CM 3000™ Development Background

 

All state DOT’s are required by FHWA to acquire and update their overhead clearances on their major routes. In addition, many states require that these measurements be recorded along each painted lane line. Although measurements are usually made when a bridge or sign or other structure is built or installed, paving operations below the structure can significantly affect the actual clearances, therefore, they need to be periodically updated. Traditionally, these measurements have been made manually with telescoping rods and more recently, with hand-held ranging lasers. The major drawback to this approach is, of course, safety of the personnel who must be out in the actual roadway to accomplish this. Therefore, typical overhead clearance measurement operations would be completed at nighttime and would require not only lane closures, but often needed support from local law enforcement authorities to help handle the traffic diversions.

In 1994, BDI proposed an alternate option to the Colorado Department of Transportation (CDOT) that included the development and delivery of a laser-based system that could be mounted on an inspection van and driven under the structure and the data stored in a digital format. At that time, the technology only allowed relatively slow sample rates, so the van was limited to traveling below the bridge at approximately 5mph. Even though this was slow, it was a huge improvement over the manual system, especially since the personnel were no longer required to be out on the roadway at night. This system also drastically cut down on field support since now just a driver for the van and a computer operator were needed, along with one “cushion” truck to follow and basically provide a moving roadblock. CDOT proceeded to use this system for several years for updating clearance measurements, primarily in the Denver metropolitan area. Again, due to the slow speeds required, this operation was usually completed at night when traffic counts were lower.

Over the next ten years, BDI worked on the development of this system to include features such as ensuring that the measurements are made vertical and software upgrades that allow the data to be stored in a format that most DOT Bridge Management Systems can readily accept. However, the most dramatic improvement involved the integration of an on-board PC along with a much faster laser system that effectively allows accurate measurements to be recorded as the vehicle passes below the structures at speeds up to 75mph! This improvement alone has now allowed the measurement operation to be completed without a cushion truck or any other traffic control whatsoever, plus the operation can now be completed in daylight hours.

Implementation of the system is very straightforward and adaptable from vehicle to vehicle, therefore it can be easily implemented by DOT personnel or their designated contractors.