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Road Width

Road rights-of-way should be wide enough to enhance surface drying during wet periods. This will reduce rut development and soil movement. Road surfaces should be at least 10 feet wide but no wider than necessary to be functional. Usually a width of 12 to 14 feet is adequate for a single-track road. Some roads that support frequent and heavy traffic should be 16 feet wide with 24-foot turnouts every 500 feet for two-way traffic.

The minimum shoulder width should be 2 feet on each side of tread width. Increase all widths by 4 feet if traffic from towed trailers of any kind is expected. Brush, trees and roots should be removed from the part of the right-of-way needed for surfacing and ditches (if ditches are used). Beyond that, clear 2 to 3 feet or more of brush and trees on either side of ditches to enhance surface drying.

Surface drying is critical to the life and use of unpaved roads. The best tool for this is the sun so place your roads to get the most direct sunlight. In some areas the best orientation for roads will be east-west, especially if the sun is directly overhead during parts of the day when the road will be used most often. Otherwise, north-south roads will dry better if there is a wide right-of-way since there will be some direct sunlight most everyday regardless of the season.

Curves Curves in roads can be horizontal, vertical or a combination of the two. Since slopes greater than 5 percent aren't generally found on wet soils, the only curves needed are horizontal. The basic rule is to have a minimum radius horizontal curve for 35 feet for short-body vehicles and 50 feet for tractor trailers. These curves are acceptable for roads that will have only low-volume traffic.

In higher traffic areas, curves should have a radius of 100 feet or more. This increases visibility to about 200 feet and allows for higher but equally safe vehicle speeds since drivers have a longer response time to apply brakes. Speeds greater than 20 mph will permit more production if loads are being moved frequently.


next up previous
Next: Obtaining Materials Up: Design, Layout, and Preparation Previous: Location and Marking
Warnell School of Forest Resources