Road-surfacing choice

Press, Volume CXII, Issue 32977, 25 July 1972, Page 15

Road-surfacing choice

Provided vehicles are fitted with good tyres no skidding problems should arise in 30 miles-an-hour areas on wet roads with surfaces of non-polishing aggregate, says the City Engineer (Mr P. G. Scoular) in reply to a letter to “The Press.”

A correspondent, "Concerned Motorist,” wrote: “As our roads are occasionally improved, tidied, and resealed, could someone tell me why the new surfaces are made so smooth? They look nice and sound nice, and are easy to drive on; but only on a dry day. On a wet day, even at 30 m.p.h. and less, a sudden braking stop leads to a skid, and this on good new tyres. On a wet black night

we have a dead surface—almost like driving into outer space. Perhaps this surface is cheaper than the rough sealing we used to have, but does this lielp when someone has skidded into you or you have gene into the path of an oneeming car because your fjwes cannot get a grip? Perhaps it does not happen all the time, but it is a nasty feeling when you are forced to an abrupt stop and find your car doing a skating ballet.” MAIN ADVANTAGE Mr Scoular said that the main advantage of the dense graded, bituminous road-sur-facing used in Christchurch streets was that it produced a smooth-riding, skid-resis-tant surface capable of carrying heavy traffic volumes with lifnited or no maintenance needed for 20 or 30 years.

‘lt is designed so that the relationship between asphalt content and aggregate grading is kept within very close limits to provide a mix that is both dense and stable, and, at the same time, contain sufficient voids to prevent the asphalt binder working to the surface under traffic to produce a fat or bleeding surface which could cause skidding. “It is acknowledged that the wet-night visibility of normal road markings on these surfaces is not good, but some raised button-type reflective markers are being tried, as an experiment, and the National Roads Board requires this type of marking on State highways. “Normal chip resealing is not entirely satisfactory for busy city intersections where turning, braking and accelerating traffic subject the binder film to excessive stresses, producing stripping of chip and consequently bare patches of binder. “Alternatively, if more binder is used the traffic will soon 'fat up* the surface to produce a smooth and dangerous surface. Should ‘Concerned Motorist’ care to provide details of the location of his skid, the matter will be further investigated,” said Mr Scoular.