TECHNICAL PAPER #45
 
                            UNDERSTANDING LOW-COST
                                ROAD BUILDING
 
                                      By
                        Joe Barcomb & David K. Blythe
 
                              Technical Reviewer
                        Jonathan Kibee & Henry Parker
 
                                Illustrated By
                                   Rick Jali
                                    
                                     VITA
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel: 703/276-1800 . Fax: 703/243-1865
                          Internet: pr-info@vita.org                  
 
                     Understanding Low-Cost Road Building
                             ISBN: 0-86619-259-X
                 [C]1986, Volunteers in Technical Assistance
                                 Revised 1990
     
 
                                   PREFACE
 
This paper is one of a series published by Volunteers in
Technical Assistance to provide an introudction to specific
state-of-the-art technologies of intrest to people in developing
countries.  The papers are intended to be used as guidelines to
help people chooe technologies that are suitable to their
situations.  They are not intended to provide construction or
implementation details.  People are urged to contact VITA or a
similar organization for further information and technical
assistance if they find that a particular technology seems to
meet their needs.
 
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis.  Some 500 volunteers were involved in the
production of the first 100 titles issued, contributing
approximately 5,000 hours of their time.   VITA staff included
Patrice Matthews handling typesetting and layout, and Margaret
Crouch as editor and project manager.
 
Joe Barcomb is a VITA Volunteer who is a civil engineer with the
U.S. Forest Service.  His co-author VITA Volunteer David K.
Blythe, is a civil engineer and Associate Dean for Continuing
Education for the Department of Engineering, University of
Kentucky in Lexington.  The reviewers are also VITA Volunteers.
Jonathan Kibbee is a lawyer with Lord, Day and Lord in New York
City who has worked in Haiti on a water control and development
project.  Henry W. parker, retired professor emeritus of civil
engineering at Stanford University, has had extensive road
construction experience in Colombia and Venezuela.   Illustrations
were done by VITA Volunteer Rick Jali.
 
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries.   VITA
offers information and assistance aimed at helping individuals
and groups to select and implement technologies appropriate to
their situations.  VITA maintains an international Inquiry
Service, a specialized documentation center, and a computerized
roster of volunteer technical consultants; manages long-term
field projects; and published a variety of technical manuals and
papers.
 
                     UNDERSTANDING LOW-COST ROAD BUILDING
              by VITA Volunteers Joe Barcomb and David K. Blythe
 
Roads vary from trails to major hard-surface highways.   Depending
on the local climate and materials available for construction,
roads may sometimes be open to traffic for only part of the year.
A year-round road is often more expensive to build, and may not
always be necessary.  As a general rule, road construction in
rural areas can be done at relatively low cost because, compared
to city roads, fewer people and vehicles travel on rural roads.
However, rural roads must be well designed, properly constructed,
and continually maintained.
 
I. QUESTIONS TO CONSIDER BEFORE BUILDING A ROAD
 
Before you begin to make decisions about designing, building, or
improving a road or trail system, you should consider the following
questions:
 
1.   Why do people want a road? Do they want to take produce or
     home industry products to market? Do they want access to
     medical assistance or other advanced technologies? Is a trail
     adequate to move people, goods, or animals, or is a full-scale
     road necessary? Whenever possible, try to get the local
     people involved in the design and construction of the road or
     trail.   People will usually want to help build what they feel
     is needed, and people who have participated in the construction
     of roads or trails are likely to want to maintain them.
     If, on the other hand, you are not responsive to people's
     needs, they are not likely to provide you with much help.
 
2.   Where does the road need to go? Determine the route that best
     serves the users, getting them from their starting point to
     their major destination.  If some intermediate points can be
     reached by going only slightly out of the way, then try to
     incorporate them also.  Destination points are usually large
     villages or better transportation facilities.
 
3.   How much of the year is the road used and how heavily is it
     used? A road that is open year-round is often desirable but
     much more expensive to construct than one open only part of
     the year.   Whether this extra cost is justified will depend in
     part on how much of the year the less expensive road would be
     unusable.   For example, if a road crosses a riverbed that has
     water in it only three weeks out of the year, is it worthwhile
     to build a bridge? Generally speaking, the more traffic
     a road system carries, the more time and money may be spent
     on its construction.
 
4.   What kinds of goods need to be moved? Are they self-propelled
     (like trucks or cattle) or stationary (like bulk rice)? Are
     they small or bulky? You do not need the same type of road to
     transport jewelry as to transport grain.  The jewelry could be
     carried by a mule on a seasonal trail, while the grain might
     require a road that was passable by truck under a variety of
     weather conditions.  Animals can be herded along a trail or
     road, but logs might require a truck road.
 
