|
Weather Applications > Snow and Ice Removal |
|
De-icing, which involves applying sand, salt and other chemicals to break the bond formed between pavement and ice after the ice has formed is a longstanding practice. In the U.S., it dates back to the 1930s, when salt was introduced. The resulting slush is safer for vehicles traveling through it and easier for snowplows to remove. Often, however, de-icing materials are not applied soon enough. Anti-icing techniques began to be tested in the 1990s. Unlike de-icing, anti-icing strategies emphasize prevention and require maintenance operations to anticipate where and when problems will occur. They rely on weather information systems to anticipate ice formation, then spread chemicals—either manually or through automatic systems (usually sprayers) installed in or near the pavement—to prevent water from freezing on roadways in the first place. Commonly, anti-icing chemicals are liquids that prevent ice crystals from bonding to the pavement. They include calcium chloride, sodium chloride, magnesium chloride, and calcium magnesium acetate. Each of these chemical solutions has properties that make it suitable for specific conditions. Trade-Offs: Cost, Effectiveness and Environmental Impacts Generally, traditional materials such as rock salt and salt brine are less expensive, over the short-term, at least. One major trade-off is environmental degradation from run-off of liquids and solids versus the speed and duration of the materials' effectiveness. Air quality can be degraded by overuse of sand, for example, if it causes excessive particulates to be released. Sand can also cause damage to road surfaces and markings. Cost is another concern. To the degree that automated systems enable less material to be used, costs for materials and labor and environmental consequences are kept to a minimum. Reducing the number of applications through judicious timing will cut labor and operational costs as well. The Washington State Department of Transportation (WSDOT) has found, for example, that calcium magnesium acetate is the most environmentally benign but also the weakest anti-icer. It is used primarily for frost control on bridges and overpasses, where concerns about discharges into streams and other groundwater sources are greatest. For roads where freezing conditions are most severe, calcium chloride is the better choice, although it can pose a threat if allowed to disperse into the environment. Often calcium chloride, magnesium chloride, salt brine or other liquid agents are used to pre-wet salt and sand. This helps the mixture stick to the road instead of blowing off to the shoulder when disturbed by vehicle traffic, which reduces the amount of material needed. It also helps the salt work more quickly. The Washington State DOT also uses solid anti-icing chemicals that look like sand and are applied once there are accumulations of snow or ice on roadways. WSDOT is currently testing rock salt and salt brine on sections of Interstate 90 to determine how it performs compared to more expensive chemicals. For more information on WSDOT’s anti-icing program, go to http://www.wsdot.wa.gov/winter/anti.htm. Automated Anti-Icing Systems More than 100 anti-icing systems are currently used in Europe (where they were first developed 25 years ago) on highways, like the German autobahn, as well as on bridges and at airports. In the U.S., they are used in 20 states and three Canadian provinces. Anti-icing systems typically feature sensors embedded in pavement that determine the freezing point of moisture on the roadway and spray discs that dispense anti-icing chemicals over targeted areas. Known as fixed automated spray technology, or FAST, these systems can be activated manually or automatically. There are a number of different automated systems available, and they are especially effective on bridges, which typically freeze sooner than roadways. Non-Intrusive Ice-Detection Laser System Based on technology for detecting ice on aircraft wings, non-intrusive ice-detection laser systems work by firing polarized infrared light from a laser mounted some 20 feet above the roadway. Because ice depolarizes light, the energy signal that is returned indicates whether ice is present, an analysis done by a built-in computer. The computer transmits that data to a server accessible on the Internet, where DOT employees can view an image of an area, obtain readings from the sensor, and decide whether to activate anti-ice measures and issue warnings to motorists about the hazard. The non-intrusive system has several advantages over an embedded system. It covers a far greater area, can be moved easily to another location, and does not require digging up the pavement for installation. Its life span is estimated to be 20 years or more. Alaska’s Department of Transportation tested a non-intrusive laser system in 2004 that scans areas up to 75 feet away for ice formation. Utilizing new anti-icing methods in combination with road weather information systems offers a number of advantages, including the following:
