Sec.5 - Road & Drainage Design Standards
5.1 Plan Preparation
- Road design shall conform to the current AASHTO guidelines, applicable MDOT design methodology, and WCRC requirements described herein.
- Road and Drainage Plans shall contain all the information necessary for constructing the project. The importance of general uniformity in plan documents is emphasized.
- Road and Drainage Plans shall be submitted on 24" X 36" sheets and 11" X 17" half-size sheets.
- English units of measure shall be used exclusively.
5.1.2 Survey & Drafting Methods
The Preliminary Plat shall be based upon the Michigan Coordinate System of 1983 using the current National Geodetic Survey adjustment on the date of the submittal with three points of reference, two section corners and one property corner. A statement by the Professional Surveyor as to how coordinates were developed and the datum and any adjustments used 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 WCRC, shall be established in each development and shown on the plans.; Each phase 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.
- All plans shall be generated using a computer aided drafting system.
Plan Sheets – At a minimum, Road & Drainage Plans shall include all of the following plan sheets and related information:
- Title Sheet signed and sealed by a Professional Engineer.
- Topographic and Boundary Survey Sheet signed and sealed by a Professional Surveyor
- Overall Layout Plan: Proposed road center line alignments shall be tied to two section corners and show bearings and distances.
- Overall Utility Plan
- Stormwater Management Plan
- Grading & Soil Erosion/Sedimentation Control Plan
- Municipal Utility Plan/Profile Sheet
- Road and Drainage Plan/Profile Sheet
- Intersection Detail Plan
- Typical Cross Section & Miscellaneous Detail Plan
- Landscape Plan
- Construction Traffic Control Plan
- Permanent Traffic Control Devices Plan
5.1.4 The plan must meet the current requirements of WCWRC Rules and Guidelines.
5.1.5 All road and drainage construction shall be illustrated using plan/profile drawings.
5.1.6 Plan/Profile sheets shall be drawn scales not less than one inch = 50 feet horizontal and one inch = 5 feet vertical.
5.1.7 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-ways.
5.1.8 Plan view of each road shall show the centerline, stations, curve data, edge of pavement, back of curb, sidewalk, sidewalk ramps, and sidewalk landings.
5.1.9 The profile of each proposed road shall be shown directly below the plan view and shall contain the following:
- Profile of existing centerline.
- Proposed centerline.
- Percent of grade and vertical curve data.
- Existing and proposed grades at the right-of-way.
- Left & right proposed top of curb.
- Centerline and any proposed/existing ditch of existing county road(s) adjacent to proposed subdivision with proper outlet thereto.
- Numerical elevations of the existing ground and proposed roads at each half station (50 ft.)
5.1.10 Plan/Profile sheets shall show sizes, gauge, lengths, material, end treatments and locations of all cross road culverts.
5.1.11 Plan/Profile sheets shall show location, size and cover type of proposed catch basins, inlets and cleanout points for underground drainage systems.
5.1.12 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.
5.1.13 Road & Drainage Plans shall include all WCRC and MDOT Standard Plans and Special Details that are being utilized in the development.
5.2 Grades & Earthwork
5.2.1 Vertical alignment of the road surface establishes the profile grade line 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, 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.
5.2.2 A vertical curve shall be required when the algebraic difference in road grade is greater than or equal to one. A vertical curve shall be required for any change in grade when the design speed is greater than or equal to 30 mph.
5.2.3 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.
5.2.4 Vertical curves shall have minimum length of 100 feet and shall be designed with K values that meet or exceed the minimums listed in Table 1.
5.2.5 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 super-elevated primary or local roads.
5.2.6 Typical Cross Sections
- The minimum requirements for road widths and pavement structures will vary, and will be based on traffic volumes and public need. Residential roads will have a minimum width of 11 foot lanes, up to a maximum of 14-foot lanes. Corporate Park/Commercial roads will have a minimum width of 14-foot lanes. WCRC typical cross sections are provided in the Appendix.
