NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION
PRACTICE STANDARD
ACCESS ROAD (Feet)
CODE 560
DEFINITION
A travel-way for equipment and vehicles constructed as
part of a conservation plan.
PURPOSE
To provide a fixed route for vehicular travel for resource
activities involving the
management of timber, livestock, agriculture, wildlife
habitat, and other conservation
enterprises while protecting the soil, water, air, fish,
wildlife, and other adjacent natural
resources.
CONDITIONS WHERE PRACTICE APPLIES
Where access is needed from a private or public road or
highway to a land use enterprise or conservation measure, or where travel ways
are needed in a planned land use area. Access roads range from seasonal use
roads, designed for low speed and rough driving conditions, to all-weather
roads heavily used by the public and designed with safety as a high priority.
Some roads are only constructed for a single purpose; i.e. control of forest
fires, logging and forest management activities, access to remote recreation
areas, or access for maintenance of facilities.
CRITERIA
Access roads shall be designed to serve the enterprise or
planned use with the expected vehicular or equipment traffic. The type of
vehicle or equipment, speed, loads, soil, noise, climatic, and other conditions
under which vehicles and equipment are expected to operate need to be
considered. Planned work shall comply with all federal, state and local laws
and regulations. Access roads hall meet all local codes, ordinances and
specifications related to roads and driveways. Where general public use is
anticipated, roads shall be designed to meet applicable federal, state and
local criteria. Free access both up and down a stream network is necessary to
protect valuable fisheries resources. One fish barrier in a stream can
seriously affect the entire fish population in that stream. An improperly
installed culvert may create such a barrier. The following is a list of general
criteria that should be followed when designing a culvert where fish passage is
essential.
1. Resting pools shall be provided above and below the
culvert.
2. Each jump must be negotiable by the smallest fish
species, usually not greater than one foot for an adult trout.
3. Water velocity must be less than the sustained swimming
speed of the smallest fish passing through the culvert. The recommended maximum
velocity is four feet per second for trout.
4. Culverts longer than 100 feet shall be provided enroute
rest areas or the velocities should be reduced below the established minimums.
Location. Roads shall be located to serve the purpose intended, to
facilitate the control and disposal of surface and subsurface water, to control
or reduce erosion, to make the best use of topographic features, and to
include scenic vistas where possible. The roads should generally follow natural
contours and slopes to minimize disturbance of drainage patterns. Roads shall
be located where they can be maintained and where water management problems are
not created. To reduce potential pollution, roads shall be located away from
watercourses. Utilize buffers where possible to protect waterbodies.
Alignment. The gradient and horizontal alignment shall be adapted to
the intensity of use, mode of travel, the type of equipment and load weights,
and the level of development. Grades normally should not exceed 10 percent
except for short lengths of up to 100 feet. Maximum grades of 18 percent should
only be exceeded if necessary for special uses such as logging roads, field
access
roads, fire protection roads or other roads not accessible
for use by the general public. Water control immediately above steep grades
will generally be needed. When necessary to keep within maximum allowable
grades, road will be located diagonally across the slope. The minimum radius of
curvature of centerline for turn arounds and curves shall be 40 feet for cars
only and 50 feet for cars with trailers up to 30 feet long. The use of minimum
radius curves should be avoided if longer radius curves can be obtained at
practically the same cost. For stream crossings (fords), the road should be
aligned so that it crosses perpendicular to the channel as much as possible and
under
the following conditions:
• Water depth is less than 3 feet.
• The streambed has a firm rock or coarse gravel bottom,
and the approaches are low and stable enough to support traffic.
Stabilize the approaches by using nonerodible materials
that extend at least 50 feet on both side of the crossing. The State Stream
Alteration Engineer shall be notified on all stream crossing projects.
Width. The minimum width of the roadbed is 14 ft for one-way traffic and 20
ft for two-way traffic. The roadbed width includes a treadwidth of 10 feet for
one-way traffic or 16 feet for two-way traffic. Each type of road also requires
2 feet of shoulder width on each side. Single-lane logging or special-purpose
roads can have a minimum width of 10 feet, with greater widths at curves and
turnouts.
The two-way traffic width shall be increased approximately
4 feet for trailer traffic. The shoulder width may be either gravel or grass.
