Using lasers to measure the quality and condition of road surfaces
When the journey is smooth, very few drivers spare a thought for the wear and tear that the roads under their tyres are suffering. It is only when those surfaces begin to deteriorate and crack, and holes appear, that the constant stress the road network undergoes becomes an issue. In an ideal world drivers would never have to think about the state of the roads - because any deterioration would be detected by a non-obtrusive, fast and efficient monitoring system long before it became a problem. Such a system is being developed by researchers at the Laser Scanning group at the Fraunhofer Institute for Physical Measurement Techniques (IPM) in Freiburg. The new laser scanner they are working on is smaller than a shoe box and is cheaper, faster and more precise than any others currently in operation. A single high-resolution laser scanner is all that is needed to measure the road surface across a span of four meters. The IPM's Pavement Profile Scanner (PPS) is fixed to a measurement vehicle at a height of three metres. Rotating inside the scanner is an octagonal mirror construction, which steers the laser beam across the road perpendicular to the direction of travel of the vehicle. The signal is reflected from the asphalt back to the scanner, where it hits a special detector chip. The distance between the scanner and the surface of the road is calculated from the time it takes the laser light to travel back and forward - these measurements are accurate to between 0.15 and 0.3 millimetres. Unlike conventional measurement equipment, there is no need for bulky attachments fitted to the vehicle. Instead, only the orientation and position of the vehicle must be known accurately, which is accomplished using the Global Navigation Satellite System (GNSS) and an inertial measurement system. "Measurements are unaffected by external light conditions and can be executed at speeds of up to 100 km/h," explains Dr Alexander Reiterer, Head of the Laser Scanning research group. The PPS has already passed initial field tests. In cooperation with road surveyors from the firm Lehmann & Partner GmbH, the IPM has scanned a total of 15 000 kilometres of highway and other major roads across Germany since last summer, and in the spring the measurement professionals will be combing the runways at Hamburg Airport. It is no coincidence that the laser project is based in Germany. Famed for its autobahn system, Germany's roads - totalling some 626 000 kilometres - are worth 470 billion euros and account for over 60 per cent of the capital assets of many municipalities. But the strain on roads which have seen more than 30 years of service is putting these figures at risk. "The average service life of a road is around 30 years, and the asphalt surfacing rarely lasts more than twelve," explains Dr Dirk Ebersbach, CEO of Lehmann & Partner. In spite of efforts to shift some of the transport burden to rail and water routes, 65 per cent of freight traffic and 82 per cent of passenger traffic is still by road. As reports of ever greater damage become more frequent, the budget for maintaining the road network steadily grows and is set to reach a historic high of 3.5 billion euros in 2016. With such expense predicted, effective means of keeping roads in good condition is of paramount importance, not just in Germany but all over Europe. "In future, we want to go beyond surveying the evenness of a road and be able to detect tiny cracks in a targeted manner, which is a better way of predicting and preventing damage. Up to now, this time-consuming work has been carried out using cameras," says Dr Reiterer.For more information, please visit: http://www.fraunhofer.de
Countries
Germany