5.   How do people currently travel and move their goods? Will
     there be a shift in the type of products coming from the
     outside world or from the local source? If not, then you
     should consider making limited improvements to the present
     road, for example, or a seasonal road into a year-round road.
     Improving a road or trail system significantly may not be
     warranted, especially if the local people do not have the
     vehicles or the operating skills to take advantage of a more
     highly engineered road.
 
6.   What kinds of vehicles are available to move people and
     goods? Are motorized vehicles used? If so, what size are
     they? If for example, motorbikes with a sidecar are the only
     vehicles used, a road with wide lanes is unnecessary.  Buses
     and small trucks need a wider road than do animal-drawn
     carts.   And an animal carrying a load on its back may not need
     a road at all.
 
7.   What is the physical terrain? Plan to use the terrain to your
     best advantage.  Building roads on side slopes of 15 to 45
     percent minimizes construction costs.  Conversely, building
     roads on steep terrain usually means higher construction
     costs, because of the high volume of earth and rock that must
     be dug out and removed.  Extremely flat ground also usually
     means higher construction costs, because measures must be
     taken to prevent floods and washouts.  Rivers and streams
     should be avoided where possible since they may be costly to
     bridge.   It is also wise to avoid other obstacles such as rock
     outcrops, ledges, highly erosive soils, and swampy places,
     since they are apt to create difficulties in construction.
 
8.   What technical skills are available? Are there personnel who
     have worked on similar projects in this or other areas who
     can form a cadre? Sources of external funding can often also
     make skilled technicians available.
 
9.   What equipment is available? Do you have power-driven equipment
     or are you limited to hand tools or animal-driven equipment?
     How might existing tools and methods be adapted to the
      construction process?
 
10.  What financing is available? Is there some form of local
     taxation that can raise the funds for building or improving
     the road system? If not, are funds available from other
     sources? How much money can be raised from all sources? Will
     the cumulative funds from all sources meet the needs of the
     project, or will the project have to be scaled down? Sometimes
     outside organizations will donate funds equal to the
     value of local donations of labor.
 
11.  What permissions will be required? Will you need written
     permission to cross land owned by other people, and will you
     need to secure any permits for public road access? You might
     need to get a right-of-way to change the course of a road, to
     widen it, or to block the flow of a stream.  Such permissions
     should be obtained before construction begins, to avoid
     costly delays.
 
12.  How will the road system be maintained after it is completed?
     If local personnel are to maintain it, do they have a vested
     interest in doing so, or are they likely to let the road fall
     into such a state of disrepair that it will have to be rebuilt?
     Remember, if you build a system that does not meet
     people's needs, you can expect little commitment on their
     part to maintaining the system.
 
II. PLOTTING THE COURSE
 
Surveying
 
Before construction begins, the proposed road or trail location
is plotted or sketched on paper.   The next step is to walk the
entire length of the proposed route to become familiar with the
topography and ground conditions.   The proposed route is then
surveyed to measure its slope (also called its grade or gradient)
at a number of points along its course.   If the slope between the
starting point of the survey and the next point along the course
is too steep, the surveyor adjusts the route uphill or downhill
until the desired grade is obtained.   The two points are then tied
in with markers.  This process is repeated until the entire course
is marked.  The marked line represents the center line of the
proposed road.  Marking can be done with blazes (spots or marks
made on trees), paint, strips of cloth, or weatherproof marking
tape fastened to trees.
 
Allowances should be made for occasional turnouts to provide
space for passing or parking vehicles.   Any curves or switchbacks
should be of sufficient radius to be negotiated easily by the
largest vehicles likely to use the road.   As construction progresses,
a series of grade stakes or pegs are placed along the center
line of the road.  Two more or less parallel series of slope
stakes or pegs are then placed to mark the sides of the road.  See
Section III, Tools and Equipment, for more information about
maintaining grade and slope.
 
Measurment of Gradients
 
The steepness of a hill is usually expressed as the ratio between
the height climbed and the horizontal distance covered.   For
example, you are climbing a hill and walk forward 100 meters.  You
find then that you are 10 meters higher than when you began
moving.  This means that for each 10 meters you have moved forward,
you have also moved one meter upward.   In that case, we say
that the hill you are climbing has a slope of 1 in 10.
 
The main point that a road builder must always remember is that a
roadway should not be built with a slope steeper than 1 in 10.
Once in a great while, it may be necessary f or a road to be as
steep as 1 in 7 f or a very few meters.   This is an exceptional
case, and a steeper gradient would make the entire road unusable.
It is best never to accept a trace road plan showing a gradient
greater that 1 in 10.
 
