Let it snow, let it snow, let it snow: 11 ways to maintain winter roads
The emphasis in winter road maintenance is shifting as new tools become available in the war against Mother Nature. High-tech strategies, like field detection systems, anti-icing techniques and thermal maps, are replacing reactionary battle plans.
In January, after being stung by a blizzard that featured wind chills of 90 degrees below zero, Minnesota authorities ordered snowplows off the roads and threatened to arrest any driver makings a non-emergency trip, according to the Associated Press.
The storm dumped more than a foot of snow in parts of Minnesota, Nebraska, Wisconsin and the Dakotas.In the South, hundreds of traffic mishaps occurred around the metro Atlanta area as sleet turned some bridges and overpasses into black-ice nightmares. DeKalb County, Ga., police reported 150 accidents within a 40-minute period.
All across the country, highway officials battled the white stuff as snow-plows and salt trucks struggled to keep roads open.
But this year, the weapons arsenal has increased, thanks in part to advances in technology and a five-year program recently conducted by the Federal Highway Administration (FHWA).
Previously, winter road strategies were based on reactive battle plans as highway departments simply waged war against Mother Nature after she had raged her icy, cold fury.
But the emphasis has shifted toward preventive measures as anti-icing techniques, field detection systems, thermal mapping and pavement studies have emerged.
Anti-icing vs. de-icing. The $150 million, five-year program, begun in 1987, included an anti-icing initiative, which was carried out in nine states during a two-year period.
The program’s results were favorable and proved that anti-icing techniques could effectively fight winter road complications by improving traction and safety during storms.
The project, Test and Evaluation Project 28, was conducted during the winters 1993-1994 and 1994-1995 to examine the strategies that hold the greatest potential for anti-icing success over a range of topographical, climatological and traffic conditions.
The test results showed that chemical agents can be used much more effectively to prevent the bonding of snow or ice to pavement – anti-icing – than to destroy the bond once it has already been formed – de-icing.
In some cases, anti-icing required fewer chemicals for the same level of maintenance than de-icing, procedures, according to Public Roads’ winter issue. “In others,” the article notes, “the same amount of chemical used produced an increased level of maintenance as compared with de-icing control operations. Anti-icing also reduced the need for abrasives.”
Prewetted salt vs. dry salt. Salt is normally spread on snow- or ice-covered roads to debond the snow from the pavement as it melts. However, salt is an environmentally corrosive agent that must be reapplied frequently as it is plowed aside.
“Because a chemical in the de-icing mode must in essence play catch-up with the precipitation already on the roads, heavy snowfalls may prove too much for the chemical’s best efforts and can result in a slippery packing of bonded snow on the pavement’s surface,” Public Roads states.
Prewetted salt versus traditional dry salt application processes can help a little, because:
* less material is needed for each application, so less material enters the environment;
* more material stays on the road surface – especially true for black-ice conditions, damp roadways or slippery conditions;
* material distribution is improved;
* the spreading width of material can be controlled more effectively since prewetted salt bounces less than dry salt;
* spreading routes per truck are increased, resulting in fuel savings and less down time spent heading back to reload;
* a potential for reduction in labor and equipment resources exists; and
* the effect is immediate and the temperature range of effectiveness is increased.
Because salt requires moisture before it can dissolve and become more effective, below-freezing temperatures with little unfrozen moisture present complications. Prewetted salt receives the necessary moisture from an external source.
Additionally, with temperatures lower than 19 degrees F, the melting process for salt takes longer. Prewetted salt forms a solution from the outset.
Determining how much moisture is necessary, which liquid water, NaCl brine, magnesium chloride, calcium magnesium acetate, potassium acetate or calcium chloride should be used and what particle size of salt to use, depends on conditions at the site.
Ice melters. Calcium magnesium acetate (CMA) is a biodegradable chemical de-icer first identified by the FHWA as an environmentally sound, low-corrosive alternative to rock salt.
Developed primarily for surfaces and structures where concrete protection is crucial for safety – such as parking garages and bridges – two granular ice melter products manufactured by Vigoro Consumer and Professional Products Group, Winter Haven, Fla., use CMA at effective concentration levels.
