Stuart Williamson, of Dunedin, asks :-

Where does all the rubber dust/particles go worn from rubber tyres wearing out on our roads?

Mofreh Saleh, a roading specialist at the University of Canterbury's Department of Civil and Natural Resources Engineering, responded.

The rubber and dust materials that are generated due to the continuous wear and tear in the tyres and the road surface are either air born and transported to the road sides or other surrounding areas or washed out by rain and get deposited onto road side ditches. Some of these contaminants such as cadmium, zinc or lead might infiltrate into the ground water table.

New tyres usually last between 40,000 to 80,000 km of travel but this will also depend on the tyre quality, road condition, driving, weather condition and road geometry. The tyre inflation pressure is an important factor and it must be properly and regularly checked. Using lower or higher tyre pressures will create a different stress distribution that shorten the service life of the tyres. It is also important to rotate tyres regularly by bringing the front tyres to the back and vice versa and also shift sides from right to left and vice versa to make sure that there is uniform wear and tear. I believe HOT MIX Asphalt surfaces are more friendly surfaces compared to chip seals surfaces.

The other question not asked but which might be of interest to know about is that every year there are millions of old tyres that we throw away which raises the question what could we do with these old tyres? In Pavement Engineering which is part of the Civil Engineering discipline we do a lot of research to promote recycling and one of these materials that we recycle is old tyres, which can be shredded by special machines into different sizes called crumb rubber. Crumb rubber can then be added to the bitumen to improve the performance of asphalt mixes; for example crumb rubber can improve thermal characteristics of asphaltic materials and therefore reduce thermal cracking of road pavements. In addition, crumb rubber can improves flexibility and fatigue resistance of asphaltic materials therefore extending its service life.