You can convert a gradient expressed in degrees into a gradient
expressed as a proportion by using the following formula, in
which 60 is a constant:
 
   gradient as a proportion =            60
                               angle of gradient in degrees
 
For example, suppose that we have a gradient of 5[degrees].  We use the
formula to find out how to express this gradient as a proportion:
 
   gradient as a proportion = 60
                               5
                            = 12           gradient = 1 in 12
 
The same formula can be reversed to give us the gradient in
degrees when we know the gradient as a proportion:
                                            60
   angle of gradient in degrees =  -----------------------
                                   gradient as a proportion
 
Remember that the gradient of a road should not be steeper than 1
in 10.  That means that it should not be steeper than 6[degrees].
 
III. TOOLS AND EQUIPMENT
 
Tools for Finding the Grade
 
Equipment for building low-cost roads can very simple.   Bulldozers
and other large machinery may be nice, but they are costly to
operate and difficult to keep in repair without access to a
skilled mechanic and expensive spare parts.   It is important,
however, that the basic equipment be used to maintain the proper
grade and slope.  The most basic of these tools can be built by a
reasonably skilled carpenter.
 
The Grading Stick
 
A grading stick can be used to establish a gradient of not more
than 1 in 10.  A grading stick is about five feet long with 6-inch
bracket attached to one end so that the stick is ten times
as long as the bracket.  The slope that runs from the end of the
stick to the bottom of the bracket is a gradient of 1 in 10.
 
The grading stick is used for placing the grade stakes or pegs so
that the gradient is not steeper than 1 in 10.   The bracket of
the grading stick is placed on the peg that is further down the
slope; the end of the stick is placed on the peg that is further
up.  A spirit level is then laid on the grading stick.  The peg
can now be raised or lowered until the stick is level.   When it
is, you know that the gradient is exactly 1 in 10.
 
The Abney Level
 
The Abney level is a more complicated and accurate instrument
than the grading stick for finding the steepness of a gradient. <see figure 1>

ulr1x5.gif (353x353)


 
The Abney level is made up of three parts:   (1) A tube about six
inches long, with an eyepiece at one end and at the other end a
thin wire that horizontally divides the opening; (2) An arm
mounted above the tube, which can be moved along a scale calibrated
in degrees; (3) A small spirit level, coupled to the arm.
This level is reflected in a mirror set inside the tube.  In the
eyepiece you can see through the tube to the land beyond, which
appears cut horizontally by the thin wire.   You see the small
mirror to the right of this.   If you move the spirit level slowly,
you can see the reflection of the level's bubble as it crosses
the mirror.
 
The Abney level is best used along with a target and stick.  The
target consists of a piece of wood a foot square mounted at the
top of a wooden upright about 4 feet high.   The top half of the
square is painted white and the bottom half black.   The stick is
an ordinary piece of timber cut so that its height is exactly the
height of the point when the white half of the target adjoins the
black half.
 
The level is placed on the stick.   The target is taken to the
place where the gradient needs to be determined.   To use the
level you look through the eyepiece and adjust the wire until it
is exactly in line with the center of the target.   You then move
the spirit level until the bubble comes in line with the center
of the target.  The angle in degrees can then be read off the
calibrated scale.
 
It is much quicker to use an Abney level than a grading stick to
find a trace up a hillside, because with a grading stick, pegs
have to be put in and checked at five-foot intervals.   With the
Abney level, the surveyor can walk along a likely trace and
simply check, when the ground seems to be rising too steeply,
that the slope is not greater than 1 in 10 (i.e., that the angle
of incline is not greater than 6[degrees]).
 
Boning Rods
 
Boning rods are used to set the pegs that mark the center of the
road, and ensure that the pegs lie in the same plane.   The surface
of a road or bush path built without the help of boning rods has
many small dips and bumps, reflecting the shape of the ground
under the road.  Boning rods help assure that the surface of the
road will be level. <see figure 2>

ulr2x6.gif (317x317)


 
Boning rods are made of ordinary timber one inch thick.   They
always come in sets of three.   All three boning rods in a set must
be identical.  For this reason, if one of the rods wears down or
breaks, it must immediately be discarded and a new rod made to
replace it.  A boning rod is T-shaped; the height of the upright
of the T is 48 inches, and the length of the crosspiece is 36
inches.  The two arms are at right angles to each other, and must
be fastened together securely with three screwnails.   To use the
boning rods, you put them on the first two pegs and then sight
along the rods to place the third rod correctly.   If the crosspiece
of the third boning rod sticks up above the level of the
nearer two, then you must drive the peg on which it stands further
down.  If, on the other hand, the third crosspiece cannot be
seen, the peg is too low and must be made higher.   When you have
adjusted all three pegs in this manner, so that they are all in
line, the person carrying each rod moves forward so that the
next peg can be boned in (adjusted to the same level) in the same
way the others were.
 