The chloride-based ice melter is blended with a 20 percent concentration of CMA, providing effective ice melting capability below 0 [degree] F and reducing corrosion by as much as 70 percent to 80 percent over rock salt.
The second ice melter formulation contains 100 percent CMA, virtually eliminating corrosion of concrete or steel surfaces while providing extended ice melting effectiveness.
It is less corrosive than tap water and does not harm vegetation or drinking water supplies.
High-quality ice melters can help clear roadways quickly, but several things must be considered, including:
* selection of a product that will best prevent re-freezing;
* avoidance of ice melters such as calcium chloride and rock salt that can damage the environment through runoff and plowing; and
* the shape of the de-icers. De-icers with an irregular, granular shape will provide better gripping action.
Field detection systems
Roadway Weather Information System (RWIS). Highway officials, like those at the Nevada Department of Transportation, rely on information from the Roadway Weather Information System (RWIS), located at Turner-Fairbank Highway Research Center in McLean, Va., to determine the appropriate time in which to begin anti-icing operations.
The RWIS reports dew point, humidity, air temperature and wind velocity and direction and makes use of pavement sensors that monitor pavement temperatures as well as the amount of anti-icing chemicals currently present on the pavement.
The information is recorded and fed into a central database, where various modeling techniques help predict the start of ice formation on pavements and offer advice as to when to apply the anti-icing chemicals.
Friction measurements – pavement friction to automobiles measured by commercially available friction instruments installed in a vehicle – help to determine whether and when more chemical needs to be applied.
CASPER. The Indiana Department of Transportation (INDOT) is responsible for snow and ice control on 29,000 lane-miles of roadway. INDOT’s goals include providing safe driving surfaces for the public, designing efficient snow routes that make cost-effective use of maintenance equipment and personnel and using de-icing materials efficiently.
Meeting these goals requires nearly 1,500 trained personnel and about 1,200 maintenance vehicles, as well as $9 million spent to support these operations. In addition, nearly $22 million is spent annually on winter road-related activities.
A new computer-aided system is helping the department find effective routes, improve operations and reduce costs. Developed by INDOT maintenance engineers and researchers at Purdue University in West Lafayette, Ind., the Computer Aided System for Planning Efficient Routes (CASPER) is being implemented throughout the state. The support system consists of three main components:
* a Global Information Systems database containing detailed information about physical aspects of the transportation network;
* a set of models for optimizing route design; and
* a user interface that allows INDOT to interact with the data and models efficiently.
So far, CASPER has been used in three INDOT districts, redesigning snow routes for winter maintenance vehicles and resulting in significant savings. The system has reduced the number of snow routes by 17 in these districts, thus eliminating the need to purchase 17 new trucks.
The Fort Wayne District alone eliminated the need for eight new trucks and saved about $520,000.
The resulting savings is more than $1.1 million, with potential annual savings of up to $139,400 on operational costs.
Detection sensors. In addition to systems designed to predict winter weather and when to begin road care, tools such as pickup-mounted sensors, like infrared pavement surface temperature mechanisms, are available, monitor road or runway temperatures, and are used to determine salt application rates for various thicknesses of snow or ice pack to be removed from the road. These sensors can perform while the vehicle is traveling at highway speeds.
When both moisture and temperatures below 32 degrees F are detected by the monitors, it is time to de-ice.
The system features a road surface temperature sensor, mounting equipment, a shield to protect the sensor and a dash-mounted digital display backlighted for night use, mounted in plain view of the operator. By connecting the system to the vehicles’ 12-volt electrical system – like that in an ignition switched line – operation is simple and automatic.
One new preventive icing system sprays bridge decks with a chemical de-icer before freezing moisture can bond with the road. The system uses electronic sensors, nozzles installed below the surface of the deck and just-in-time activation to reduce the amount of chemical de-icer needed.
Ice Predicting Systems. Management of winter roads is a challenging task. Safety, the environment and cost must be taken into account simultaneously. When optimizing winter maintenance, it is vital that decisions are based on correct and up-to-date information. Reliable meteorological information is required both in advance and in real time to make accurate decisions on how much chemical is required and when and where it should be applied.
