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| 5.8. Maintenance of Dirt and Gravel Roads
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Over 1.6 million miles of unpaved roads (53 percent of all roads) are unpaved. Many
of these roads will remain unpaved due to very low traffic volume and/or lack of
funds to adequately improve the subgrade and base before applying pavement layer(s).
In some countries, economic constraints mean gravel roads are the only type that
can be provided.
Dirt and gravel roads represent a very small percentage of roadways maintained by
state DOTs in almost all cases; counties and federal agencies manage the large majority
of the dirt and gravel roads in the United States. Nevertheless, a few state DOTs
have become very involved in managing dirt and gravel roads and have developed environmental
stewardship practices and partnerships that may be useful for other state DOTs.
General practices for pollution prevention from dirt and gravel roads include:
- Stabilize exposed soil areas to prevent soil from eroding during rain events.
This is particularly important on steep slopes.
- For roadside areas with exposed soils, the most cost-effective choice is to
vegetate the area, preferably with a mulch or binder that will hold the soils in
place while the vegetation is establishing. Native vegetation should be used if
possible.
- If vegetation cannot be established immediately, apply temporary erosion control
mats/blankets; a comma straw, or gravel as appropriate.
- If sediment is already eroded and mobilized in roadside areas, temporary controls
should be installed. These may include: sediment control fences, fabric-covered
triangular dikes, gravel-filled burlap bags, biobags, or hay bales staked in place.
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| 5.8.1 Partnerships
to Identify and Address the Most Pressing Erosion Problem Areas |
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The Pennsylvania Task Force on Dirt and Gravel Roads is a cooperative
effort between PennDOT and several other state and private agencies to improve the
environmental quality of Pennsylvania's streams and waterways. PennDOT started working
with Trout Unlimited in the early 1990s to mobilize volunteers to identify sedimentation
problem areas from eroding roads and shoulders and areas of adverse impacts to streams.
Initial efforts concentrated on Pennsylvania' protected watersheds, designated as
either High Quality (HQ) or Exceptional Value (EV), and including drinking water
reservoirs and cold water fisheries. Trout Unlimited's volunteer effort culminated
in the identification of over 900 sites, which became the basis for the Dirt and
Gravel Road Pollution Prevention Program. In 1999-2000, a statewide committee followed
up with a statewide inventory and assessment of all 17,000+ miles of Pennsylvania's
dirt and gravel road network. Conducted by County Conservation Districts, this effort
identified more than 9600 specific pollution sites impacting more than 3,000 miles
of roadway. All 9600+ worksites were mapped, rated (on a 12-step, 100 point scale)
and recorded in GIS program files. Top priority in the first three years was given
to pollution "trouble spots" identified in watersheds protected as "exceptional
value" and "high quality." As of 2000-01, a new allocation formula
was used to distribute funding to affected communities statewide, with verified
pollution sites on unpaved roads. Pennsylvania's 65 Conservation Districts administer
the program at the county level with annual allocations from the State Conservation
Commission. With the help of a local Quality Assurance Board (QAB), they:
- Work directly with applicants to develop plans for projects
- Assist with logistics of project work whenever possible
- Keep track of records of projects in their County using GIS system
- Develop a prioritization ranking incoming applications through the QAB
- Decide which project will be funded each year, through the QAB, and
- Conduct project inspections after site work is completed
To be eligible to apply for funding, an official form a municipality must attend
a free 2-day training on environmentally sensitive maintenance for unpaved roads
that explains basic environmental principles and introduces new techniques and ideas
in unpaved road maintenance. The Center for Dirt & Gravel Road Studies at Penn
State conducts "Environmentally Sensitive Maintenance," a 2-day course
that includes modules on drainage, road maintenance techniques, erosion prevention
& sediment control, bank stabilization, roadside vegetation management, and
grant procedures.