 
The overseer of a road-building project has to decide where the
road will change levels.  In flat country, it may be possible for
the road to remain at the same level for distances of about 40
yards, but in hilly country the level may need to be adjusted as
often as every five yards.  Unless major obstacles like swamps and
mountains are unavoidable, you will probably want to select a
roadway that does not require adjustments in level of more than
three feet.  It is also desirable that the amount of earth that
needs to be excavated (or cut) be the same as the amount of earth
that needs to be used as fill.
 
Camber Rods
 
Camber rods are used to find the side to side slope, or camber,
of the road.  Like boning rods, camber rods are made of one-inch
timber.  They are usually eight feet long and have a bracket
attached to one end of the rod, at a right angle to the rod.  The
bracket, which is attached to the rod by three screwnails, protrudes
three inches below the rest of the rod.   Camber rods are
usually used in pairs, in conjunction with a spirit level. <see figure 3>

ulr3x7.gif (285x285)


 
The pegs marking the center line of the road are "boned in" using
the boning rods.  Behind the crew that bones in these center pegs
is a second crew that uses the camber rods to lay out the carriage-way
of the road.  The camber rod is put on the center peg,
with the long rod at right angles to the center of the road,
facing so that the bracket is on the outside.   The bracket is then
rested on a peg that will mark the edge of the roadway.   That peg
is driven into the ground until the spirit level shows the camber
rod has become level.
 
The three essential things to remember are:
 
1. The bracket always goes on the outside.   (there is one
 
The three essential things to remember are:
 
1.  The bracket always goes on the outside.  (there is one
    exception, which is explained on the next page.)
 
2.  The camber rod must always be at right angles to the center
    line of the road.
 
3.  The center peg must never be altered.  Only the outside peg,
    or camber peg, may be adjusted to make the rod level.  Once
    the camber peg on one side of the road has been adjusted,
    then the rod should be used to adjust the peg on the other
    side.
 
At this point, what you have is a line of pegs running down the
center of the road and, parallel to this line of center pegs, two
lines of camber pegs, one on either side of the road.   The camber
pegs are three inches lower than the center pegs, so that the
sides of the road will be lower than the center.   This slope is
called the camber.  It allows water to flow off the surface of
the road into ditches running along the sides of the road.  On a
gravel or dirt road, a crown of 1/2 to 3/4 inch per foot (measured
both ways from the center line) is adequate.
 
The camber pegs are joined with a string.   Then the crew making
the road can set to work.  First, they need to cut and fill around
the pegs.  Then they tamp or level the ground by moving a board
(or anything else with a straight edge) between the pegs.  They
dig a ditch on either side of the road, just outside the camber
pegs.  The slope of the sides of each ditch should be about 1:4 (1
meter of rise for every 4 meters of run), to prevent erosion.
Earth removed in digging these ditches can be used to build up
the camber.
 
The one exception to the rule that the bracket of the camber rod
always goes on the camber peg occurs when a road curves so that
its surface needs to be banked.   If, for example, a road curves
sharply to the left, a vehicle coming around the curve tends to
skid toward the right-hand ditch.   To help prevent this, the
right-hand half of the carriageway is built up higher than its
center.  To bank the road in this manner, the camber rod is used
in the normal way to set the camber on the inside (the left side
in our example) of the curve.   To set the opposite camber peg,
the bracket is put on the center peg, with the flat end of the
rod on the outside peg.  The result is that the outside peg is
higher than the center peg, and the center peg is in turn higher
than the inside one.  This is the only exception to the rule that
the bracket always goes on the camber peg.   And even in this
exception, the bracket goes on the center peg only when the peg
on the outside of the curve is being set.
 
MISCELLANEOUS EQUIPMENT
 
Several pieces of equipment should be mentioned in passing because
they are so basic; hoes and machetes, headpans, wheelbarrows,
and measuring tapes.
 
The Headpan
 
A headpan is a large pan, similar in shape to a dish pan.  Workers
carry it on their heads to transport earth or other loose materials.
It has the advantage of being simple and durable, and
usable even over rough terrain.   When the terrain is smooth, a
headpan is a relatively inefficient carrying device, since it
takes about 40 headpans of sand or earth to make up a cubic yard.
 
The Wheelbarrow
 
Under most conditions, and especially over long distances, a
wheelbarrow is a more efficient carrying device than a headpan
because of its greater capacity.   A wheelbarrow can hold about
seven times what a headpan can, but does require some maintenance.
The wheel axle needs to be oiled and the tire needs to be
pumped to the proper pressure on a rubber-tired wheelbarrow.
Without correct maintenance, the wheelbarrow is likely to break
down.
 
The Measuring Tape
 
A measuring tape is made of flexible metal or of linen cloth,
usually between 50 and 100 inches long.   The linen is preferred to
the metal because it costs less and lasts longer.   It is necessary
to clean and lightly oil the metal kind from time to time; otherwise
it will rust.
 
