Forest Road Engineering Guidebook - Ministry of Forests

Road design specifications consist of alignment elements (e.g., horizontal
curvature, vertical curvature, road grade, and sight distance) and cross-section
elements (e.g., full or partial bench construction, sidecast construction, road
width, angles of repose for stable cut slopes, ditch dimensions, drainage
specification, and clearing widths).
Geometric road designs include plans, profiles, cross-sections, and mass haul
diagrams showing the optimum balance of waste, borrow, and endhaul volumes.
The designs are generated from the route selection process and the
location survey. From the location survey information, a road centreline
(L-Line) is designed for vertical and horizontal alignment, earthwork quantities
are calculated, and a mass haul diagram is produced to show the optimum
placement of excavated material.
Figure 2 shows a typical road cross-section and the terminology used to
describe cross-section elements.
Factors to consider in road design
Road design should consider the following factors:
Forest Road Engineering Guidebook
General considerations:
• intended season and use of the road (design vehicle configuration for
load and alignment, and traffic volume)
• climate (heavy snowfall areas, heavy rainfall areas, etc.)
• design service life of the road
• user safety
• resource impacts
• economics
• road alignment (horizontal and vertical geometry)
• junctions with existing roads
• road width (turnouts and widenings).
Soils, road prism geometry, slash disposal:
• the measures to maintain slope stability if the road will cross areas with
a moderate or high likelihood of landslides (also see “Geometric road
design requirements” below)
• soil types (including the use of appropriate conversion factors to adjust
for swell and shrinkage of materials)
• cut and fill slope angles
• clearing widths
• slash disposal methods
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