Sec.5 - Road & Drainage Design Standards
5.1 Plan Preparation
- Road design shall conform to the current AASHTO Policy On Geometric Design of Highways and Streets, applicable MDOT design methodology, and the WCRC requirements described herein.
- Road and Drainage Plans shall contain all the information necessary for constructing the subdivision project. Although innovation and creativity are encouraged in the preparation of plans, the importance of general uniformity is emphasized.
- Road and Drainage Plans shall be submitted on 24" X 36" sheets.
- English units of measure shall be used exclusively.
5.1.2 Survey & Drafting Methods
- Beginning July 1, 2005 Road and Drainage Plans shall be based on a ground survey based on the current adjustment of the Michigan Coordinate System of 1983 (MCS 83, Act 9, P.A. of 1964, as amended). A statement by the Professional Surveyor as to how coordinates were developed shall appear on the plans.
- All elevations shall be based on the North American Vertical Datum of 1988 (NAVD 88). A permanent benchmark, conforming to standards adopted by the WCRC, shall be established in each development and shown on the plans. All phases of a development shall have at least one benchmark, and all developments larger than 20 acres shall have at least two benchmarks. A benchmark detail can be found in the Appendix (Figure 35).
- All plans shall be generated using an automated drafting system.
5.1.3 Plan Sheets At a minimum, Road and Drainage Plans shall include all of the following plan sheets and related information:
- Title Sheet
- Topographic and Boundary Survey Sheet (by licensed Professional Surveyor)
- Overall Layout Plan
- Overall Utility Plan
- Grading & Soil Erosion/Sedimentation Control Plan
- Municipal Utility Plan/Profile Sheet
Road & Drainage Plan/Profile Sheet
- All road and drainage construction shall be illustrated using plan/profile drawings with the existing and proposed road centerline profile, including all proposed vertical curve data and proposed ditch and storm sewer illustrated directly below the plan view.
- Plan/Profile sheets should be drawn to a scale no less than one inch to 50 feet horizontal and one inch to 5 feet vertical.
- Plan/Profile sheets shall show the location, size, material type and elevation of all existing and proposed drainage systems and underground utilities within existing and proposed road right-of-way.
- Plan view of each road shall show the centerline, stations, and curve data. Centerline profile shall be shown directly below the plan view.
- Profile of existing centerline.
- Percent of grade and vertical curve data.
- Existing and proposed centerline.
- Right ditch and right-of-way.
- Left ditch and right-of-way.
- Centerline, ditch and proposed ditch of county road(s) adjacent to proposed subdivision with proper outlet thereto.
- Percent of grade of proposed centerline and independent ditches.
- Numerical elevations of the existing and proposed centerline shown at each half station (50 ft.)
- Plan/Profile sheets shall show sizes, gauge, lengths, material, end treatments and locations of all crossroad culverts.
- Plan/Profile sheets shall show location, size and cover type of proposed catch basins, inlets and clean out points for underground drainage systems.
- Plan/Profile sheets shall show plan and profile of all proposed drainage system elements outside of the road right-of-way that are to be connected to existing or proposed road drainage facilities.
- Intersection Detail Plan
- Landscape Plan
- Construction Traffic Control Plan
- Permanent Traffic Control Devices Plan
- Stormwater Management Plan
Standard Plans, Special Details & Notes Sheet
- Standard Plans and Special Details - Show details for all applicable trenches, catch basins, inlets, manholes, etc. This can be completed by reference to current MDOT Standard Plans and Special Details.
5.2 Grades & Earthwork
5.2.1 Vertical Alignment
- General: Vertical alignment establishes the profile gradeline of a proposed road construction project. Establishing the vertical alignment is based on many factors, including but not limited to terrain, existing conditions, soils, drainage, and coordination with the horizontal alignment, location of bridges, culverts, intersections, design speed, and earthwork balance.
- The minimum grade on any road shall be 0.5 percent.
- The maximum grade on any road shall be 6.0 percent.
Vertical Curves (Crest and Sag)
- A vertical curve shall be required when the algebraic difference in road grade is greater than or equal to two. A vertical curve shall be required for any change in grade when the design speed is greater than or equal to 30 mph.
- Stopping sight distance is the principal controlling factor for the design of both crest and sag vertical curves. Stopping sight distance shall meet or exceed the stopping sight distance values illustrated in Table 1.
- Vertical curves shall have minimum length of 100 feet and be designed with K values that meet or exceed the minimums listed in Table 1.
- Where intersecting roads meet existing primary or local roads, the grade of the proposed intersecting road shall match the transverse slope (crown) of the existing primary or local road as extended to the right-of-way line. Special consideration must be given to intersecting roads with existing superelevated primary or local roads.
