PolyU researchers seek to calm noise on the road

According to the Principal Investigator Dr Hung Wing-tat, Associate Professor of PolyU's Department of Civil and Structural Engineering. The study is made possible with the set up of a sophisticated machine known as the Close-proximity (CPX) Trailer.

While traditional measurement of road traffic noise is done along the roadside, the CPX Trailer enables researchers to measure tyre-road noise on the road with its unique set up.

“The major merit of the CPX method is its ability to delineate the tyre-road noise from the background and thus enable engineers to fully assess the noise reduction effect of various types of low noise materials for road surfacing as well as low noise tyres,” said Dr Hung, who is also Researcher of the University's Hong Kong Road Research Laboratory based in Whitehead of Ma On Shan.

The CPX Trailer was set up with initial funding support from the Environmental Conservation and Wheelock Green Fund. Towed by a four-wheel drive 2300 cc saloon car, the trailer contains an acoustic enclosure covering the test tyre and built in with a video-recording camera and two microphones. More importantly, this trailer is tailored to meet the stringent certification requirements of noise measurement and to run on narrow roads in urban areas of Hong Kong.

During the past three years, Dr Hung and his team have been using this CPX Trailer to collect valuable data on tyre-road noise in 66 road sections of the territory – very often in the middle of the night. They have reviewed massive data and examined the effects of different factors including driving speed; type of road surface; polymer modified surface; aggregate size and layer thickness; and the choice of tyre on tyre-road noise.

Their study found that tyre-road noise level increases significantly (over 3dB) when the vehicle speed increases from 50 km/hr to 70 km/hr. They also found that the smaller the stone size on road surface and the thicker the layer, the quieter is the road surface at low speed driving (with a difference of 6 dB at 50km/hr). At a reference speed of 70 km/hr, concrete road is the nosiest. The total volume of air void in the pavement surfacing also appears to have an impact on noise reduction.

According to EPD statistics, more than one million Hong Kong people are irritated by road traffic noise of over 70 dB per hour. In the next stage of study, PolyU has been further supported by a HK$1.77 million grant from the Environment and Conservation Fund to develop a new, fully automated CPX vehicle to upgrade the existing Trailer in measuring tyre-road noise. PolyU researchers will also probe the effectiveness of low noise tyre and the resurfacing of low noise surfacing materials at the same time.

The University will be conducting a series of territory-wide road tests to identify low noise road surfaces and tyres in collaboration with the Highways Department and EPD after the newly design CPX vehicle has been fitted and set up to satisfy all related ISO certification requirements.