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Ask Phoebe: Car-speed indicators are easily confused

By Phoebe Falconer

17 comments

Discrepancy due to device giving speed of slower vehicle.

Photo / APN
Photo / APN

How accurate are the several speed sensors around Auckland and further afield? I have a late model car without modification and all the sensors I pass report my speed at 10 per cent under that shown on my speedometer. Practically everyone in Auckland drives at 60km/h, and when I am in a flow doing that speed (according to my speedometer) all the sensors I pass show only 54km/h. The same discrepancy shows on the open road. Which is right, the sensors or my (and everyone else's) speedometer?

Alan Jenkinson, St Heliers.

Your speedometer is more likely to be correct, as those speed sensors are easily confused. The range of focus for the radar on the sensors is about 50m, so it can happen that one vehicle can be shown a certain speed when in fact the radar is picking up the speed from another, slower, vehicle.

The solar-panel speed indicators are maintained on a six-monthly basis and are recalibrated every 12 months.

Several times in West Auckland recently, I have seen safety camera vehicles in distinctive police livery. Would it be possible for you to explain the purpose of these vehicles?

Patrick Robertson, Glen Eden.

I think these are more likely to be speed cameras, but they do have a dual purpose.

According to the police website, speed cameras are sited where speed has been a significant factor in crashes or where there is an obvious road safety risk. Aggregates of the photos are used to monitor speeds, risks and trends over time and to inform future planning. The total photos per hour and per 100 vehicles are recorded for urban, rural and school zones.

Not sure if this is your field of interest, but in West Auckland we regularly used to get a vote (not sure if it was the general or local body elections) on how liquor was to be sold. I can't remember the last time we voted, but I'm sure it was not in the last two elections. Can you clarify the situation? Lois Leece, West Auckland.

My dear, everything is my field of interest. There are two distinct matters here. One is the voting for members of the trust every three years. This occurs in line with the local body election cycle.

The other is a vote or referendum for a review of trust areas. This referendum occurs only when it is forced by a minimum of 15 per cent of voters. You may remember that in 2003 supermarkets out west got enough electors to sign a petition forcing a referendum about selling of alcohol in supermarkets in the area. The trusts won.

I swim at Judges Bay and use the pontoons as distance markers. I am only guessing the distance in relation to time as I cannot find information on how far apart these are. Do you know how far apart the pontoons are and the distance the first one is from the jetty/steps? Alana Bebich, Auckland.

I am reliably informed that the pontoons are positioned at 50m intervals, with the first (landward) pontoon located approximately 50m off Judges Bay beach and 25m from the seaward extent of the pier steps.

- NZ Herald

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