The progressive growth of hidden cracks within railroad tracks, known as "rail cancer," is a major safety hazard in the railroad industry. Crosswise cracks that begin with tiny flaws inside the steel rails can grow into surface cracks and eventually cause the rails to break. In the effort to prevent derailments, service cars equipped with special sensors travel the nation's railroads, seeking out signs of rail cancer and other defects. But because the sensors require direct contact with the rails, the cars have to creep along at speeds averaging less than 15 miles per hour, forcing commercial train traffic in the area to shut down.

Finding a more efficient, cost-effective method of track maintenance and inspection is a high priority for the railroad industry, according to Jim Lundgren, head of the American Association of Railroads' (AAR) Technology Scanning Program for identifying and addressing critical areas of railroad-related research. "We need the ability to do more frequent and thorough inspections that do not interfere with revenue-generating traffic," he says. Now an MIT team led by civil and environmental engineering professor Shi-Chang Wooh is investigating ways of detecting potentially lethal cracks at high speeds while the nation's trains are running.