Brush and trees shall be removed from the roadway to a minimum width of 14 to
16 feet prior to grading. Minimum widths of 14 feet are acceptable on tangents
with fairly level sections without appreciable depth of cut or fill. Minimum
widths of 16 feet shall be used on all curves, side hill sections or areas of
substantial cut or fill. Sufficient side
clearance shall be allowed for clear passage of trucks
along the finished road. Generally, a minimum of two feet of cleared area is to
be maintained from the edge of the graded surface. Turnouts shall be used on
single lane roads where vehicles travel in both directions on a limited basis.
Where turnouts are used, road width shall be increased to a minimum of 20 feet
for a distance of at least 30 feet. Turnouts shall be spaced every 200 to 500
feet. Where sight distances exceed 1000 feet, turnouts may be spaced at 1000
feet.
Side Slopes. All cuts and fills shall be designed to have stable slopes
of a minimum of 2 horizontal to 1 vertical on heights of less than 4 feet. For
short lengths, rock areas, or very steep hillsides, steeper slopes may be
permitted, if soil conditions warrant and special stabilization measures are
installed. Areas with geological conditions and soils subject to slides shall
be avoided or treated
to prevent slides.
Drainage. The type of drainage structure used will depend on the
intended use and runoff conditions. Culverts, bridges, fords, or grade dips for
water management shall be provided at all natural drainage ways. The capacity
and design shall be consistent with sound engineering principles and shall be
adequate for the class of vehicle, type of road, development, or use. When a
culvert or bridge is installed in a drainage way, its inimum capacity shall
convey the design storm runoff without causing erosion or road overtopping.
Table 1 lists minimum design storm frequencies for various road types.
Table 1
Road Type Storm
Frequency
An erosion-resistant low point or overflow area may be
constructed across the access road to supplement culvert capacity on nonpublic
use roads. Culverts, bridges, fords and hardened overflow areas should be
installed so the road crossing does not significantly impact fish migration.
Roadside ditches shall be adequate to provide surface drainage for the roadway
and deep enough, as needed to serve as outlets for subsurface drainage. At a
minimum, the roadside ditch shall be 1.0 foot below the top of road surface to
provide internal drainage. Ditch channels shall be designed to be on stable
grades or protected with structures or linings for stability. Water-breaks or
water-bars may be used to control surface runoff on low-intensity use forest,
ranch or similar roads. On steep grades where runoff and erosion is anticipated
down the road, water bars should be considered. Water bars must be constructed
of materials that are compatible with the use and maintenance of the road
surface. Water bar discharge areas must be well vegetated or have other erosion
resistant materials. See Figure 1 Recommended Spacing of Relief Culverts and
Water Bars Based on Soil Type. Roadbed drainage shall be provided at all seep
areas and high water table areas. The depth, spacing, outlets, and size of
roadbed drains shall be such as to keep the water table at least 24 inches
below the surface. Surface crowning can also help direct road runoff into the
side drainage ditches. The centerline of the access road shall be crowned at
least 3 inches higher than the shoulder. Unobstructed flow into the ditches
must be maintained to prevent flows from causing roadside erosion. Provide a
turnaround at the end of dead end roads. In some areas, turnarounds may also be
desirable for stream, lake, recreation, or other access purposes. Provide
parking space as needed to keep vehicles off the road or from being parked in
undesirable locations.
Surfacing. Access roads shall be given a wearing course or surface
treatment if required by traffic needs, soil, climate, erosion control, or
particulate matter emission control. The type of treatment, if
needed, depends on local conditions, available materials,
and the existing road base. If these factors or the volume of traffic is not a
problem, no special treatment of the surface is required. On weak bearing
capacity soils such as silts, organics, and clays, the surface treatment should
be underlain with a geotextile material specifically designed for road
stabilization applications when the road is used on a regular basis. Unsurfaced
roads may require controlled access to prevent damage or hazardous conditions
during adverse climatic conditions. Toxic and acid-forming materials shall not
be used on roads. This should not be construed to prohibit use of chemicals for
dust control
and snow and ice removal after considering potential
impacts on stabilizing vegetation. Utilize additional conservation practices to
reduce the potential for generation and transport of particulate matter
emissions.
Construction Operations. Construction operations should be
carried out in such a manner that erosion and air and water pollution are
minimized and held within legal limits. Construction shall include the
following requirements as necessary for the job:
1. Trees, stumps, roots, brush, weeds, and other
objectionable material shall be removed from the work area.
