A winter storm descends on the region. Schools close. Snow drifts across roadways, creating low visibility. But one DOT employee isn’t worried about potentially treacherous driving conditions.
On his computer screen, he has real-time images of problem bridge decks, curves in roads and other icing-susceptible areas, images that show precisely where ice, snow and water are accumulating. So he can dispatch snowplows and sand trucks precisely where they’re needed.
No, this is not a scenario from the future. It’s what is possible today with a unique, non-intrusive laser system (Circle 915) based on technology previously used to detect icing on aircraft wings.
“The (non-intrusive laser system) was a natural extension of our aircraft ice detection technology,” according to Paul Schmokel, engineering manager, Goodrich Sensor Systems. “If we could improve safety and streamline operations for airlines, it only made sense to provide the same advantages to those managing road travel.”

Laser show

Unlike current road weather information systems that are embedded in the roadway surface, the non-intrusive laser system is remotely mounted above the roadway. An active, eye-safe infrared laser scans areas up to 75 ft away.
The laser fires 60,000 pulses of polarized infrared light in 15 seconds. Based on the principle that ice depolarizes light, a built-in computer analyzes the returned energy signal. Within minutes, it can transmit that data to a server accessible on the Internet, where DOT employees can access an image of the area. The image covers up to 1,800 sq ft of the roadway, with colors delineating exactly where ice, water and snow are on the road surface.
With more comprehensive and accurate information, DOT employees can be more confident of their decisions regarding road condition monitoring and management. In addition, the non-intrusive laser system can be used to activate ice alert warnings and reduced speed limits. On bridge decks, it can provide a trigger for automatic, bridge-mounted spray systems. It can even track the quality of ice and snow removal services. Since the system is portable, crews also can take the system with them to monitor road conditions in problem areas.
The Alaska DOT ran a test of the system in the spring of 2004. According to Keith Knorr, DOT highway maintenance manager in Skagway, “With this system, you can see right where your troubled areas are. You can tell what road conditions are like before you send trucks out. You can be smarter about how many trucks and how much sand you need.”
Mounted above the roadway, the non-intrusive laser system components include a sensor module that contains the optics and camera, and an electronic module that controls the laser, retrieves and stores images and provides input/output communications.

Always working

Because the non-intrusive laser system is mounted above the roadway, and not imbedded in the highway, there’s no need to dig up the road to install it. It also requires minimal periodic maintenance. In fact, it’s estimated that the system has a life expectancy of 20 years or more. If replacement or upgrading is ever needed, it can be accomplished without affecting traffic or putting highway workers in harm’s way.
With 60,000 sensing points per scan, the system can provide more complete and accurate data than other road condition indicator technology. In every 200 x 300 pixel image generated by the system, every pixel is analyzed for the presence of ice, snow and water. Reviewing these images, DOT employees can make more informed decisions based on objective data.
Since the system provides a wide area of coverage, it offers cost advantages. One unit can cover more ground than several embedded sensors and provide more data. What’s more, if the road is redesigned or closed, the system isn’t obsolete—it can be moved to another location.
With more accurate information on road conditions, it’s easier to make decisions about chemical application. For instance, if the system shows that chemicals applied three hours ago are still effective, employees can delay trucks from laying down more chemicals until needed. This can save the county or state unnecessary expenditures.
The non-intrusive laser system is flexible enough for users to program measurement frequency and sensitivity to their specific needs. The system can be programmed to take images at user-defined intervals, on command, or as an alert when road conditions deteriorate. For instance, on a clear day with no snowfall, the system can alert users of the development of black ice caused by snow blowing across the road. Images can be stored for later analysis or discarded.
Used as a stand-alone system, or integrated into an existing system, the non-intrusive laser device can be operated remotely or locally, manually or in automated mode. And the system architecture allows for future expansion and enhancements.
Alaska DOT’s Knorr added, “Our state is looking for ways to use new technology to be more efficient in roadway maintenance. This system is an example of new technology that could be very helpful.”

Alaska approval

In April of 2004, the Alaska DOT tested the non-intrusive laser system in two sites near Skagway, where roadway elevation goes from sea level to 4,000 ft. In both cases, the system was raised 21 ft above the road surface.
After images of clean road surfaces were taken, snow was blown onto the road to a thickness of approximately 0.25 in. The snow was composed of large crystals to reproduce the effect caused by partial melt and re-freezing of snow.
Snow, ice and water were correctly identified by the system and confirmed visually by inspection of the road surface.