5.2.2 Typical Cross Sections
Typical Cross Sections
- The minimum requirements for road widths and pavement structures are shown in Table 2. The table is divided into sections for HMA and PCC pavement cross sections based on subdivision development type and lot density. Each section is further divided according to commonly used road classifications. WCRC typical cross sections are provided in the Appendix.
- Non-standard pavement section designs may be considered by the WCRC provided their structural strengths are equivalent or greater than those contained in Table 2 are. The Design Engineer may submit complete pavement designs for WCRC consideration using the AASHTO Pavement Design methodology for either flexible or rigid pavements.
- The road widths and pavement structure requirements shown in Table 2 are only intended to represent the minimum requirements established by the Board.
- The transverse slope (crown) on all pavements shall be 2%. The cross slope of all shoulders shall be 4% or 1/2 inch per foot.
- Roadside slopes shall be 1V:4H or flatter. Slopes behind curbs shall be 4% or 1/2 inch per foot through cut and fill sections from the back of curb to the hinge point. The hinge point shall be located five feet from the back of curb. Slopes from the hinge point to existing ground shall be 1V:4H or flatter. In cut sections, storm sewer, including a catch basin with beehive casting, shall be placed at the hinge point at all low points.
- Berms will not be allowed within the road right-of-way.
- Designs that necessitate guardrail installation are discouraged. Any design that utilizes guardrail will require a written justification. Further, a full design meeting current MDOT standards will be required. The Developer shall correct resulting construction that would create a need for guardrail installation. The cost of corrective action shall be the responsibility of the Developer.
Table 2: Typical Pavement Cross-Sections
- Log of Soil Borings: A detailed soils investigation shall be conducted and submitted to the WCRC to determine the suitability of the proposed roadbed material. The soils investigation report shall be prepared, signed and sealed by a licensed, professional engineer. Soil boring locations shall be shown on the plans at the true and accurate locations where they were performed. All borings must occur within the influence of the proposed roadway. Soil boring logs shall be superimposed on the plan/profile sheets and include geotechnical information including: date the boring was taken, who performed the boring, the elevation of the water table (or "dry"), soil classification using the Unified Soil Classification System (USCS) or the AASHTO System, and subgrade modulus or California Bearing Ratio (CBR).
- All trees, stumps, roots and brush shall be removed from the AASHTO clear zone within the road right-of-way, unless otherwise permitted by the WCRC.
5.2.4 Soil erosion and sedimentation controls shall be designed in accordance with current MDOT standard plans, special details, and standard specifications for construction to minimize erosion and to control sedimentation from affecting water resources and adjacent properties.
5.3 Alignment & Geometrics
5.3.1 Horizontal Alignment
- The centerline of construction shall coincide with the centerline of the right-of-way. Section line and quarter section line roads shall be centered on the respective survey lines.
- The minimum centerline radius for horizontal curves shall be 230 feet. A horizontal curve table shall be provided on the sheet where the point of intersection appears, specifying point of curvature, point of tangency, point of intersection, external angle, degree of curve, and length of the curve.
- Curves should be sufficiently long for small deflection angles to avoid the appearance of an abrupt change in alignment ("kink") in the road
- Back-to-back reverse curves are generally discouraged. However, if they are to be used, the curves shall have the same radius and length of curve.
- It is desirable that all intersecting roads meet at right angles, but in no case shall the intersecting angle be more than a 10-degree difference from 90 degrees. Corner radii of skewed intersections shall be increased as necessary to conform to AASHTO guidelines.
- Adjacent intersections on the same side of an intersected road within a subdivision shall be spaced no less than 125 feet apart, as measured between the points of intersection.
- Intersecting roads on opposite sides of an intersected road within a subdivision shall be in direct opposition (share a common point of intersection) or be offset no less than 255 feet, as measured between the points of intersection.
- All dead end roads shall be provided with a paved circular turnaround.
- The radius of corners at intersections shall be 35 feet to the edge of pavement for rural cross sections and to the back of curb for urban cross sections.
- Each approach at an intersection shall provide a minimum 100-foot tangent along the centerline, measured from the center of the intersection. A variance may be granted for an approach located on the outside of a curve, if sight distance per AASHTO is assured.
- Boulevards for an entrance may only be considered where a "T" intersection is created, and where development directly across from the proposed entrance is unlikely. Where boulevards are permissible, they shall be curbed with a width no less than 20 feet back to back. Boulevard sections shall be no more than 300 feet in length, and shall not extend beyond the edge of the intersecting road or its auxiliary lane. Sufficient taper of the roadway width must be provided adjacent to the interior end of the boulevard, per MDOT requirements. Breaks between boulevards are not permissible. In no case shall a boulevard exist within the road right-of-way of the existing road.
- Proposed subdivision roads intersecting with existing primary or local roads shall be designed and constructed in accordance with the current WCRC Procedures and Regulations For Permit Activities.