2. Unsuitable material shall be removed from the roadbed
area.
3. Grading, sub-grade preparation, and compaction shall be
done as needed.
4. Surfacing shall be done as needed.
5. Measures must be in place to limit the generation of
particulate matter during construction.
Traffic Safety. Passing lanes, turnouts, guardrails, signs, and other
facilities as needed for safe traffic flow shall be provided. Traffic safety
shall be a prime factor in selecting the angle and grade of the intersection
with public highways. Preferably, the angles shall be not less than 85 degrees.
The public highway shall be entered either at the top of a hill or far enough
from the top or a curve to provide visibility and a safe sight distance. The clear
sight distance to each side shall not be less than 300 feet or as required by
local regulations.
Erosion Control. If soil and climatic conditions are favorable, roadbanks
and disturbed areas shall be vegetated as soon as possible and skid trails,
landings, logging, and similar roads shall be vegetated after harvesting or
seasonal use is completed (see Critical Area Planting-342). If the use of
vegetation is precluded and protection against erosion is needed, protection
shall be provided by nonvegetative materials, such as gravel or other organic
or inorganic material (see Mulching 484), or in accordance with local
regulations.
Spacing (feet) Gravely Soils Sands, Silts & Clay
Soils. Roadside
channels, cross drains, and
drainage structure inlets and outlets shall be designed to
be stable (see Structure for Water Control). If protection is needed, riprap or
other similar materials shall be used. Watercourses and water quality shall be
protected during and after construction by erosion-control facilities and maintenance.
Filter strips, water and sediment control basins, and other conservation
practices
shall be used and maintained as needed.
CONSIDERATIONS
Consider visual resources and environmental values during
the planning and designing of the road system. When available, consider using
organic biodegradable materials as a surface treatment.
Access roads should be located where minimal adverse
impacts will affect wetlands, waterbodies wildlife habitat, and air quality.
Consideration should be givento the following:
• Effects on downstream flows or aquifers that would
affect other water uses or users.
• Effects on the volume and timing of downstream flow to
prohibit undesirable environmental, social, or economic effects.
• Short-term and construction-related effects of this
practice on the quality of on-site downstream water courses.
• Overall effects on erosion and the movement of sediment,
pathogens, and soluble and sediment-attached substances that would be carried
by runoff from construction activities.
• Effects on wetlands and water-related wildlife habitats
that would be associated with the practice.
• Establishing vegetation on road shoulders wider than the
2-4 ft.
• Limiting the number of vehicles and vehicle speed will
reduce the potential for generation of particulate matter and decrease safety
and air quality concerns.
PLANS AND SPECIFICATIONS
Plans and specifications for constructing access roads
shall be in keeping with this standard and shall describe the requirements for
applying the practice to achieve its intended purpose. An aerial
photo/map of Access Roads greater than 600 feet shall be
kept in the clients folder.
OPERATION AND MAINTENANCE
An operation and maintenance plan will be developed and
carried out for the life of the practice:
1. Inspect culverts, roadside ditches, water bars and
outlets after each major runoff event and restore flow capacity as needed.
2. Minimize the damage to vegetative buffers adjacent to
the road when it is necessary to chemically treat the road surface to maintain
erosion protection.
3. Maintain vegetated areas in adequate cover to meet the
intended purpose(s).
4. Fill low areas in travel treads and regrade, as needed,
to maintain road cross section.
5. Inspect roads with water-bars periodically to insure
proper cross section is available and outlets are stable.
6. Conservation practices that limit particulate matter
emissions should be
incorporated into long-term maintenance plans.
7. Trees, brush and other woody vegetation along the
access road that is obstructing line of site or the overall maintenance shall
be removed.
REFERENCES
• Fish Passage Design at Road Culverts, Washington
Department of Fish and Wildlife, 4/3/99.
(http://www.wa.gov/wdfw/hab/engineer/cm/culvertm.htm)
• A Landowner's Guide to Building Forest Access Roads,
USDA Forest Service (NA-TP-06-98) Richard L.Wiest, Northeastern Area State
and Private Forestry.
Conservation practice standards are reviewed periodically,
and updated if needed. To obtain the current version of this standard, contact
the Natural Resources Conservation Service.
NRCS-VT
APRIL 2004