In assessing progress toward addressing priority erosion control areas statewide,
the program tracks:
- Drainage Outlets Stabilized (Sq Ft)
- Eroded Ditch Stabilized (Sq Ft)
- Road Bank Stabilized (Sq Ft)
- Stream Bank Stabilized (Sq Ft)
- Fabric Used (Sq Ft)
- Stream Culverts Replaced (#)
- Cross Pipes Added (#)
- Road Stabilized (Sq Ft)
- Vegetative Management (Sq Ft)
- Length of stream culverts replaced (Ft)
- Length of cross-pipes added/replaced (Ft)
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| 5.8.2 Tools
and Techniques for Erosion Reduction/Prevention |
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PennState's Dirt and Gravel Roads Center provides extensive resources and program
information for managing dirt and gravel roads. The Center provides an extensive
Dirt & Gravel Roads training program that is available upon request. Technical
bulletins available on-line include:
The Center's list of environmentally acceptable products
for petroleum emulsion dust suppressant, acrylic polymer dust suppressant, road
fill materials, soil amendments is also available on-line.
A variety of other technical resources are available from federal agencies, teams,
and other states in some instances. The Local Technology Assistance Program maintains
a listing which includes the following of potential interest to state DOTs: [N]
South Dakota's Gravel
Roads Maintenance and Design Manual is a comprehensive manual available in both
html and pdf
formats that addresses most issues that deal with gravel road maintenance. The practices
included in the manual are available via the links below:
Example 14 :
South Dakota DOT Gravel Roads Maintenance and Design Manual Sections
Section I: Routine
Maintenance and Rehabilitation
Understanding Road
Cross Section
Routine Shaping Principles
- Operating Speed
- Moldboard Angle
- Moldboard Pitch
- Motorgrader Stability
- Articulation
- Windrows
- Crown
- Road Shoulder
- High Shoulders ( Secondary Ditches )
- Causes of High Shoulders
- Recovering and Spreading on Roadway
- Breaking up Sod and Vegetation in Recovered Material
- Pulling and Covering
- Benefit of Mowing
- Gravel Road Rehabilitation
- Reshaping Surface and Shoulder
- Reshaping Entire Cross Section
- Erosion Control
- Areas of Concern
- Dealing with Corrugation
- Intersections
- Intersection with Paved Roads
- Bridge Approaches
- Superelevation in Curves
- Rail Crossings
- Driveways
- Cattle Guards
- Soft and Weak Subgrade
- Section II: Drainage
- Ditches
- Culverts and Bridges
- Underdrains
Section III: Surface
Gravel
- What is Good Gravel?
- Difference in Surface Gravel and Other Uses.
- Good Gradation
- Benefit of Crushing
- Recycled Asphalt
- The Benefit of Testing Aggregates
- Reasons for Testing
- Sampling
- Sieve Analysis
- Fines and Plasticity Index
- Reduced Blading and Maintenance Costs
- Process for Obtaining Good Gravel
- Establish Specifications
- Communicate with Suppliers
- Handling Gravel.
- Pit/Quarry Operations
- Loading from Stockpiles
- Roadway Preparation
- Calculating Quantity
- Hauling and Dumping
- Windrowing, Equalizing and Spreading
Section IV: Dust Control/Stabilization
- Types of Stabilizers
- Chlorides
- Resins
- Natural Clays
- Asphalts
- Soybean Oil
- Other Commercial Binders
- Benefits of Stabilization
- Reduced Dusting
- Reduced "Whip Off" of Aggregate
- Reduced Blade Maintenance
- Application Tips
- Need for Good Surface Gravel
- Road Preparation
- Applying the Product
- Optimum Moisture
- Test Sections
Section V: Innovations
- Changes in Gravel Maintenance
- Changing Conditions - Equipment, Trucks, Cars
- New Innovations
- Innovative Equipment and Methods
- Windrow Pulverizers
- New Cutting Edges
- Shouldering Disks
- Grader-Mounted Dozer Blade
- Grader-Mounted Roller.
- Rakes
- Other Tractor-Mounted Blading Devices
Summary
References
Appendix A : Gravel
Road Thickness Design Methods
Appendix B: Gradation
and P.I. Determination
Appendix C: Quantity
Calculations
Appendix D: When
To Pave a Gravel Road
Appendix E: Walk-around
Grader Inspection
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