Troy Gilbertson has been with the North Dakota Department of Transportation for 15 years and currently serves as a highway maintenance coordinator for a five-county district in the southeast corner of the state.
He and his crews maintain 1,800 miles of road, including sections of two major interstates, I-29 and I-94. In that part of the country, the inevitability of snow and icy conditions during late fall and early winter raise concerns about difficult travel conditions and increased accidents.
According to Gilberston, situations begin in the fall when frosting begins. For years, his department typically responded after a weather event.
“The automated bridge anti-icing technology simply didn’t exist to be more proactive,” he said. “Now with forecasting technology, pavement sensors and automated bridge spraying equipment, we are able to get out there ahead of time and do the pretreating, which we believe significantly reduces accidents.
“With the equipment and technology available now, we can do a much better job of predicting and reacting to frost and snow events.”
Two years ago, a federal grant enabled Gilbertson’s district to install an automated bridge spraying system that includes a road weather information system (RWIS) that now allows Gilbertson to know when frost occurs (when the pavement temperature and the dew point get within about 1.8°F). It also allows him to do pretreating with anti-icing agents versus deicing after the fact.
Sensing snow
The anti-icing system and RWIS are located on I-29 between Fargo and Grand Forks, N.D., at mile-point 114 on two bridge structures that are each 300 ft long. Gilbertson said the site was selected because it has a high crash history.
Motorists along that stretch of interstate are typically cruising along when they enter a series of curves and a hill leading into the bridges, which can become slick when conditions are right. Last year, from Dec. 24 through the middle of April, Gilbertson recorded more than 190 events where conditions were right for the system to activate, and he said it was highly accurate, which “is outstanding.”
The RWIS and anti-icing system in place at the North Dakota bridge site contains an active sensor in the pavement that collects a sample of a chemical or liquid that is on the roadway. The active sensor uses a Peltier cell to cool and warm any moisture or liquid on the pavement to determine its freezing point. Using the data from the active sensors, the system will automatically spray anti-icing chemicals in advance of freezing conditions.
There are 10 spray nozzles on the decks of the bridges and two on the approaches in each direction. North Dakota uses CF-7, a potassium acetate-based product. Gilbertson said that CF-7 is $2.86 a gal when purchased in bulk quantities. The bulk chemical is stored at an off-site location and delivered to the site by a nurse tank in the back of a truck.
The sensors connect to a remote processing unit (RPU) located in a shed-like structure adjacent to the roadway that transmits the information to a server located at the state headquarters office in Bismarck. Gilbertson views the information on his computer, approximately 50 miles from the site, using the state’s intranet. The server collects data from the remote units and forwards the data to a user display. Gilbertson can access the data via software from his computer workstation at the office or from other intranet locations outside of his office. The shed also houses a 500-gal tank of liquid anti-icing chemicals, a pump, system controller, etc.
The RWIS sensors embedded in the pavement measure temperature, moisture, form of moisture (snow or ice) and amount of deicing chemical present. Atmospheric sensors determine air temperature, relative humidity, wind speed and direction, precipitation and visibility.
Controlled environment
Gilbertson said in spite of all the sophistication of the system, it does provide a lot of flexibility.
“We can program when we want the system to ‘fire,’” he said, “and you can program in a high and a low temperature so that automatic activation won’t occur beyond those parameters. You can also set parameters for wind speed so that you are not spraying chemicals on windy days that are conducive to blowing and drifting snow across the bridges.”
Gilbertson has his system programmed so that it won’t spray if wind speeds exceed 20 mph.
He added that it can be programmed when you want it to refire based on the freeze-point condition or a frost condition as well, and it can be manually overridden to spray at any time right from the desktop at his home or office. Additionally, he can control how many gallons of chemicals have been sprayed, how much each nozzle sprays, etc., right from his computer.
Gilbertson said that the system also has a camera installed which takes a shot of the bridge about every 15 minutes so that he can monitor its operation from his computer as well. When the system fires, it also is programmed to call his office phone and alert him that something is going on so he can call maintenance. The web-based system also allows remote maintenance sections to view roadway conditions from their home or office.
“This is a tremendous benefit,” he said. “It might be sunny and dry at our office but snowing at the bridge. The system serves as an alert as well so we can get highway maintenance crews out there before conditions get too bad on other sections of the interstate in the area of the bridge.”
The system can be viewed at www.state.nd.us/dot in the road and travel information section, which includes summaries of the weather and pavement conditions at the bridge that the public can access.
Gilbertson said that his agency is planning a joint project in the summer of 2005 with the Minnesota DOT to put in a similar automated anti-icing system on two bridges that span 1,300 ft over the Red River where I-94 crosses between North Dakota and Minnesota.
