1. A method for monitoring the condition of a bridge comprising the steps of: stably positioning a video camera at a selected location and having an unobstructed view of a selected portion of the bridge structure; collecting a video file of said structure over a selected total time interval; using a data processing system to analyze the video and calculate a physical parameter related to movement of said selected portion of said bridge structure as a function of time, wherein said data processing system is controlled through a graphical user interface (GUI) having at least the following features: a display of a single video frame corresponding to a selected time within said total time interval; a movable area selector superimposed on said video frame to indicate the selection of an area of said structure for analysis; and, a display of displacement versus time for said selected area over said total time interval.