Traffic lights for on-ramps to motorway

Traffic lights will appear on all Auckland motorway on-ramps, and possibly elsewhere around the country, to ration vehicle flows in what could prove a highly controversial scheme to fight congestion.

Transit New Zealand intends replicating throughout the Auckland motorway network a trial of "ramp-metering" which has run for nine months with mixed success at Mangere Bridge.

The lights will be linked to electronic vehicle sensors embedded upstream in motorways at 500m intervals, and traffic information will also be relayed to motorists to help them plan routes and travel times - even to the point of weighing up whether a trip is needed at all.

They will be notified by electronic road signs backed by radio bulletins, the internet and cellphone text messages similar to those sent to Auckland train passengers warning them of delays.

Variable speed limits on motorways are also being considered in a project due to be rolled out progressively over the next two years.

An investigation contract has been let to local and overseas consultants ahead of design and construction work due to start on the Southern, Northern and Northwestern Motorways next year at an overall cost of at least $26 million.

Transit expects benefits from reduced traffic delays of $22 for every $1 invested, and will eventually also add metering to the Southwestern Motorway, soon to be extended by 4km in each direction.

Similar so-called travel demand management (TDM) tools envisaged by the Government under the year-old Land Transport Management Act are being considered for other regions such as Bay of Plenty and Wellington.

Variable limits notified by electronic signs and enforced by speed cameras are already applied to the motorway through Ngauranga Gorge, Wellington.

The Manukau City Council's transport committee was warned last night that the Auckland project could prove highly risky and controversial, even if implemented well.

"It is a major initiative which will affect virtually every Aucklander," transport manager Chris Freke said in a report to councillors.

He pointed to mixed results from the trial at the Rimu St on-ramp at Mangere Bridge, in which vehicles have to queue in double lines at traffic lights to get on the Southwestern Motorway at peak times.

Although it had "probably resulted in some network efficiencies", he said the intent was to make access to motorways more difficult during periods of congestion.

The trial had also prompted traffic to try to cut into queues from a previously quiet suburban street, Crawford Ave, and buses became snarled in delays.

But Transit says waits of up to 18 minutes to get on the motorway early in the trial have been cut to a maximum of four minutes, now that motorists from suburbs further south have been discouraged from "rat-running" through Mangere Bridge.

Traffic lights allow two cars each to join the motorway at intervals of seven to 13 seconds at peak times, and there are plans to allow buses free passage past the queues, on an outside lane along Rimu St.

Transit travel demand project director Peter McCombs disagrees with Mr Freke's fear of a public backlash.

"I think the average person in the street will think it's about time," he said yesterday, adding that Transit was consulting all Auckland councils and would keep the public informed about the project through a planned website.

"It probably should have happened years ago - drivers out there are looking for leadership and management in making motorways work."

Mr McCombs said the Government was insistent about the need to manage travel demand, and the days were over when Transit simply cut a ribbon on a new motorway then turned it over to motorists to use to the point of gridlock.

"Our aim is to establish active management of the motorway network."

But he said Transit was also keen to collaborate with local authorities on the management of wider roading networks feeding or accepting traffic from motorways.

He pointed to congestion fuelled by queues to leave motorways, such as at the Greville Rd off-ramp to Albany, where traffic was held up by an uncontrolled roundabout.

He said the aim was to make travel times more consistent so motorists could plan daily activities with greater confidence.

Motorist now face delays of more than four minutes a kilometre on some sections of the Southern Motorway, causing serious losses in productivity and air quality.

Mr McCombs said ramp-metering was common in the United States and in parts of Britain and Australia.

Mr Freke said Transit could run into difficulties gaining support for a wider agenda of regulating access to motorways.

RAMP METERING

Electronic message signs are triggered when sensors indicate traffic on the on-ramp and motorway has exceeded a threshold

Traffic lights restrict traffic from on-ramps moving on to the motorway

System operates until sensors - every 500m - show traffic has diminished.