Ramp signals for more of Auckland's motorways

NZTA ramp signal engineer Kevan Fleckney at the Queen St control centre. Photo / Brett Phibbs

Ramp signals have improved travel speeds on Auckland's Southern Motorway, North Shore councillors were told yesterday as they agreed to their use in their city.

But NZ Transport Agency officials could not convince all North Shore City Council members yesterday of the benefits of switching on the first ramp signals for the Northern Motorway from some time between May and August. They were installed on the Southern Motorway in 2007.

The agency's claims of faster travel speeds since and of a 5 to 15 per cent increase in the rate of flow of vehicles were dismissed by councillor Jan O'Connor.

She said Takapuna commuters queued daily in Esmonde Rd for 15 to 20 minutes trying to get on the motorway to work in Auckland City.

In the morning peak, 12,000 vehicles an hour tried to enter the motorway from Esmonde Rd.

"People are saying our on-ramps are too short to get a speed up and they 'ride the red' signal.

"There's nobody enforcing riding the reds and we want proof that signals won't lead to greater queues."

Mrs O'Connor moved to have the agency defer putting in signals at the 12 sites proposed until it gave evidence that the system would not worsen queues for Northern Motorway on-ramps and congestion on local roads.

Her motion was defeated by nine votes to five, although many councillors agreed the signals would become a hot topic for residents.

Peter McCombs, the transport agency's ramp signalling project director, assured councillors it had an agreement to switch off the signals if side roads choked up.

However, he said the signals would manage merging traffic which caused the morning's motorway traffic to back up to Greville Rd.

On-ramp peak volumes in the central area typically increased by 100 to 140 vehicles an hour compared with before ramp signals were commissioned.

A 15 per cent improvement in motorway mainline traffic flow speed was equivalent to an extra 600 to 800 vehicles an hour that could use the motorway. "There are still some periods when all of the network is overwhelmed by sheer volumes of traffic," said Mr McCombs. "But the onset of severe congestion is avoided by up to 30 minutes and recovery is achieved earlier than before."

Onewa Rd traffic will not face the signals, which will be installed elsewhere in groups.

Northbound ramps for Esmonde Rd, Northcote and Tristram will be commissioned before the southbound ramps for those roads.

Upper Harbour Highway northbound signals will start in June to be followed in August by the southbound ramps for Constellation Dr, Greville Rd and Oteha Valley.

Yesterday, in a Queen St control room, signal system operators had information from traffic detectors in the motorway lanes, on- and off-ramps and arterial approaches, as well as real-time views supplied by 220 cameras. The system continually monitors traffic movements both on the motorway and adjoining roads. It turns the ramp signals on when it detects signs of worsening traffic flow.

Ramp signal timings are continually adjusted to reduce delays on arterials. If queue lengths grow at any ramp, the system increases the discharge rate to compensate and calls on help from the next upstream ramps.

RIGHT SIGNALS

Southern: 31 sites operating.
Northwestern: Five operating, four more ready to go, remaining six from next month.
Northern: installation under way for 12 ramps, commissioning from May-August.
Western Ring Route (SH20), commissioning Mt Roskill over next few months.