IV. DRAINAGE AND SLOPE STABILIZATION
 
A very experienced engineer was once asked, "What are the most
difficult problems encountered in road construction?" He
answered, "Water, water, and water."
 
Heavy rains can trigger floods, washouts, and landslides.  Smaller
amounts of water can turn roads into puddles, ruts, and quagmires.
Provisions must be made for adequate drainage if roads and
trails are to remain in serviceable condition.   In places where
floods are an annual occurrence, it may be necessary to build
bridges to keep the roads and trails usable year-round.   In rainy
areas and places with high ground water, ditches and road-shaping
are needed to carry the water away from the road or trail surface.
Too much water makes fine-grained soils soft and unable to
support traffic.  Too little water makes soils lose strength:  dry
fine-grained material is either blown away or pushed to the sides
by traffic.
 
Where the slope is near zero percent, the best way to handle
water is to build up the trail or road area with earth, so that
it is higher than the surrounding area.   In this case, every so
often there needs to be a means for water to get from one side of
the raised roadway to the other.   Culverts, bridges, or fords can
serve this purpose.  A culvert is a conduit or pipe under a road
or structure that permits the passage of traffic over water.  A
ford is a point where a road can cross a stream or river because
there is little or no water there much of the year, and because
the underlying soils can bear the weight of traffic.
 
A seep spring, or high water table will cause soft spots in a
road.  To solve this problem, you must remove the wet material
and replace it with a suitable drainage structure.   One way to do
this is to remove the wet material and leave a trench sloping
from the inside downward toward the outside of the road.  Fill
the trench with rock, starting with coarse rock at the bottom
and progressing to fine rock as you move upward.   The top of this
filling should come to within a foot of the finished grade.  Then
cover this porous material with a suitable base material, well
compacted.
 
On hilly or mountainous ground, the road or trail should have
some grade built into its longitudinal axis.   If the road has a
ditch, the water collecting in the ditch will need to pass over
or under the road.  Water should not be allowed to run down a
ditch or along the surface of a road or trail for any distance
that allows the water to pick up speed.   The steeper the grade,
the faster the water travels.   The faster the water travels, the
more capacity it has to carry soil and erode the surface of the
ditch or road.  Water must be removed more frequently as the grade
gets steeper.
 
CULVERTS
 
One of the most common methods of drainage is the installation of
culverts.  Culverts can be used to divert the flow of water in a
natural stream, or they can be used to help control run off water
that accumulates in the ditches.   Culverts can be made of lumber,
logs, concrete, steel, aluminum, or clay.   You should be sure
that the material you choose makes the culvert as durable and
easy to install as possible, and that it will be able to support
the loads that the road will be carrying.   If a metal or concrete
culvert is going to be carrying acid water, it should be lined
with vitrified clay or asphalt.
 
Stream Culverts
 
If you can, install the culvert in the natural drainage channel
and on the same grade as the stream. The inlet for a culvert
should be at or below the level of the stream bed, not above it.
Avoid filling under a culvert to bring it up to grade. Lay the
culvert on solid ground and pack the earth firmly at least halfway
up the side of the pipe so that water will not leak around
it. The culvert needs adequate cover: a minimum of one foot, or
half of the diameter of the culvert, whichever is greater. If it
is not possible to cover the culvert adequately, then you should
install two smaller culverts or a pipe arch. The cover needs to
be compacted to keep the road from settling. If there is a
problem with erosion at the inlet end of the culvert, then you
need to install a headwall. It can be made of such materials as
logs, concrete, or hand-placed riprap.
 
A culvert is usually made to run along a 2 to 4 percent grade so
that it will not become clogged. You can use an Abney level to
check the grade. The flow velocity of the water that runs through
the culvert should be greater than 2.5 feet per second to prevent
sedimentation but less than 8 feet per second to prevent scouring.
Generally speaking, a 2 percent grade will give you water
velocities within this range. The outlet end of the culvert
should be at or below the toe of the fill, and there should be an
apron of rock for the outflow to spill onto.
 
When there is no time to make an exact calculation, you can make
a hasty estimate of the cross-sectional area needed for a culvert
by doubling the channel area. This gives you just a rough approximation,
since it does not take into account the shape, size,
or slope of the area, or the surface vegetation, soil conditions,
or rainfall intensity. YOu can make a more exact calculation of
the cross-sectional area needed for a culvert by adding the
widths of the ditch at the top (a) and at the bottom (b), and
then multiplying them by its height (H):
 
                                    (a+b) H
 
The result should be roughly equal to double the cross-sectional
area of the channel.
 
Relief Culverts
 
There are two kinds of relief culverts:   ditch-relief culverts
and open-top culverts.
 
