Nearly forty percent of all bus crashes are side impacts with people or cars. While not all can be prevented, the difficulty bus drivers have in seeing what’s next to them has prompted efforts to develop side-mounted sensors and driver-warning systems. One problem with these devices is false alarms-warning drivers of pedestrians safely strolling down the sidewalk, for instance. A group at Carnegie Mellon University’s Robotics Institute has created a laser-and-camera system that would sense the presence of a curb, alerting the driver only to obstacles between the bus and the curb. “If you know where the curb is, you can cut down on unnecessary alarms,” says research associate Christoph Mertz. The device, funded by the Federal Transit Administration, shoots out low-power laser beams and determines the distance to an object in a beam’s path by triangulating the beam with the line of sight of a camera mounted nearby. The system worked well on a test car this spring; field tests on a Pittsburgh bus are scheduled for July.