Publication Number: FHWA-SA-98-023
Date: June 1998

Software Helps Keep Snow in Its Place

The Wyoming Department of Transportation (DOT) is no stranger to snow fences. For nearly 30 years, the highway agency has been using snow fences to prevent blowing and drifting snow from covering roads and impairing motorists' ability to see other vehicles. Despite all this experience, it's still difficult and time-consuming for DOT staff to determine exactly which sections of road will be affected by blowing and drifting snow.

To make this process easier, Wyoming DOT is testing new software tools that enable its roadway design staff to quickly determine if drifting snow will be a problem and where they should either place snow fences or change the topography of the project site to keep roads clear.

Wyoming's software tools are based on research conducted by Ron Tabler, including work he did under the Strategic Highway Research Program (SHRP). The research resulted in precise guidelines for placing snow fences for maximum benefit.*

The SHRP guidelines involve more than just a few simple calculations. First, you need to collect information on average snowfall, winter temperatures, wind speed and direction, and the project site's topography. You then work through dozens of formulas to arrive at an estimate of how much snow will accumulate on a roadway, the dimensions and location of the snow drifts, and where snow fences will be needed to control the drifts.

Tabler recognized that the guidelines were perfect for computerization. "The procedures in the report were formatted to lend themselves to programming," he says.

Wyoming DOT anticipates that the software will handle virtually all the steps in the SHRP guidelines, from assembling the needed weather information to determining the location of a snow fence. The system has two components. The first is a set of computerized maps of Wyoming that Tabler developed for the highway agency. The maps contain information on prevailing winds and average snow accumulations for the entire State.

The second component is a customized snow drift module that works with commercial roadway design software. The snow drift module, which uses the formulas in the SHRP guidelines, determines where snow drifts will form based on prevailing weather conditions and the project site's topography. The module is now being reviewed by Wyoming DOT. The software module is expected to be available late this year from GEOPAK Corp. as part of its roadway design software package.

Here's how it works. First, you consult the computerized map to obtain the wind and snow conditions at the project site. You then enter information on the topography of the project site into the roadway design software. Next, you enter the weather information into the snow drift module.

The module determines if the site's weather conditions and topography will cause a snow drift to form on the road and plots the shape and location of the drift (Figure 1). If you add a snow fence upwind of the road, the module plots where the drift will form, showing at a glance that the fence will protect the roadway (Figure 2). You can also change the topography of the road to prevent a drift from forming.

The snow drift module makes it easy to determine where to place snow fences, but it would be a chore to use without the computerized maps, says Paul Bercich of Wyoming DOT. "The big thing for us is that snow precipitation and wind direction vary so much in different parts of the State. Now, thanks to Dr. Tabler's study, that information is right at our fingertips."

Snow drifts are also a big problem in New York State. There, the State highway agency has contracted with the State University of New York-Buffalo and Brookhaven National Laboratory to develop a similar software program. When completed, the program will allow roadway design engineers and maintenance engineers to enter readily available or easily obtained information on weather and topography and then determine the best approach to snow drift control at the site-redesigning the highway cross-section, installing snow fences, or planting trees or other vegetation.

"The program will allow users to plug in the numbers, get the best answer, then do 'what ifs' to see what other options there are," says Joe Doherty of New York State DOT. He says the ability to look at different solutions will make the software particularly useful for States like New York, where the lack of public land and the relatively high population density can make it hard to find suitable locations for snow fences.

New York State DOT plans to test the software over the next two winters and will eventually make the program available to other State and local governments.

For more information on the Wyoming DOT project, contact Paul Bercich at Wyoming DOT (phone: 307-777-4135; fax: 307-777-3852; email: pberci@missc.state.wy.us).

For more information on the New York State DOT project, contact Joe Doherty at New York State DOT (phone: 518-485-7271; fax: 518-457-4203; email: jdoherty@gw.dot.state.ny.us).

For more information on the GEOPAK software module, contact Derricke Gray at GEOPAK (phone: 850-942-4023; fax: 850-656-7944; email: derricke_gray@geopak.com; Web: www.geopak.com).

For more information on snow fences, contact Salim Nassif at FHWA (phone: 202-366-1557; fax: 202-366-9981; email: salim.nassif@fhwa.dot.gov).

* Design Guidelines for the Control of Blowing and Drifting Snow, Washington, D.C. National Research Council, 1994 (Publication No.SHRP-H-381). To order, call 202-334-3214 (fax: 202-334-2519).

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