California Department of Transportation

DRI Laser Detector

What is it ?

Caltrans Division of Research and Innovation (DRI) and UC Davis have developed a new type of out-of-pavement traffic detector based on a patented use of laser technology. This detector has ultra-high resolution, sampling so fast that it simply cannot miss any vehicle passing underneath it. It not only determines traditional "speed, volume, and occupancy" data with hereto unseen accuracy, but has the ultra-high precision to not just "detect" vehicles, but to quasi-uniquely "ID" each one, allowing travel time and origin/destination to be determined across the instrumented roadway sections.

DRI Laser Detector
DRI Laser Detector


According to the Caltrans Performance Monitoring System, PeMS, a very high percentage of Caltrans' existing deployed loop detectors are not generating usable data. Both the Division of Maintenance and Division of Traffic Operations have recurrently called for the development of out-of-pavement detectors as a replacement, being as there are few resources available for the time consuming and hazardous job of in-roadway loop maintenance.

Most existing alternates to loop detectors have significant limitations. Radar detectors, although relatively easy to place on the side of the road, are difficult to calibrate, and have proven to not be very accurate. Acoustic and video image processing system have been evaluated but are also lacking in 24/7 accuracy. Laser based scanning Lidar systems have been tried but are too mechanically and electronically sensitive to be widely field deployed without excessive recurrent maintenance requirements. Electronic tag based readers generate travel time data in some urban areas, but the readers are few and far between, don't generate flow rate data, and raise privacy concerns.

A better detector is needed. Hence, UCD and DRI developed and patented a new breed of detector. This detector samples at 10,000 times a second, fast enough to generate much more accurate speed, volume, and occupancy data than any other traffic detector.

Increasingly, travelers are asking for travel time--the time it takes them to travel from point A to B. This requires re-recognizing the vehicle at point B that has passed point A, which requires re-detection of one or more identifying vehicle characteristics. This detector determines both the vehicle length and bumper curvature to within a few centimeters, accurate enough to re-recognize most vehicles using the same re-correlation techniques previously deployed by DRI.

Travelers not only want to know the current travel time to their destination before they depart, but want to know how travel time will vary in the immediate future when they actually get to the roadway. Future predictions of travel time require validated traffic models, and accurate origin/destination (O/D) data is an essential component for any predictive traffic model to work. This laser detector not only determines the actual travel time, but makes possible the accurate determination of the future anticipated travel time by feeding O/D data to these "look ahead" traffic models. Unlike ETC tag readers, cell phone trackers, or license plate readers, this detector does not and cannot acquire any personal individual information on the driver or vehicle; and unlike other methods, it works for 100% of the actual vehicle fleet from the get-go.

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Joe Palen