U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

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Federal Highway Administration Research and Technology
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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-04-136
Date: December 2005

Enhanced Night Visibility, Volume V: Phase II—Study 3: Visual Performance During Nighttime Driving in Snow

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The Smart Road's snowmaking equipment and facilities include a 1,892,706-liter (500,000 gallon) water tank and 80 aluminum snow towers. The towers span a 0.8-km (0.5-mi) section of the road and are spaced at intervals of approximately 10 m (33 ft). At 12.2 m (40 ft) long, the towers can be adjusted for use at various heights, but they are most commonly used at a height of 7.6 m (25 ft). At full capacity, the towers can produce up to 0.3 m (1 ft) of snow per hour.

The snowmaking system uses municipal water; therefore, the water tank is used to avoid placing large burdens on municipal facilities during snow production. During snowmaking, water from the tank is pumped at 206.84 Newtons per square centimeter (N/cm²) to 344.74 N/cm² (300 to 500 psi). The amount of water used varies according to the size of the nozzle used on the snow towers. Each snow tower uses four nozzles. Depending on weather conditions and snow quality, the system uses between 4,295,000 to 6,750,000 liters per hectare-meter (140,000 to 220,000 gallons of water per one acre foot) of snow. In addition to its function as a buffer for municipal water facilities, the water tank is used to avoid water shortages and subsequent problems during snow production.

The water arrives in the tank at approximately 10 °C to 21.11 °C (50 °F to 70 °F). To produce snow, the water must be cooled to approximately −1.11 °C to 0 °C (30 °F to 32 °F) before being pumped to the snow towers. During snow production, the chilled water is drained out of the tank into a wet well from which it is drawn by pumps to the snow towers. The water travels through the ground through a concrete-lined pipe, which acts as an insulator to lessen the transfer of ground heat to the water.

The quality and quantity of the snow produced depends largely on the ambient weather conditions. The ideal snowmaking conditions are dry and cold; however, temperatures of −6°C (21.2 °F) and below are optimal, regardless of the humidity level. As temperatures rise, lower humidity levels are required to produce snow. For example, high-quality snow can be produced at temperatures as high as −2 °C (28.4 °F), but only at humidity levels of 20 percent or below. As the temperatures and humidity levels rise, the quality of the snow produced begins to dramatically decrease. Snow can still be produced at temperatures as high as 2.79 °C (37 °F), at humidity levels of 10 percent or less.

Snow created on the Smart Road has only a short distance to form, grow, and strengthen; therefore, it is extremely important that the water emitted from the snow towers is on the verge of freezing. After it is sprayed from the nozzles, it is frozen quickly by the supercooled, compressed air that is blown from the air jets on the nozzles.


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