Ask Phoebe: How to work out steepness of our streets

The percentage refers to the steepness of the road.

Though a complex-sounding calculation, slope angle is just altitude change over distance.

Would you be so kind as to find out from NZTA what the percentage sign refers to on some of their steep hill gradient signs? 12 per cent of what? ... Surely not of a hundred! Simon Pickstone, Wellsford.

The percentage refers to the steepness of the road, and these signs bring us into line with road signage in Europe and Australia.

Trigonometrically, the sign is a measure of the tangent of the angle of inclination (or declination) from the horizontal, expressed as a percentage. In other words, it's the ratio of altitude change to horizontal distance covered.

Thus, if the sign reads 12 per cent, it means that for every 100m travelled (in a horizontal plane) you go up 12m.

I recall you being asked previously about when LTA intends to three-lane the Mt Wellington overpass on the Southern Motorway. The answer has always been that the bottleneck is designed to slow motorway traffic so that Mt Wellington traffic has an opportunity get on to the motorway. Is a 30-year-old strategy still appropriate given that the resulting tail on the Southern goes back 4-5km most mornings? Does LTA have anything at all planned for this overpass? Eric Wolters, Auckland.

The LTA (now the New Zealand Transport Agency) says most of the traffic build-up at Mt Wellington is due to existing congestion on the motorway north of this area at the SEART, Penrose, Ellerslie/Panmure and Greenlane onramps - not at Mt Wellington itself. The Government has announced a number of accelerated transport works for Auckland in the recent Budget. As part of that programme, the Transport Agency is looking at improvements to road connections in the Penrose/Onehunga area and on the Southern Motorway. Delivery of these works will have a positive impact on traffic around Mt Wellington. Longer term, the Transport Agency is investigating options further north on the motorway to make traffic flow more smoothly.

*To clarify an item about animals on public transport and in public places: I have been advised that under the Dog Control Act 1996 and its subsequent amendments there are currently six organisations who have dogs that can access all public places including public transport - these dogs are known as disability assist dogs. They are: Guide Dogs, Hearing Dogs for Deaf People New Zealand, New Zealand Epilepsy Assist Dogs Trust, Mobility Dogs, Perfect Partners Assistance Dogs Trust, and the Assistance Dogs New Zealand. All of these dogs have public access while in training, as well as when they are working with their handler once they are fully trained. I apologise for the error.

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