Five years after a bridge collapse in Minneapolis, wireless sensor technology to prevent such tragedies has become \"affordable and practical,\" engineers say. On August 1, 2007, Minneapolis\' I-35W Bridge collapsed, sending more than 100 cars into the Mississippi River, killing 13 and injuring145. Engineers at the University of Maryland say a new generation of wireless sensors could prevent another tragedy by monitoring the nearly 150,000 U.S. highway bridges -- about one in four -- listed by the federal government as either \"structurally deficient\" or \"obsolete.\" \"We no longer need to roll the dice when it comes to the structural integrity of the nation\'s highway bridges,\" research engineer Mehdi Kalantari said. \"Technical advances in wireless sensors make real-time monitoring both affordable and practical.\" Researchers have developed a system of tiny, long-lasting, energy-efficient low-maintenance wireless sensors and software that analyzes real-time data collected, a university release reported Tuesday. Many bridges, including the replacement span in Minneapolis, now used use wired networks of sensors to detect problems, but these wired systems are generally too expensive to retrofit all the old bridges that need them, Kalantari said. A few dozen tiny wireless sensors, strategically placed on small to medium-sized bridges, could measure prime factors such as strain, vibration, deformation, pressure, tilt, inclination, displacement, crack activity, humidity and temperature at less cost than current technology, he said.