In many situations when monitoring a civil engineering structure such as a bridge, non-contact sensors are desired due to the difficulty to access the site or establish a reference point. Newport Sensors, Inc. has developed a low-cost, non-contact, real-time displacement monitoring system composed of a digital camcorder and a notebook computer. The captured images are streamed into the computer, and proprietary image-processing software computes the structural displacement in real time. A field experiment was performed on a bridge. Response displacement of the bridge to a vehicle running at different speeds were measured at the center of the span in the vertical direction by three different sensors: a conventional contact-type displacement transducer, a high-cost non-contact laser vibrometer, and the low-cost vision-based system. Excellent agreement was observed among the displacements measured by the three types of the sensors.