Ditch-relief Culverts. Ditch relief culverts are put in to move
water under the road before it acquires enough volume and force
to cause erosion to the ditch. The culverts should be spaced 200
to 300 feet apart on an 8 to 10 percent grade and about 500 feet
apart on a 5-percent grade. There will be local variations in
these figures depending on the width of the road, the type of
soil, and the amount of rainfall. Ditch-relief culverts should
cross the road at an angle of about 30 degrees (culvert outlet
downgrade about half the road width) to provide good entrance
conditions on steep slopes.
 
Open-top Culverts. Open-top culverts are used to remove water
from the surface of the road. The initial cost is low, but this
kind of culvert is hard to keep clean, must be installed and
bedded with care, and may break up under heavy traffic. These
culverts should be installed every 300-800 feet on roads with 2-5
percent grades and 200-300 feet where the grade is 6-10 percent.
 
DIPS AND WATER BARS
 
Dips and water bars are structures that help keep water from
accumulating on the roadways.
 
As shown in Figure 4, dips--often called sags--are built at low

ulr4x12.gif (243x486)


points in the road grade, where water seeks the lowest spot and
runs off the road. Dips must be constructed with exactness: their
length and depth must be adequate to provide drainage, yet not so
excessive as to endanger traffic. Side drainage must be provided
so that the dips do not become ponds that hold water on the
roadway. Note that dips are not designed to handle constantly
running water.
 
Water bars can be made of rocks, tree trunks, or compacted soil.
(Soil is not normally used because it erodes too easily.) About
two-thirds or three-fourths of the rock or tree trunk is buried
in the ground, leaving 2 to 4 inches exposed above the surface.
The water bar should lie at a 20 to 45 degree angle from the
perpendicular of the road or trail. Water runs along the bar to
its lowest point, where it runs off the side of the road. Figure 5

ulr5x13.gif (587x587)


shows how a water bar redirects the flow of water.
 
DITCHES
 
There are two common kinds of ditches:   trapezoidal ditches and
v-shaped ditches. The trapezoidal ditch is more difficult to
construct and maintain, but has a greater capacity than does a v-shaped
ditch of the same depth. The minimum size of trapezoidal
ditch that is practical to construct is 1-1/2 feet deep by 2 feet
wide at the bottom. A special ditcher is required if a trapezoidal
ditch is to be built by machine.
 
Whatever the soil type, heavy rain is likely to cause erosion in
any ditch with a grade of over 4 percent. If the road is expected
to be used for a short time only, the deepening of the ditch
through erosion may not be a problem. But if the road is supposed
to last, this erosion must be controlled, one way to do so is to
line the ditch with stone or other riprap material. Any ditch
with a grade of more than 10 percent should be paved.
 
Check dams may be put into the ditch at intervals to change a
single rush of water into a series of gentle flows. Their height
and spacing are chosen to produce the desired slope, usually one
of below 4 percent.
 
The spillway of a check dam must have a definite weir or notch-type
outlet. The bottom of the notch is the determining point
for calculating the grade. The bottom and sides of the dam should
extend 6 inches into the ditch line. The spillway needs to be
protected with rock riprap. The side of the dam that faces upstream
also needs to be protected from scouring. The check dam
can be made of concrete, steel, rocks, logs, sandbags, or earth
(earth should be used only if it is well protected from scouring).
 
TYPES OF ROAD SECTIONS
 
Five typical road sections and their uses are profiled below.
Both steepness of the slope and the conditions of the terrain
(e.g., whether the ground is dry or swampy) are factors that
determine which of the sections must be built at any given point
during road construction to permit good cross-drainage. For
example, locations on the side of a hill permit good cross-drainage.
They also have the advantage of involving a minimum of earth
moving since what is excavated can be used as fill. When slopes
exceed 60 to 70 percent in grade, this advantage is lost because
the roadbed must be placed in solid material, so all of the
excavated material becomes waste.
 
Turnpike Section. A turnpike section (Figure 6) is built on

ulr6x14.gif (270x540)


relatively flat ground with less than 10 percent slope, for
example, in swampy areas. It is designed to raise the ground
above the water table to prevent the road from being flooded. To
make a turnpike section, earth is extracted, or "borrowed" from
a ditch and used to create a fill on top of the original ground.
 
Fill Section. Fill Sections (Figure 7) are built on ground with

ulr7x14.gif (300x600)


slopes of up to about 50 to 60 percent. Where slopes are greater
than 60 percent, a fill section is used in drainage, raising the
ground above the streambed to allow water to pass underneath the
fill at ground level. To make a fill section, earth is taken
from another section of road (or from another area altogether)
and placed on top of the existing ground.
 
