Ask Phoebe: Motorway time boards meant as early warning

When complete, the system will have 250 signs, at a cost of $3 million. Photo / Natalie Slade

I regularly travel on the Northwestern Motorway in the morning, passing a sign on Great North Rd just before the onramp which advises that the travelling time to Nelson St is, for example, eight minutes. In fact, it takes longer than eight minutes even to get on to the motorway, since you have to queue for the lights. It may then take another eight minutes to reach Nelson St. Why is this time displayed, when it is so misleading? Presumably all the other times are also wrong. Eileen Howard, New Lynn.

The Transport Agency put the signs up to provide expected journey times for key destinations using a motorway. The time displayed is the expected time on the motorway itself, not on the approach roads.

The siting of a sign and the time of day, such as morning and evening peaks, mean that the time it takes to actually get on to the motorway can vary. The signs are in locations that give drivers time to decide whether they want to use the motorway or take an alternative route using arterial roads.

The system uses data from detectors placed every 500m along motorway lanes to measure current running speeds, density and volume and is updated every 30 seconds. This allegedly gives a margin of error of four minutes for a typical 25-minute motorway trip. Early reports indicated a reasonable level of driver satisfaction.

When complete, the system will have 250 signs, at a cost of $3 million.

I frequently travel on the Northern Motorway and have found a real puzzler. Heading north, just past the Silverdale interchange, the road sign shows the distance to Whangarei as 140km. If you drive another 4km or so to just past the Orewa interchange, the distance is given as 123km. Where have the other 13km gone? Ken Carter, Whangarei.

Whoops. The 140km sign was put there when the old State Highway 1 went through Orewa and Waiwera. Since the advent of the Northern Gateway Toll Road, which bypasses Orewa, the distance is reduced. The sign at Silverdale will be changed to read 127km.

I travel to work each morning on the bus from the North Shore. At the bottom of the Auckland Harbour Bridge on the city side, a new lane is being developed. Is this going to be a new bus lane? When will it be finished and ready for use? Will we have to wait for the Victoria Park tunnel project to be completed before the bus lane opens? Noelene Wallace, North Shore.

The lanes you see being built are a fifth lane for general traffic and a shoulder lane for buses, to help ease congestion.

Because of the need to provide a safe environment for workers on the Victoria Park project, as well as motorists, general traffic will get first shot at the lanes until widening work in St Marys Bay and the tunnel links are completed. The dedicated bus lane will open as soon as it is safe to do so - probably not until early 2012.