Q: Any idea how the NZ Transport Agency chooses the grade/type of asphalt to use? The asphalt on the motorways is smooth as silk, a pleasure to drive on, one can even listen to music. But the Mangatawhiri bypass built just a few years ago has very rough, noisy asphalt. You can't hear yourself think let alone hear music. The choice cannot be for better grip on the rougher surface, as the curves and hills on that bypass are gentler than many on the motorways. And our city streets are a hodgepodge. The smooth stuff is so much more pleasant for driving, so why not use it all the time? Ron Baker, Auckland.

A: As with so many things, Mr Baker, it's a matter of cost. The Transport Agency's highway network operations manager, Karen Boyt, says that asphalt surfacing (aggregate and bitumen laid by a machine) costs up to five times as much as chipseal surfacing (bitumen sprayed on to the road then covered with stones). Asphalt surfacing also lasts up to 10 years, whereas chipseal surfacing lasts between 5-7 years.

Thus asphalt is used on roads with heavy traffic volumes (such as motorways) and on some higher-volume intersections. The more commonly used chipseal is suited to roads with light to medium traffic volumes. Asphalt does provide a smoother and quieter surface in comparison with chipseal.

Q: Having travelled to Auckland over the recent long weekend I kept on seeing signs that indicated a distance to Auckland. These signs are of course all over our lovely land, giving distance to all our cities/towns. But, my question is, what is the distance to? The sign says Auckland, big place that! So, is there a standard place in all towns/cities where road distances are measured to? I'm told it's the post office but there are few of those any more. Can you help? John Laing, Welcome Bay.


A: Distances are now measured between the "recognised centre" of each town. In days gone by, this was traditionally the post office, as you note, but the closure of many of these in the 1980s created a difficulty, so now the centre of town is the start and finish point. Quite who decides where the centre of town remains unclear, and I would be delighted to hear from anyone who knows.

In Auckland, distances on the motorway are measured between offramps.