An ice predicting system has been under development by Vaisala, Woburn, Mass., for several years that is based on three main elements:
* a unique pavement condition sensor that detects the temperature and physical state of the road when embedded with its surface flush with the road;
* a suite of software that not only collects and displays data related to the actual conditions at the roadside but also predicts the temperature and the state of the road surface for a 24-hour period; and
* a thermal map of the road network that identifies areas within the network that are systematically warmer or colder than average and will accordingly freeze later or earlier than the rest.
The Icecast system incorporates a unique numerical model of the heat balance at the road surface.
Meteorological data, including forecasts of air temperature and cloud cover, are used as inputs to the model, along with the data gathered by the computer itself from the sensors at and in the road.
From these data the computer calculates the temperature of the road surface at fixed intervals of time for a defined future period, normally 24 hours.
This forecast is presented to the user as a graph of road surface temperature against time from which it is easy to determine whether and when the surface will freeze.
The model also predicts whether the road surface will be wet or dry when freezing conditions occur, giving a complete picture of the expected state of the road for the forecast period.
Model predictions help determine:
* whether the pavement temperature will fall below freezing;
* at what time the temperature will actually fall below freezing;
* whether the surface will be wet when the temperature falls below zero; and
* how long the surface temperature will remain below zero.
In addition, a narrative forecast, provided by a local weather service, can give an overview of major developments such as the occurance or clearance of hazardous conditions (snow or fog) and the general developments expected over a specified period.
Thermal mapping. Working similarly to detection sensors, an infrared thermometer can be mounted in the floor of a vehicle to measure road surface temperature at night.
The results clearly demonstrate that each road has a set of thermal fingerprints – certain stretches of road that are consistently colder than other stretches, which are displayed using multi-colored temperature graphs.
These systematic temperature variations are due to the effects of topography, road construction, traffic density, exposure and altitude.
The scale of the variations on any given night is determined by the actual weather conditions.
Multi-colored temperature graphs and color-coded temperature maps, called “thermal maps,” are evaluated in a detailed technical report.
The map clearly shows the location of areas within the network that are most susceptible to freezing and how these areas relate to others within the road network.
Once these locations have been identified, it is easier to predict how the streets will react on a night when the temperature goes below freezing.
Armed with thermal mapping information, winter maintenance engineers can monitor certain areas for signs of freezing and treat those areas first, reducing the time that ice or frost stays on the road.
The information also helps in pre-treatment of roads, preventing the formation of ice or frost on freezing nights.
And, if the installation of road sensors is desired at some later date, the thermal map can be used to help strategically locate those sensors to give the best representation of the roads in question.
Using the thermal map may actually reduce the total number of sensors required for full coverage; it also allows for the interpolation of thermal information between sensor sites.
This information actually helps reduce the amount of de-icing chemical used while providing as safe or safer road conditions for the local motorist.
International Scanning Program. ISTEA recently authorized an international scanning program to help learn about advanced technologies developed abroad that might have application in the United States.
So, in 1994, the FHWA, the American Association of State Highway and Transportation Officials (AASHTO) and the Transportation Research Board (TRB) organized a trip to Europe to learn about international winter maintenance strategies.
The technologies reviewed during the trip include:
* plow attachments that prevent snow spoils from blocking driveways;
* a highly instrumental snow plow with front, side and underbody plows;
* geothermal water sprays for melting snow on roads;
* airfoils to keep snow off the back of the spreader, increasing visibility to vehicles approaching from the rear;
* snow gutters. Water continuously flows through the gutter – as citizens clear driveways and paths in urban areas, they shovel the snow into the gutter where it is carried away; and
* automated snow and ice control fixed-spray systems on bridges or steep roadways. These systems work well in frosting conditions – sensors at the site automatically energize the systems for application.
While Mother Nature will always be a strong contender in the battle, taking a proactive approach and staying abreast of the array of new technologies and tools that are available in the 20th century is one way to stay in the fight.
Of course, another option is to just stay home.