Planning and location are the most important aspects of road development. Poor planning or location is associated with the following most common causes of road failure (Furniss et al. 1991):
Improper placement and construction of road fills
Insufficient culvert sizes
Very steep road grades
Improper placement or sidecast of excess materials
Removal of slope support by undercutting
Altering drainage by interception and concentrating surface and subsurface flows.
Because roads are long-term features, their location must be carefully chosen, to meet the landowners need for safe access, avoid long-term maintenance problems, reduce potential for degrading water quality, and minimize costs over the short and long term. At a minimum, road locations should be flagged and approved by the landowner in advance of any construction, including all temporary road locations.
|This section on road planning
and location tells you how to map out a road, then how to field check the location and how
to mark it on the ground.
The key to good road planning is to gather as much information as possible on the area to which access is needed. If subcontracting for road building, this recommendation still applies. The subcontractor generally will not know the area as well as you do. In most cases, maps and soils information are available. Contour maps are useful on all but the flattest terrain and can usually be obtained from local, county, or State governments. They are also available from the U.S. Geological Survey. The USDA Natural Resources Conservation Service (NRCS) will be able to provide soils information for your area.
When initially requesting maps, also request information from the State or county about rights-of-way requirements if the proposed road has the potential of entering onto a State or county road. The necessary right-of-way requirements can be met as you proceed in the planning process.
|After gathering the maps and
related information, indicate control points on the maps. A control point is simply a land
feature that limits your choice of road location. Control points can force a road through
a given location or prevent the road from being built in a given location. The following
is a list of control points with some general comments about each one. The list is not
all-inclusive and is not intended to be.
above or below these. If you have to go through them, see if the rock can be ripped or
broken because this will be less costly than blasting.
RidgesThese provide good road locations.
SaddlesLook for these as points to cross ridges.
BenchesThese are good road locations and also provide a good point for location of junctions, switchbacks, and landings.
Wet meadowsAvoid. If they have to be crossed, see the section on Recommendations for Wetland Forest Roads.
Beginning and ending of roadUsually known.
Property linesBe sure of property line locations.
StreamsAvoid crossing streams, if practical. If unavoidable, look for the best places to cross, considering the following (Furniss et al. 1991):
Always cross at right angles.
Cross at points where the stream is narrow.
Minimize the number of crossings.
Do not build in the bottom of a draw.
Leave a buffer zone of undisturbed ground between the road and streambed, where the road runs parallel to the stream.
|...||Table 1 gives recommended buffer widths
for Minnesota, which are consistent with the recommendations of Haussman and Pruett (1978)
for the northeastern United States. Since recommended buffer widths vary, check the
regulations in your State.
Approaches to public roads and highways, power lines, or other easementsState, Federal, and county regulations require permits to enter public roadways. Locations of approaches may be restricted for safety or other reasons. Road access easements need to be checked and approved before you proceed any further.
|Other items to consider, which are too broad to be called control points, are aspect and soils.|
|AspectSouth- and west-facing slopes will
usually be drier and free of snow sooner in spring. This may be a minor consideration in
your area depending on soils, precipitation, and topography.
SoilsCheck the local soil survey to determine the types of soil in your area. Determine which soil characteristics react to road building and how. The county engineer or NRCS engineer can answer questions on soils in your area. Certain plants give an indication of problem soils. Contact your State agronomist for information on indicator plants for problem soils. NRCS may also have information available on plant identification.
|As these control points are found, locate
them on a contour map and label them. You may not find all the control points in the
initial investigation, so you should update your map as you progress through the planning
|Using the contour map, pencil in
a tentative road location using your beginning and ending points as a start. Draw the road
in the desired location that accesses the desired area making sure control points are
either hit or missed. Remember, control points can be points where the road should go or
places to avoid (Figure 1).
Once you have mapped a tentative road location determine the grade of the road. See Figure 1, for example. This will give you a rough idea of how steep the road will be and will point out sections of road where the grade may be too steep. If the grade is too steep, move the road until a satisfactory grade is obtained. Look for any additional control points you were not aware of and add them to the maps. Determine the grade for each road segment between control points, using either topographic maps or the following formula for determining average grade for the entire road.
between segments of road
----------------------------------- =grade x 100 % grade
Length of road
Figure 1. Map out the road by locating and labeling control points on a contour map, which allows you to check the road grade.
|Grade problems will be evident at this point. If a segment shows a grade greater than 12 percent for over 300 feet, consider another road location. Under good conditions, the road grade would be less than 8 percent. When necessary, however, short steep pitches under 300 feet in length are acceptable.||
|Begin field checking the road location after it is
mapped, by locating on the ground all the control points indicated on the map. This field
check involves tying ribbon along the proposed location. The ribbon location is called the
tagline, which is located on the approximate grade as drawn on the map. An abney or
clinometer that shows percent grade will be needed to transfer the mapped road to the
ground. If these other tools are not available, the grade meter at the back of this guide
can be used (West Virginia Dep. Agric., no date).