Mobility, productivity, and safety improved substantially when maintenance managers with the Idaho Department of Transportation began an anti-icing program on a 29-mile segment of U.S. Route 12 located in a deep canyon. Sharp curves and shaded areas caused dangerous black ice to form. Rather than spread abrasives, the agency decided to modify trucks used for spraying weed-killers and other chemicals in the summer to dispense liquid magnesium chloride before freezing weather was expected. In the three years following the use of anti-icing chemicals, the amount of abrasives (such as sand) used and the number of crashes each decreased 83%. The pilot program was so successful that anti-icing was expanded to other highways throughout the state. For more information, go to http://ops.fhwa.dot.gov/weather/best_practices/casestudies/007.pdf (140K) An eight-lane, super-elevated bridge over the Mississippi River that was prone to black ice was outfitted with an anti-icing system in 1999. The system’s computer continuously checks environmental sensors to determine the presence of conditions leading to black ice. Once detected the computer activates flashing beacons on approach ramps to the bridge to alert travelers and begins one of 13 different spray programs, depending on conditions. In the first year of operation the number of winter crashes declined 68 percent. For more information, go to http://ops.fhwa.dot.gov/weather/best_practices/casestudies/011.pdf (300K) Salt was corroding parts of the Brooklyn Bridge when the New York City Department of Transportation undertook a project to develop a fixed anti-icing system aimed at eliminating the need for spreading salt. The system is comprised of a chemical storage tank containing liquid potassium acetate, a pump, PVC pipes installed in roadside barriers, check valves, 50 barrier-mounted spray nozzles and a dynamic message sign. When weather forecasts indicate it is necessary to treat the roadway, notice is posted on the dynamic message sign and the system is activated. Each self-cleaning nozzle sprays up to three gallons of potassium acetate for two to three seconds. A closed circuit television camera allows operators to view the system as it works. The system was evaluated over three winters, from 1999 to 2001, and found to improve roadway mobility and safety. For more information, go to http://ops.fhwa.dot.gov/weather/best_practices/CaseStudies/017.pdf (170 K) Operating a snowplow is difficult and dangerous. While hampered by poor visibility from blowing snow and driving on icy roads where traction is limited, snowplow operators must simultaneously monitor their plow activity as well as the application of salt, sand or chemicals. They frequently hit obstacles that are buried in the snow, and motorists crash into the slow-moving plows in the poor visibility and "mini-blizzards" that the plows create as they move along. During the winter of 2003-2004, for example, there were 59 crashes involving snowplows and motor vehicles on Minnesota’s state-maintained highway system. Almost half of the accidents occurred as car drivers attempted to pass the wide plows in poor visibility. Costs for repairing damaged plows or the damage they cause to signs, roadways and guardrails is significant. In 1998, the Minnesota Department of Transportation paid $1.8 million in property damage and $450,000 to repair snowplows in the Twin Cities area alone. Plowing roads, however, is essential for the well-being of local, regional and national economies. Several projects around the country have been undertaken in recent years to wed new technologies, such as global positioning systems, collision warning systems that detect obstacles or other vehicles, magnetic guidance systems and human-machine interface to snowplows. The Highway Maintenance Concept Vehicle What began in 1995 with a collection of 600 ideas for a winter maintenance vehicle concluded seven years later with several prototype vehicles aimed at clearing ice and snow off roadways efficiently, quickly, and safely. The vehicles feature air and pavement sensors, global positioning systems, real-time data communications, an engine power booster, liquid chemical-applying equipment, dry-spreading equipment, back-up sensors, and a pavement friction device. The Concept Vehicle Project was undertaken in 1995 by the DOTs of three states—Iowa, Minnesota and Michigan—the Federal Highway Administration, and an array of private sector partners. Over a period of seven years several prototype vehicles were developed. Each new phase of the project brought changes based on availability of new technology and improvements based on field testing. The vehicle is equipped with:
