TOLL road operator Transurban has apologised for what it described as the worst traffic failure in its 13 years operating CityLink, but could not guarantee that yesterday's computer malfunction, which forced it to shut down Melbourne's two busiest road tunnels for most of the day, would not happen again.
By late yesterday Transurban had not yet identified what caused its computer system to fail in the early hours of the morning, meaning the sprinkler and smoke extraction systems in the Domain and Burnley tunnels would not work.
The malfunction was quickly deemed a big enough threat to public safety to close the tunnels completely. Tens of thousands of vehicles were diverted onto other roads from before the morning peak until after 4pm, causing long traffic delays. Motorists reported delays of up to two hours during their morning commute.
The two tunnels are used by 120,000 vehicles each weekday and are part of the M1, which is Melbourne's busiest road and a main freight route. The meltdown, which caused most of those vehicles to be diverted before the tunnel was re-opened to lighter afternoon peak-hour traffic, provoked debate about how to end the city's reliance on one main east-west road across the Yarra River.
Tens of thousands of tram passengers were also dragged into the inner-city gridlock, with six tram routes experiencing delays of between 15 minutes and an hour.
The meltdown came at an unfortunate time for parent company Transurban, which already faces a shareholder revolt over generous executive salaries at its annual general meeting this morning.
Former Transurban chief executive Chris Lynch, who stepped down in July, received a total remuneration package of $7.36 million in the 2011-12 financial year - up from $6.75 million the year before, according to the company's full-year reports.
Australian Shareholders' Association chief executive Vas Kolesnikoff said the salary was exceptionally large given the company's performance. ''Seven million is a large amount of money for collecting tolls,'' he said.
Scott Charlton, who replaced Mr Lynch as chief executive, admitted CityLink's computer safety system had been hit by ''failure on failure'', with a communications fault at 4.10am being quickly followed by the failure of the back-up IT system.
Technicians worked for 20 minutes to fix the fault, before a call was made at 4.30am to close the tunnels. They did not reopen for another 12 hours, and even then only in a limited capacity, with two lanes open in each tunnel and speed restrictions in place for the evening peak.
''The decision to close the tunnels was not taken lightly and was based on safety being our number one priority,'' Mr Charlton said.
''If an issue were to occur in one of the tunnels, a fire or something, we didn't have confidence that we would be able to use the systems properly.''
He apologised to motorists.
''This tunnel outage is not acceptable and we appreciate the significant impact it's had on Melbourne and we agree with the Premier [Ted Baillieu] that this should not happen again,'' Mr Charlton said, but he could not guarantee that it would not recur.
The Bureau of Transport and Regional Economics estimated in 2008 that traffic delays in Melbourne cost the economy about $2.7 billion a year.
Public Transport Users Association president Daniel Bowen said the fact trams were sucked into the chaos proved the need to give them a better run at intersections, given the number of passengers each can carry.
''It's really unfortunate that trams that might be carrying 100 or 200 people are stuck in the traffic with cars carrying one or two people,'' Mr Bowen said.
''Traffic light priority alone could improve tram travel times by about 20 per cent.''
With Vince Chadwick and Georgia Wilkins