Standing next to a busy highway, most noise comes from car tyres. Is there any way to reduce this noise while keeping the more desirable properties of tyres, such as traction?
鈥� The noise comes from tyres鈥� interaction with the road surface. Hence the nature of the surface can make a big difference to the noise produced. Many motorways in my native country, the Netherlands, are being surfaced with ZOAB, the Dutch acronym for very open asphalt concrete. The surface鈥檚 high porosity allows sound to dissipate downwards, as well as upwards and sideways, creating markedly less noise. The dampening effect is noticeable both outside and inside vehicles. Another advantage is a reduction in spray in wet conditions.
Traction is deemed to be acceptable on these surfaces, but is reduced compared with typical road surfaces, especially when the ZOAB is new. That鈥檚 why you will see signs saying 鈥渘ew road surface; increased braking distance鈥� along recently surfaced stretches of these motorways.
Advertisement
The other downside is the increased need for salting in winter. The wet nooks and crannies in the ZOAB surface are perfect hidey-holes for ice. These road surfaces break up more easily as well, and need to be relaid more frequently than solid asphalt.
Jan Meulendijk, Haverfordwest, Pembrokeshire, UK
鈥� There has been a great deal of research into this topic in the EU over the past 20 years. During the time I worked on traffic noise at the UK鈥檚 Highways Agency, a range of quieter surfaces were developed. Long-term trials were undertaken to monitor their resistance to wear and skidding performance, as well as the amount of noise emitted in a standard roadside test.
Part of the problem arises as tyres interact with surfaces that are deliberately roughened to improve skidding resistance. Concrete has been used extensively in the US because it is durable and economical for long stretches of road, but it is difficult to create smooth rolling surfaces in concrete while ensuring the right texture for good skidding resistance.
鈥淐oncrete is durable but it is difficult to create smooth rolling road surfaces with good skidding resistance鈥�
Efforts have been made in the US to retexture some older concrete roads using diamond saws to cut longitudinal slots in the surface, which help to disperse water. This doesn鈥檛 necessarily generate as much tyre noise as the transverse-brushing process that has been used to provide skid resistance on concrete roads in the UK. However, sawing and regrinding concrete is a slow and expensive process.
Peter Kinsey, Llangybi, Monmouthshire, UK
This article appeared in print under the headline 鈥淭ired tyres鈥