Description

Traffic noise can affect people’s health and comfort in areas close to the roads and it can lead to a negative impact on safety because of the tiredness of drivers.

Road traffic noise may be generated by power unit of vehicles (motor, brakes, exhaust pipes, etc.), aerodynamic friction or tyre-road surface interaction. At speeds of 50 km/h and upwards, this interaction is a major component of total noise. Two main mechanisms are recognized to have capital influence on this type of noise: air pumping by compression and expansion of air trapped between tyre and surface of road, together with tyre vibrations, and physical characteristics of pavement, such as texture (from 1 to 100 mm) and acoustic absorption (porosity).

From the point of view of construction and maintenance of roads, data of noise emission are very important to arrive at a quantitative ranking of road surfaces, in order to establish strategic plans for traffic noise reduction on roads close to urban areas.

Two general methods have been established for measuring the influence of road surfaces on traffic noise: The Statistical Pass-By standard method (ISO 11819-1), that uses microphones positioned close to the road, and a non standard method, the Close Proximity method (ISO/CD 11819-2). The latter uses two testing procedures: The investigatory method (at 50, 80 and 110 km/h) and the survey method (at 80 km/h).

In the CPX method, tyre-road noise is isolated from the rest of traffic noise. The CEDEX measurement equipment consists of a trailer supporting two semi-anechoic enclosures, each one covering a wheel with a reference tyre, two microphones in cach wheel, transducers for measurements of air and road surface temperature, distance and relative humidity of air.