Through-cut Section. A through-cut section (Figure 8) is most

ulr8x15.gif (486x486)


often used when the road or trail goes through a ridge that has a
slope of less than 35 percent. This type of section involves
cutting earth from the ground. This earth then needs either to be
moved to another area where it will be used as fill or disposed
of altogether.
 
Self-Balanced Section. A self-balanced section (Figure 9) is

ulr9x15.gif (486x486)


built on slopes of between 10 and 60 percent. Building a self-balanced
section requires that the amount of earth cut out of the
hillside be equal to the amount used to construct the fill portion
of the road.
 
 
Full-bench Section. As shown in Figure 10, a full-bench section

ulr10x16.gif (486x486)


is built on slopes of 60 percent or greater. The term full-bench
refers to the flat bottom that is produced when the ground is cut
away to create the surface of the road. The material that is cut
is either hauled off to an area needing fill, or it is disposed
of over the roadside. Material that is disposed of over the edge
of the road is not stable and is not meant to support traffic.
 
MATERIALS AND SURFACING
 
Soil and rock are the basic materials for constructing roads and
trails. Sometimes all that needs to be done to make these materials
usable is to remove the vegetation from their surface. It
is also necessary to remove soil that is high in organic matter,
since it cannot adequately support the weight of traffic. The
rockier the soil is, the firmer the road will usually be and the
more support it will be able to provide. But rocky soil has the
disadvantage of making the surface of the road rougher. This can
often be resolved by spreading a layer of rocky soil to provide
support, and then covering the rocky layer with a 2- to 4-inch-thick
layer of sand-clay mixture to provide a smooth surface.
Usually, the soils are then shaped and compacted to provide for
drainage.
 
Generally speaking, the road that you are building must have a
surface that can both shed water and carry the expected loads. If
you are constructing an all-weather road, you must find surfacing
materials that will bear up under the full range of weather
conditions. It is not always easy to find surfacing materials
that meet these needs. Information on what materials are available
in your area can be obtained from your local highway district.
 
Crushed stone, stream gravel, and tuff are among the many different
materials that can be used for surfacing a road. The
materials you choose should be tough and lasting. It is possible
to upgrade a poor base material such as clay by mixing it with
rock or stream gravel, and adding a stabilizing agent like calcium
chloride or sodium chloride. You then compact the mixture to
get a dense, dust-free surface. If the road is going to carry a
large volume of heavy loads like lumber or coal, it may be economical
to pave it with asphalt to avoid long periods of shutdown
due to wet weather.
 
When the road is finished, short grass should be allowed to grow
around the ditches. A carriageway of 12 feet only should be kept
clear of grass. However, any culvert that crosses the road should
be about twice as long as the road width so that there is room
for two vehicles to pass each other at that point.
 
V. MAINTENANCE
 
Maintenance is required to keep roads and trails properly drained
and fit for travel. Maintenance costs can be kept to a minimum
in two ways:  through good initial construction, and through
proper, timely repair.
 
PERIODIC GRADING
 
Periodic grading of the road surface is necessary to fill in
wheel ruts and to reshape the road. This is done with a motor- or
tractor-drawn grader, a bulldozer, a rubber-tired skidder, or
a road drag. (A road drag is a platform weighted down with stones
and pulled behind a truck or tractor.
 
The purpose of grading is to restore the crown and to smooth the
surface of the road. Be sure to maintain the slope of the crown
1/2 inch to 3/4 inch per foot, so that storm runoff can be shed.
Shaping should be done at the end of the rainy season, after the
heavy moisture is gone but before the road has become hard and
dry. In the following months, routine smoothing should be done
after a rain that has moistened the road but not made it slippery
with mud.
 
DRAINAGE REPAIR
 
All ditches, culverts, water bars, and bridges must be kept clean
and in good repair. Particular attention should be given to
removing debris from culvert inlets, and to removing slides,
rocks, and other materials that have slipped off the banks.
 
When routine maintenance of ditches is being done, it is important
not to undercut the backslope. This will cause sloughing
into the ditch, and bring about washout and bank erosion.
 
DUST CONTROL
 
Excessively dusty roads cause hazardous driving conditions,
increase equipment maintenance costs, decrease the life of equipment,
and deteriorate road surfaces through losses in surface
material. Salts such as calcium chloride and sodium chloride are
the least expensive and most effective materials for controlling
dust. After shaping the road at the end of the rainy season,
while the ground is still moist, apply one pound per square yard
of road surface; during the dry season, apply one-half pound per
square yard.
 
EROSION CONTROL
 
Roads not used for long periods must be protected from erosion.
Drainage structures must be kept clean. Ditches and landings
should be planted with grasses and other vegetation.
 
                           GLOSSARY OF TERMS
 
Bar (water bar) - A barrier placed in the road to divert water
off the surface and over the edge.
 