To locate your tagline use a clinometer or abney and tie ribbons at eye level. Move ahead towards the next control point and look back to the previous ribbon, then tie another ribbon at eye level or at the height of the instrument being used. Distance can be determined from the map.
|Two types of curves are commonly found in roads: horizontal and vertical curves. A horizontal curve is needed where the road changes direction. If the direction change is dramatic, the curve will need to be large enough to allow a log truck to negotiate the turn. A vertical curve is created where the grade changes from downhill to uphill or uphill to downhill. Planning vertical curves is also important because they can be made so abrupt that a log truck could high center at a crest. Some simple methods for laying out curves follow. Certain circumstances require switchbacks, which are also described in detail.||
Figure 2.The center stake method of creating a horizontal curve is limited to use on gentle terrain with good visibility. (Redrawn from Figure 2.4-1, Darrach et al. 1981)
|Horizontal Curve Layout
Two simple procedures are described for creating a horizontal curve. The first is the center stake method; the second is the stick method. The center stake method is limited to gentle terrain and good visibility. The stick method is more suited to difficult sites.
|A curve should always meet the
minimum turning requirements of the vehicles expected to use the road. Log trucks require
a minimum of a 50-foot radius curve. Flatbed trucks used to haul heavy equipment (lowboys)
must have at least a 70-foot radius curve. Grade should be adjusted through the curve to
provide for safe handling of heavy equipment. See Table 2 for grade adjustments.
Simple curves may be staked on the ground with a stick and a tape. For directions see the box on Curve LayoutStick Method. Using a 25- or 50-foot staking distance, consult Table 3 for the proper stick length to set the radius shown. Figure 3 shows the process.
|Adjusting for Topography and Grade
The horizontal curve layout description assumes the area is flat. Seldom is this the case. Measurements of length must then be adjusted to compensate for slopes.
Where the distance being measured is short, the tape can be held level for one measurement of the entire distance. Where the distance is longer than convenient for this leveling method, measure the distance in segments. Adjust the measured slope length by using Table 4.
Grade may be maintained around the curve by running a line with the desired slope for the distance of the curve. This line will often be away from the center line of the road due to the topography (Figure 3).
Where two control points cannot be connected by a road with maximum grade in a single direction, a switchback is required. It is placed at the point where there is enough room to make a switchback. Good switchback sites are areas with little side slope where the loop may be constructed with the least excavation. There should be no more excavation of the hillside above the switchback than is needed to fill along the lower side of the switchback.
Reduce the grade of the road coming into and out of the switchback, to help maintain a gentler grade through the curve. The curve itself should not exceed an 8 percent grade. For instructions see Figure 4 and the box on Constructing a Switchback.
|Grade Separation and Vertical Curves|
|Care must be taken not to
create a spur that branches off a road too abruptly leaving little room for the grades to
separate. Both the main road and spur must have the same grade for a distance equal to at
least the sum of half the width of each (Figure 5). For example, a 10-foot-wide spur and a
12-foot-wide road should both have the same grade for a distance of 11 feet.
Figure 5. A main road and spur must have the same grade for a distance equal to at least the sum of half the width of each. (Redrawn and adapted from Figure 2.4-7, Darrach et al. 1981)
|Vertical curves may either crest
or sag. To provide a smooth transition, adjust or offset the height of the road at the
point where the uphill and downhill slopes meet. A transition of 200 horizontal feet is
sufficient for a simple access road. A vertical offset involves cutting a crest or filling
a sag (Figure 6). Table 5 provides additional solutions for 200-foot curves.
|Figure 6. A vertical cut provides a smooth transition on a crest (top), and a vertical fill provides a smooth transition on a sag (bottom). (Redrawn from Figures 2.4-8 and 2.4-9, Darrach et al. 1981)|
Figure 7. A turnout should be at least 10 feet wide, to allow two trucks to pass safely. (Redrawn from Figure 2.4-10, Darrach et al. 1981)
Figure 8. Turnaround design should consider drainage.
Turnouts and Turnarounds
A turnout is needed when more than one vehicle will use the road at the same time. A turnaround provides a convenient, safe area to turn vehicles at the terminus of a dead end road.
For low speed, single lane roadways, turnouts are usually set within sight of each other. A standard plan for a turnout is shown in Figure 7. Turnout width is set with enough room to allow two trucks to pass safely. The width is never less than 10 feet. Leads into and out of turnouts are typically a minimum of 25 feet long.
Turnarounds are usually located within sight of the roads end on fill. Common dimensions of a turnaround are shown in Figure 8.
Five road cross-sections typically are used in road construction: crowned fill, crowned turnpike, outslope, inslope with ditch, and crowned and ditched (Figure 9). The choice of which cross-section to use depends on the drainage needed, soil stability, slope, and the expected volume of traffic on the road. You can use these cross-sections in combination as the terrain changes or as drainage problems are encountered.
Crowned fill section is for use on flat ground where water standing on a road surface may be a problem. Outslope section is for use on moderate slopes for low volume roads and stable soils. Outsloping is not recommended on roads requiring winter logging. Inslope with ditch section is for use on steep hills, areas with fine textured soils, winter logging, and areas where drainage is necessary. Crowned and ditched section is for high volume roads on steep side hills.
Where roads cross lands of other owners, permission to cross must be obtained. It is always advisable to obtain written agreements or to record easements. Written agreements and recorded easements protect the interests of all parties.
Figure 9. The choice of cross-section for a road or section of a road depends on drainage needs, soil stability, slope, and expected traffic volume. Dashed lines indicate natural land contours, and solid lines indicate constructed road. (Redrawn and adapted from Michigan Department of Natural Resources 1994, p. 23)
|A right-of-way agreement should define the road location,
its points of ingress and egress, and width. All other pertinent information should be
carefully noted. A simple survey may be desirable. Such conditions as the maintenance of
fences, gates, and other improvements should be clearly specified. Monetary considerations
or other forms of payment requested by the grantor should also be made a part of the
agreement. Before executing and recording a right-of-way agreement, consult an attorney.
Should the road end on the right-of-way of a public secondary or primary highway, the local highway department should be contacted. State highway departments have regulations governing the entry of private roads onto public roads.
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