5.3.3 Sight DistanceBoth stopping sight distance and intersection sight distance must be evaluated for all road design. In general, the Design Engineer can use graphical methods to check sight distance on horizontal curves and at intersections. Both the horizontal and vertical alignments must be considered when designing for sight distance. Stopping sight distance is defined as the minimum sight distance available on a road that is sufficiently long enough to enable a vehicle traveling at or near the design speed to stop before reaching an object in its path. Intersection sight distance is the distance required for a driver of a vehicle on a minor road or driveway approach to safely cross or enter the major roadway from a stopped position. Sufficient sight distances must be ensured based on current AASHTO guidelines.
5.4 Plan Preparation
- Drainage design shall be in accordance with the current MDOT Drainage Manual.
- The Design Engineer shall submit all design calculations to the WCRC with the Road & Drainage Plans.
- All culverts, bridges, storm sewer and appurtenances shall be designed pursuant to AASHTO design standards for HS-20 or greater loading on all roads.
- The Design Engineer shall provide an acceptable system of drainage to enable property owners to drain sump pump outlets, roof drains, and similar private drainage features. Connection of these private drainage features to WCRC right of way is prohibited.
5.4.2 Storm Sewer
- Drainage design for storm sewer and curb and gutter sections shall be based on the ten percent chance (10-year) storm frequency. The effects of a 1 percent chance (100-year) storm shall be checked for possible harmful interference to adjacent properties.
- Enclosed drainage systems shall be designed for self-cleaning velocities.
- The design spread for surface drainage shall be no greater than one-half the driving lane.
- Proposed drainage structures and covers installed within the road right-of-way shall conform to current MDOT Standard Plans and Special Details.
Spacing of Structures shall conform to the following:
- Catch basins, inlets and culverts shall be placed so that all intersections and low points are properly drained. Additional or intermediate catch basins, inlets, or culverts may be required by the WCRC to facilitate proper drainage patterns, existing or proposed.
- Catch basins and inlets should be designed so that they align with side lot lines and avoid conflict with proposed driveway opening locations.
- Drainage structures shall be located at all changes in sewer alignment, size or grade. Storm sewers shall be located and aligned to best conform to the layout of existing facilities. In roads where no pattern has been established, storm sewers shall be located on the east or north side of the road.
- Drainage structure spacing and inlet capacity shall conform to MDOT specifications and shall prevent standing water on the roadway.
Construction of roadway storm sewer facilities shall conform to the following:
- Storm sewer installation within County road right-of-way shall conform to MDOT specifications. All storm sewer installation shall be inspected and certified by the Construction Engineer and shall be true to line and grade, and properly bedded and backfilled.
- Construction of drainage systems shall conform to the current MDOT Standard Specifications For Construction and the requirements described herein.
5.4.3 Roadside Ditches & Culverts
- Drainage design for roadside ditches and culverts shall be based on the ten percent chance (10-year) storm frequency. The effects of a 1 percent chance (100-year) storm shall be checked for possible harmful interference to adjacent properties.
- The high water elevation in all roadside ditches shall be at least one foot below the shoulder point (freeboard) and the maximum allowable water depth shall not exceed two feet.
- Ditches shall be designed and constructed on each side of the roadway in cut and fill sections. Ditches shall be a minimum of two feet (2’) in depth below the shoulder point, and deeper where necessary to place the minimum cover over culverts or to provide independent ditches with adequate flow characteristics.
- All ditches shall have an established growth of vegetation provided by topsoiling, seeding and mulching in accordance with MDOT specifications. The minimum roadside ditch grade shall be 1.0%. Ditch grades with slopes in excess of 4% shall be riprapped, paved or stabilized with applicable turf reinforcement mats.
- Roadside ditches shall be stabilized with vegetation and free of rills and sediment prior to acceptance by the Board.
- MDOT Class E culverts shall be used for all crossroad culverts. The minimum diameter of all crossroad culverts shall be eighteen inches (18”). Crossroad culverts shall be of sufficient length that the inlet and outlet inverts extend to the bottom of the ditch.
- Prefabricated flared end sections shall be used on all culverts.
- Materials and methods for installation of culverts shall conform to MDOT specifications.
- The minimum diameter of all driveway culverts shall be twelve inches (12”).
- Direct discharge of storm water (detained or undetained) to existing or proposed roadside ditches servicing the existing county road system shall not be permitted unless historic data show this condition existing prior to development.
5.4.4 Underdrain Continuous subgrade underdrains shall be provided on all curb and gutter cross sections. Subgrade underdrains shall be at least 6” diameter and conform to the current MDOT Standard Plan Series R-80. Positive outlets for underdrains shall be spaced no more than 300 feet apart.
