DESIGN OF ROADS IN SNOW DRIFTING AREAS

This report describes the use of climatic data for the design of highways situated in areas with drifting snow. It also concentrates on the cross sectional design of such highways. The winterproblems in connection with all- seasonal highways may be divided into the following four groups: The problems of: (1) Snow clearing, (2) Sight, (3) Operation, and (4) Security. With the strong and effective maintenance equipment available, it seems that the problems with sight and avoidance of panic after minor accidents are the main issues to be solved. The relation between the sightlengths and the wind conditions have been studied along the Haukeli road (E76) in the southern part of Norway. These studies show that free traffic had to be closed down and convoys arranged, under the following conditions: (1) Wind speed exceeding 13 meters per sec with simultaneous snowfall, and (2) Wind speed exceeding 17 meters per sec without snowfall. In convoys, cars are permitted to pass the mountain region only when accompanied by a snowclearing truck. Three methods for snowdepth surveying are tested and described: (1) The traditional method of snowdepth measuring combined with tachymetric surveying; (2) The photogrammetric method: comparing summer and winter air photos of the surface; and (2) A method using botanical information. The length of the snowcover is a critical factor for the plants and is reflected in the distribution of the particular species. The report concludes that a combination of the tachymetric and botanical methods in generally recommended for the surveying of snowdepths when planning mountain highways. To find the optimum shape of the cross section of highways in snow drifting areas, models where tested in a water flume. Sand with grain diameter in the range of 0.15 to 0.30 millimeters was found to give the best fulfillment of the laws of simulitude. The model scale used was 1:100 and the water velocity in the flume was 1.3 meter per sec. This speed corresponds to a wind speed of 16 meters per sec. The results from practical and model experiment have lead to the following recommendations for the cross sectional design of a mountain highway: 1. The height of a fill should at least equal the mean snowdepth in the area. In areas with extremely bad climate, i.e. more than 15 days pr months with windspeed above 11 meters per sec, 50 centimeters should be added to the recommended height. The top of the fill should be well rounded. The radius of curvature should equal twice the height of the fill. The slope of the fill wassl may be as steep as 1:2 when the top is rounded. Guardrails should be avoided. They can be replaced by the use og gentle slopes. 2. Snow clearing is quite difficult in cuts. Therefore it is extremely important to provide enough room for snow storing in cuts. The best way to accomplish this is to make one of the cut slopes horizontal. If the wind direction is predominantly against the terrain slope, the dam side should be designed as specified for fills. The ditch on the cut side should be made more than 3 meters wide. If the wind blows downhill, it is necessary to decrease the cut slope to prevent the traffic lane from lying in an eddy zone. The angle between a line drawn from the surface of the snow cover at the top of the cut slope to the road edge, and the natural slope should be less than or equal to 1:6.5. In areas with moderate snowdrift, it is sufficient to widen the cut with a ditch, e meters wide. Snow gathered in this ditch has to be cleared away after each major snow storm. /Author/

  • Corporate Authors:

    Institutt for Veg-OG Jernbanebygging

    Trondheim University
    Trondheim,   Norway 
  • Authors:
    • Norem, H
  • Publication Date: 1974-5

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 131 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00096815
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 30 1975 12:00AM