Ask Phoebe: Watchers ensure ramp signals go with the flow

What dictates whether onramp signals are switched on or not. The difference in motorway traffic at the start of the Northwestern heading west is dramatic, depending on whether the signals are on or not. Is there any rhyme or reason to not turning them on? Rachel Harrison, West Auckland.

The Transport Agency says that the ramp signal system responds to traffic conditions, measured by detectors along the motorway lanes, on nearby arterial roads and on the ramps themselves.

The signals are constantly monitored by operators who watch pictures taken by cameras around the motorway system and who also have access to extensive real-time data.

The signals turn on when the system detects signs of slowing traffic and/or an increasing number of vehicles, which are the first signs of congestion. This may be at one ramp, or may happen at interchanges further downstream on the motorway.

Ramp signals operate only for as long as they are needed. They turn off as traffic flows clear along a section of motorway, and will run only for as long as it takes to restore free-flowing traffic. They may be on for only a few minutes if that is all it takes to get back to normal flows.

As a commuter who uses Hillsborough Rd, my own unscientific estimate is that traffic on that road has dropped by about 30 per cent at peak times, since SH20 opened.

Does any Government body survey traffic volumes on arterial routes after the completion of major projects and, if so, what is the percentage drop in traffic on Hillsborough Rd? Terry Henderson, Hillsborough.

Your unscientific survey is right on the money. The Auckland City Council does traffic surveys on arterial roads throughout the isthmus every year, and the drop in two-way traffic on Hillsborough Rd during morning and afternoon peaks since the opening of SH20 is 30 per cent.

The survey was done near the Cape Horn Rd intersection in July last year.

Surveys of other arterial roads running parallel to SH20 have also indicated significant drops in traffic volumes.

You can find the data on traffic flows on the council website at www.aucklandcity.govt.nz

Why have the newly installed drinking water points been removed from Freyberg Place? They were such a good idea, as people could fill their water bottles or have a drink from the spout at the other side. Pat Collings, Auckland Central.

It was a trial fountain installed by Metrowater which borrowed the idea from similar models in Sydney. The fountains are also vandalism resistant, hygienic and child and wheelchair-user friendly.

The plan was to see if people liked the fountain. If they did, more might be installed. Since the one and only has gone, it seems we didn't like it enough.

* A police contact tells me that motorists do get ticketed for using fog lights when they shouldn't, but most of the time police officers find that people don't know how to operate their lights, so they get a verbal warning and an instruction to turn them off.