KEY POINTS:
Traffic lights and sensing equipment aimed at making vehicles flow better throughout Auckland's motorway network are expected to cost as much as $70 million.
The director of Transit NZ's "travel demand" project, Peter McCombs, told the Auckland Regional Land Transport Committee this week that his organisation had gained
Government funding approval to add the western ring route to its ambitious signalling scheme previously costed at around $50 million.
That means traffic will ultimately be governed by signals on 91 approaches to the ring route and Auckland's three other motorways.
Capital costs will include adding priority lanes to 15 of the on-ramps, which trucks, buses and other vehicles with more than one occupant will be entitled to use to bypass the signals.
Mr McCombs assured committee members that the impact of longer traffic queues on local roads would be outweighed by better-flowing motorways. Transit already operates signals on six motorway on-ramps, including a test set installed at Mangere Bridge in 2004 with mixed results.
Five other sets were installed over summer on the Southern Motorway, including two around Spaghetti Junction and another on the ramp carrying traffic from Curran Street to the harbour bridge.
Mr McCombs said 31 on-ramps to the Southern Motorway would be fitted with signals by April, and 30 others on the Northern and Northwestern motorways by early 2009. Another 30 would be installed along the western ring route between Manukau and Albany as it was being built.
He said signals were switched on only at times when they were likely to improve motorway traffic flows but those at Curran St had improved minimum traffic speeds on the harbour bridge's outside clip-on lane by 13km/h in afternoon travel peaks.
They had also boosted the lane's carrying capacity by about 18 per cent, or 180 vehicles an hour, and allowed tow trucks to clear smashed vehicles or other obstacles up to 15 minutes faster than before the signals were installed.
Waiting times for traffic queuing on Curran St signals averaged 2.8 minutes, and Transit had begun using the signals in the morning travel peak as well, to tackle increasing congestion. Mr McCombs acknowledged that this compared with about 20 seconds spent by vehicles joining motorways without waiting for signals, but said the extra time was offset "by the gains you get on a big asset on the Auckland network".
"It's a matter of balance," he told the transport committee.
Committee member Kathleen Ryan, representing environmental sustainability interests, wondered about added air pollution in local streets from traffic waiting to join the motorways. But Mr McCombs said overseas "ramp-signalling" schemes usually generated carbon credits "and we expect to achieve similar benefits here".
He said Transit was working closely with Auckland City Council to monitor and improve the system, and to encourage more traffic to use the non-signalled northbound on-ramp from Fanshawe St.
That mainly included traffic which previously joined the motorway from Wellington St, where he acknowledged delays at the lights had been "in people's faces" at times.
He said the average waiting time at Wellington St was 2.5 minutes.
Transit has a written agreement with Auckland City and other local authorities to turn off the signals if traffic congestion becomes unacceptable in local streets.
But Auckland City roads manager Matthew Rednall said his council was working with Transit to ensure the provision did not have to be invoked.
That included fine-tuning the system, such as altering signalling phases and remarking entry lanes to on-ramps.