Borrow - Soil or rock material removed (borrowed) from one area
to be used in another area.
 
Cross slope - The slope of the terrain.
 
Culvert - A conduit under a road or trail to allow the passage of
water.
 
Cut - The area excavated during construction of a road or trail.
 
Dip - A low point in a road or trail grade.
 
Ditch - A low point in the excavated portion of the cross-section,
intended for water flow.
 
Fill - The area where excavated material is placed during
construction.
 
Ford - A point in a stream or river where the water is shallow or
nonexistant during much of the year, and where the underlying
soils will support traffic.
 
Grade - The slope of the road or trail along its longitudinal
axis.
 
Slope - The unit of vertical distance per unit of horizontal
distance.
 
Waste - Excavated material that cannot be used in a stable fill.
 
                             BIBLIOGRAPHY
 
Armco Drainage and Metal Products. Handbook of Drainage and
Construction Products. Middletown, Ohio: Armco, [date].
 
Booth, E.D., and Woolverton, D.N. CARE Manual of Feeder Road
Construction. Freetown, Sierra Leone: CARE, 1977. This book
assumes an engineer is available.
 
Dalton, J.C. Maintenance of County and Rural Roads. Engineering
Experimental Bulletin 7. Moscow, Idaho: Idaho University, 1950.
 
de Veen, J.J. The Rural Access Roads Programme: Appropriate
Technology in Kenya. Geneva, Switzerland: International
Labour Office, 1980. Paperback.
 
Edmonds, G.A., and Howe, J.D.F.G. Roads and Resources: Appropriate
Technology in Road construction in Developing Countries.
London: Intermediate Technology Development Group, 1980. Paperback.
 
International Labour Office. Guide to Tools and Equipment for
Labour-Based Road Construction. Geneva, Switzerland: International
Labour Office, 1981. Paperback.
 
Jackson, Ian. Handbook of Fundamentals of Low-Cost Road Construction.
Awgu, Nigeria: Community Development Training Center, 1955.
 
Weigle, Weldon K. Designing Coal-Haul Roads for Good Drainage.
Berea, Kentucky: U.S. Forest Service, Experimental Station, 1960.
This is an excellent reference for farm-to-market roads when no
engineer is available.
 
                     SOURCES OF INFORMATION AND HELP
 
Most countries have a department of transportation or highways.
Within the department there are often sections that deal with
rural transportation and are good first contacts. If there is no
such department, or if it does not seem willing to help, try
similar departments in other countries where the same language is
spoken.
 
It may be difficult to find people who are interested in assisting
you on small self-help projects. Do not increase the project
size just to obtain help. Remember what the users want.
 
American Association of State Highway
 and Transportation Officials
444 North Capitol Street, N.W.
Suite 225
Washington, D.C. 20001 USA
 
American Society of Civil Engineers
345 East 47th Street
New York, New York 10017 USA
 
Louis Berger International, Inc.
100 Halstead Street
East Orange, New Jersey 07019 USA
 
Brazilian Road Research Institute
Ipr/Dner Rod Pres. Dutra
KM 163 Cep 21240
Rio de Janiero, Brazil
 
Brookings Institution
1775 Massachusetts Avenue, N.W.
Washington, D.C. 20036 USA
 
Cornell University
Local Roads Program
218 Riley-Robb Hall
Ithaca, New York 14853 USA
 
Henry Grace & Partners
Garthcliff, South Ridge
St. George Hill
Weybridge, Surrey ENGLAND KT130NF
 
International Road Federation
525 School Street, S.W.
Washington, D.C. 20024 USA
 
National Association of County Engineers
326 Pike Road
Ottumwa, Iowa 52501 USA
 
National Feeder Road Fund
Federation Nacional de Cafeteros de Colombia
Avenida Jimeng 7-65
Bogota, Colombia 281 8964
 
National Institute for Transportation
  and Road Research
P.O. Box 395
Pretoria
South Africa
 
ND LEA/Ministry of Public Works
P.O. Box 152 KBYT
Kebayoran Baru
Jakarta, Selatan, INDONESIA
 
Royal Institute of Technology
Department of Highway Engineering
Brinellvagen 34, Stockholm S 100 44
SWEDEN
 
Secondary Road Engineering
Federal Highway Administration
400 Seventh Street, S.W.
Washington, D.C. USA
 
Transporation Engineering
U.S.D.A. - Forest Service
P.O. Box 2417
Washington, D.C. 20013 USA
 
Transportation Research Board
2101 Constitution Avenue, N.W.
Washington, D.C. 20418 USA
 
U.K. Transport and Road Research Laboratory
Crowthorne, Berkshire
ENGLAND RGL 6AU
 
U.S. Forest Service
Experimental Station
Berea, Kentucky USA
 
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