For a complete description of the project and its findings, see "Final Report: Phase Four Highway Maintenance Concept Vehicle, June 2002" at http://www.ctre.iastate.edu/reports/concept4.pdf (3.6 MB). Project Web site: http://www.ctre.iastate.edu/research/conceptv/index.htm. Intelligent Vehicle Initiative Snowplow Minnesota’s Intelligent Vehicle Initiative Field Operational Test is an effort to integrate technologies and driver displays for safer driving in low visibility conditions such as snowstorms and fog. The technology includes lateral guidance and collision avoidance systems, as well as a heads-up display mounted on the windshield. For lane guidance, the Magnetic Lane Awareness System uses magnetic pavement marking tape instead of the usual lane striping. A magnetic sensor on the vehicle detects the tape when it is within one meter and indicates to the driver the vehicle's position within the lane. The tape is highly reflective, which benefits all drivers using the roadway. A collision warning system uses 360-degree radar around the vehicle to detect and alert the driver to approaching obstacles. Radar detectors are mounted on the front, sides, and rear of the vehicle. On snowplows, the rear radar activates high-intensity strobe lights mounted in the rear to alert drivers moving around the vehicle and to detect and inform the driver of obstacles. A driver interface developed by the University of Minnesota uses a heads-up display mounted on the windshield in place of the rear-view mirror, allowing the driver to see the "computed" road. The display uses differential global positioning data and a digital mapping/geospatial database of the corridor to generate an image of lane boundaries and fixed roadside features such as guardrails, signposts, and other obstacles. In addition, the display incorporates information from the magnetic tape guidance and collision warning systems. Graphic icons in the display depict the position of the vehicle in the lane and any approaching objects. Researchers at the Human Factors Research Laboratory at the university are currently testing a prototype of the heads-up display in the field to determine the best way to communicate warnings and other information. For more information, go to http://www.its.umn.edu/research/ivifieldtest/index.html and http://www.dot.state.mn.us/guidestar/projects/ivihwy19.html Minnesota Specialty Vehicle Initiative: http://www.its.umn.edu/research/applications/winterops.html The Advanced Highway Maintenance and Construction Technology Research Center at the University of California, Davis has been developing systems to enhance the safety and efficiency of snowplows and rotary plows, or snowblowers. The most recent are RoadView and the Advanced Rotary Plow. RoadView technology employs magnets embedded in the pavement along several miles of California roadway on Interstate 80 in the Sierra Nevada, and on Highway 299 near Burney. Magnet sensors, installed behind the front tires of several snowplows operated by the California Department of Transportation (Caltrans) provide data that is displayed on a monitor in the cab of the plow truck. Major components of RoadView include a computer, a human/machine interface with a visual display that shows the snowplow operator where the snowplow is positioned in the lane, and two forward radar sensors that can "see" approximately 100 yards ahead of the plow and warn the operator of trees, vehicles or other obstacles that may be buried under snow or invisible due to blowing snow and road conditions. Information is collected from the magnets in the pavement and is relayed to the computer that interprets that data and provides an image on a visual display mounted on the windshield. For more information on RoadView, go to http://www.ahmct.ucdavis.edu/roadview/r_mn.htm Rotary snowplows, or snowblowers, are a key component of the snow removal strategy in mountainous areas. To effectively remove piles of snow that accumulate after the snowplow fleet passes, blowers must drive along the edge of the road often using guardrails as a guide. Unfortunately, this frequently damages the guardrails, which are expensive to repair or replace. Stalled or abandoned vehicles on the edge of the roadway, and the presence of natural objects, such as large rocks and debris on steep mountainous areas, also present hazards for snowblowers. With these conditions in mind, the Advanced Highway Maintenance and Construction Technology Research Center at the University of California, Davis installed a magnetic guidance system that helps the blower stay a specified distance from the guardrail. The 28-foot-long prototype snowblower is also equipped with a collision warning system to detect objects buried in the snow. The center is also automating many of the driving functions of the snowblower, including steering and possibly automated throttle and brake. For more information, see RoadView Winter Research, AHMCT Research Center, April 2000, at http://www.ahmct.ucdavis.edu 1. Robert A. Ferlis, Shahed Rowshan, and Cathy Frye, "Safe Plowing - Applying Intelligent Vehicle Technology," Public Roads, January/February 2001 2. Deborah Vocke, "Learning to Beat Snow and Ice," Public Roads, January/February 2001 3. "Driver-Assistive Systems for Snowplows," ITS Institute, University of Minnesota, 2003 4. "Better Winter Maintenance Management," Better Roads, October 2004 5. "Pixel Watching: New Technology Benefits both the DOT and the Motorist," Roads & Bridges, December 2004 6. "Automated Anti-Icing Systems Show Potential as Solution to Slippery Streets,” Research & Technology Transporter, November 2004 7. "2003 WSDOT Anti Ice/Snow and Ice Control Update," Washington State Department of Transportation. 8. "Road Temperatures And Weather Conditions Combined On The Internet Just In Time For Winter," rWeather Newsletter, Volume 4 Winter 2000/2001 Last Update: April 6, 2005 |
|