DEVELOPMENT AND USE OF A LASER-BASED ROADWAY CLEARANCE MEASUREMENT SYSTEM

The Federal Highway Administration (FHWA) requires each state to maintain an accurate record of roadway clearances on all routes. Obtaining the vertical clearances can be particularly difficult on highways carrying high traffic volumes such as Interstate 25, a major North-South route through the heart of Denver. In the past, the Colorado Department of Transportation (CDOT), like other agencies, measured these clearances manually with telescoping rods. In the most congested corridors, this method required lane and/or road closures. It also required personnel to be physically out on the roadway subjecting them to hazards from unaware drivers. In the metropolitan areas, the operation was usually performed at night when traffic volumes were lower, raising even more safety concerns because of the difficulty for vehicle drivers to see the personnel on, or near, the roadway in the dark. Through an agreement with Bridge Diagnostics, Inc. (BDI) of Boulder, Colorado, a laser-based device and associated software were developed to measure vertical clearances while in motion. By combining laser and ultrasonic technology, the system measures and records the clearances, eliminates most of the safety concerns of personnel being out on the roadway, provides more accurate measurements, and requires significantly fewer resources to collect the clearance data. This paper discusses the development of the system, the accuracy of the results, some of the unanticipated problems that were encountered, and the procedures developed by CDOT to record clearances along their most heavily traveled routes.