CPX NOISE MEASUREMENTS	03/01/2007
	CARL BRO measures the noise Noise is an increasing problem for many people living next to heavily trafficked roads. Removing the traffic would result in very high costs, and thus the solution is to remove a considerable amount of the noise by means of a new low noise pavement. Grontmij | Carl Bro is now capable of measuring the effect of the noise reduction solutions. The Close-Proximity Method (CPX) measures the noise emission from a standard passenger car tyre when rolling over a road surface. The CPX measurement is described in the ISO standard ISO/CD 11819-2 and is performed in accordance with this standard. Grontmij | Carl Bro offers these measurements in cooperation with a Dutch company having a closed CPX trailer for measuring of roads and software for data treatment and presentation of the results. In the closed and noise isolated CPX trailer several microphones are mounted close to the test tyres recording the noise emission from the tyres. Inside the trailer is mounted a tyre from a passenger car and a truck respectively, and separate measurements are made on the tyres simultaneously. Depending on speed limitations measurements are made at a constant speed of 50 km/h or 80 km/h. Normally, measurements are not performed at other speeds. In this way the option of comparison with other road sections is preserved. Measuring on road sections with road bumps, crossings and other obstacles is very difficult, as it is not possible to keep a constant speed on these sections. Measurements on a section are performed only in one direction as this is normally representative for the entire road. The surface measured must be entirely dry. It is impossible to measure in or after rain, as the results will be useless. The results of the measurements are normally treated in 20 m segments. This is the reason why measurements should not be performed on road sections shorter than 100 m and the upper limit is 3,000 m. The raw measuring data is normalised to the given speed and temperature corrected. The final result of the CPX measurement is a CPX noise level for the standard passenger car tyre and the truck tyre, respectively, and a common index (CPXI). This will be part of the final reporting where a conversion of CPX values to SPB values (Statistical Pass-By) is made on the basis of the CPX measurements made on Dutch reference sections. This is an expression of the average noise observed by a person at a distance of 7.5 meters from the centre of the road, when a vehicle passes by at a given speed. Furthermore, Grontmij | Carl Bro offers measurements on reference sections with AB 11t and/or AB 8t where interested parties share the costs. All interested parties are offered a common and anonymous survey with comparison of the sections selected by the participants. Such measurements will allow control of the noise emission from an existing or newly paved wearing course and it will be possible to assess the effect of a new wearing course. Moreover, it would be an easy and efficient way to measure the noise emission from very heavily noise loaded road sections. On the basis of the calibration of the CPX measurements on reference sections it is very easy to assess the SPB noise level of the road. This is a far less expensive way than having direct SPB noise measurements carried out. In order to be able to perform the measurements, the following information should be known: • Road name (e.g. road no. and route no.) • Start chainage (typically a road name and a unique terrain object) • Kilometre counting (from and to chainage or between two roads) • Existing wearing course type (e.g. AB 8t and OB 5/8) • Paving year