda HQ, principally for traffic management policing. Traffic controllers can also use the footage to request a clamper or tow-away truck deal with a parked vehicle causing an obstruction. The parking control firm does not have direct access to the camera feeds.
O'Brien expects further restrictions on vehicle access to parts of the city in the future, pointing to the reorganisation of O'Connell Street and the banning of five-axle trucks, which produced more gridlock this week, as examples. Investment is focused on public transport projects rather than new roads, he said.
Aside from shuffling half-a-million vehicles through some of Dublin's Viking-era streets, the traffic management system has also helped Dublin City Council to reduce fatal crashes.
"The number of fatalities in the council area is now around 15 to 16 a year, down from a high of 53," says O'Brien. "In 1997, there were 615 people seriously injured, and in 2003, that was down to 276 and would have continued on down."
The council ranks the top 10 collision sites each year and then changes junctions to make them safer, often after reviewing their performance on the cameras.
Including the outside contractors and the radio broadcasts, the system costs €4.5 million a year. It has been installed incrementally, but would cost up to €50 million if installed from scratch.
For a motorist sitting in congestion today, sceptical about the benefits gained for this outlay, the daily impact of the system is "a 10 to 20 per cent increase in vehicle capacity on Dublin streets every day," says O'Brien.
Make the most of the system
• Motorists can register for e-mail or text alerts of congestion on their regular route at www.dublinregionaltraffic.ie
• Dublin City Council provides realtime traffic information online using a colour-coding system to congestion. Camera images and details on parking are also available at www.dublintraffic.com