- All roadways shall include MDOT F4 24-inch concrete curb and gutter. No open ditch drainage systems will be allowed for new public roadways.
- Non-standard pavement section designs may be considered provided their structural strengths are equivalent or greater than those contained in the Appendix. The Design Engineer may submit complete pavement designs for WCRC consideration using the AASHTO Pavement Design methodology for either flexible or rigid pavements.
5.2.7 The transverse slope (crown) on all pavements shall be 2%.
5.2.8 Slopes behind curbs shall be 4% (½ 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.
5.2.9 Continuous subgrade underdrains shall be provided on all roadways. Subgrade underdrains shall be at least 6” diameter and conform to the current MDOT Standard Plan Series R-80. Positive outlets for underdrains, such as catch basins, shall be spaced no more than 300 feet apart.
5.2.10 All proposed road approaches at existing roadways shall utilize MDOT B2 Modified 30-inch curb and gutter through the internal spring point.
5.2.11 Berms will not be allowed within the road right-of-way.
5.2.12 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.
- Log of Soil Borings: A detailed soils investigation shall be conducted and submitted to WCRC to determine the suitability of proposed roadbed material. The soils investigation report shall be signed and sealed by a 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 shall 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 WCRC.
5.2.14 Soil Erosion & Sedimentation Control
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 prevent sedimentation from adversely 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 175 feet. A horizontal curve table shall be provided on the sheet showing where the point of intersection appears, chord length of the intersecting alignments, point of curvature, point of tangency, point of intersection, external angle, degree of curve, and length of the curve.
Curves shall be sufficiently long to avoid the appearance of an abrupt change (“kink”) in the alignment of the road.
Back-to-back reverse curves are generally discouraged. However, if they must 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. See the Appendix for cul-de-sac details.
- The radii of corners at intersections shall be 35 feet to the back of curb.
- 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 PRPA.
5.3.3 Sight Distance – Both stopping sight distance and intersection sight distance must be evaluated for all road designs. 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. Sufficient sight distances must be ensured based on current WCRC PRPA.
The stormwater management system shall be in accordance with WCWRC Rules and Guidelines and constructed in accordance with MDOT Standard Specifications for Construction. All storm sewers constructed within the right-of-way shall be MDOT class E sewers.
All utilities shall be located in accordance with alignment requirements in the PRPA. All franchise utilities shall be located in an easement outside the right-of-way when available. 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.
5.6.1 The Developer shall incorporate Complete Streets Best Design Practices where applicable.
5.6.2 Sidewalks shall conform to applicable MDOT standard plans and specifications and shall adhere to all ADA requirements.
5.6.3 Multi-use or shared use pathways may require special considerations such as additional right-of-way or a separate easement beyond the road right-of-way, depending upon the required road cross section and other geometric features.
5.6.4 Streetlights (luminaires) placed within the right-of-way shall be owned and maintained by a public utility recognized by WCRC in accordance with the PRPA.
- 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 where they 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.
- For purposes of placement, a streetlight 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-ways of subdivision developments with the exception of those areas illustrated 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. Deciduous trees are allowed within cul-de-sac 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.
5.6.6 Sign PlansPlans 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. Prior to acceptance of roads 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.
5.6.7 Mailboxes shall be located in the right-of-way pursuant to the current WCRC Procedures for the Installation of Mailboxes and Newspaper Delivery Boxes along County Roads.
5.6.8 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, fences, buildings, landscape lighting, and privately owned utilities.
5.6.9 Residential Driveways
- A WCRC permit is required in accordance with PRPA prior to driveway construction.
- Driveway approaches within the right-of-way shall not have a width greater than 20 feet nor a vertical profile exceeding +/- 6%.
- Proposed or existing driveways within the development shall be located no closer than 50 feet from the right-of-way of an intersecting road or outlot.
Procedures & Regulations for Developing Public Roads, effective August 6, 2014