5.5 Surfacing, Shoulders, and Curb & Gutter
Proposed urban road approaches at existing roadways shall utilize MDOT B2 curb and gutter through the internal spring point. Further information regarding roadway surfacing, shoulder, and curb and gutter is found in Table 2 and in the individual pavement cross sections located in the Appendix
5.6.1 All utilities shall be located in accordance with the following alignment requirements and the current WCRC publication, Procedures and Regulations For Permit Activities. All lot or house services shall be extended to the right-of-way line prior to subgrade approval. All public underground utilities shall be installed after the rough grading has been completed so that proper cover over the utilities can be determined and verified.
5.6.2 Overhead Utilities
- Utility poles placed within the public road right-of-way shall be owned and maintained by a public utility recognized by the WCRC. Private utilities shall not be placed in the public road right-of-way.
- Utility poles shall be located beyond the clear zone and in accordance with the current AASHTO Roadside Design Guide.
- Target positions to traffic flow should be avoided if possible. The number of utility poles should be kept to a practical minimum. Consideration should be given to utilizing joint-use construction where possible.
- Utility poles are not permitted in locations that would obstruct sight distances.
- The placement of utility poles includes all related appurtenances.
- All lateral distances are measured from the traffic side of the utility pole to the edge of pavement or back of curb if applicable.
5.6.3 Underground Utilities
- All proposed underground utilities shall be installed within the proposed road right-of-way prior to subgrade approval.
- It is recommended that all open trench underground utility installation and road construction work be accomplished in one construction season and final road surfacing (top course) be placed during a subsequent construction season.
5.6.4 Utility Alignment
- Storm sewers – shall be located and aligned to best conform to the layout of existing facilities. In roads where no pattern has been established, storm sewers shall be located on the east or north side of the road between the back of curb and right-of-way line.
- Sanitary sewers – shall be located and aligned to best conform to the layout of existing facilities. In roads where no pattern has been established, sanitary sewers shall be located on the west or south side of the road between the back of curb and right-of-way line.
- Water mains – shall be located and aligned to best conform to the layout of existing facilities. In roads where no pattern has been established, water mains shall be located on the east or north side of the road, between the back of curb or edge of pavement and the right-of-way line.
- Gas mains – shall be looped throughout the subdivision and are typically located in a private utility easement adjacent to the road right-of-way. Installation of service leads under the roadway shall be avoided.
- Other utilities – shall be located within an easement adjacent to the right-of-way.
5.7.1 Sidewalks Sidewalks, when called for on the plans, shall conform to MDOT specifications and Americans with Disabilities Act requirements, or the local governing body’s standards, as approved by the WCRC.
5.7.2 Multi-use pathways - Dependent upon the required road cross section and other geometric features, proposed multi-use paths may require special consideration including additional right-of-way or a separate easement beyond the road right-of-way.
- Streetlights (luminaires) placed within the public road right-of-way shall be owned and maintained by a public utility recognized by the WCRC. Private utilities shall not be placed in the public road right-of-way.
- Streetlight supports shall be located at a uniform offset at least 5 feet behind the back of curb.
- Streetlight supports are not permitted in locations that would obstruct sight distances.
- Target positions to traffic flow should be avoided if possible. The number of streetlight supports should be kept to a practical minimum.
- The placement of streetlights includes all related appurtenances.
- All streetlight supports shall be equipped with breakaway devices, typically classified as frangible bases, slip bases, or frangible couplings, which meet the current requirements of the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.
- Trees are allowed in the road right-of-way of subdivision developments with the exception of those areas illustrated in Figures 32 and 33 located in the Appendix. Such trees shall be located outside the clear zone as defined by the current AASHTO Roadside Design Guide.
- Non-deciduous plantings are prohibited within the right-of-way. One deciduous tree is permitted per cul-de-sac island. Deciduous trees are allowed within boulevard islands when sufficient sight distances are ensured.
- All trees must be shown on the landscaping plan.
- Landscaping berms will not be allowed within the road right-of-way.
5.7.5 Sign Plans - Plans shall illustrate all required signs and locations pursuant to the current MMUTCD and shall include a quantity table identifying the MMUTCD codes and sign dimensions. Plans shall include Figure 31 located in the Appendix. The Developer shall be responsible for erecting and maintaining interim traffic control devices (stop signs, road names, etc.) pursuant to the approved Road & Drainage Plan prior to acceptance of roads.
5.7.6 Mailboxes shall be located in the right-of-way pursuant to the current Road Commission policy Procedures for the Installation of Mailboxes and Newspaper Delivery Boxes along County Roads.
5.7.7 Encroachments are strictly prohibited in the road right-of-way. Examples of encroachments include, but are not limited to, plantings in the right-of-way other than exceptions granted herein, rocks, berms, headwalls, private signs, flagpoles, irrigation systems, sump pump and footing drains, fences, buildings, landscape lighting, or privately owned utilities.