Town of Cohasset, MA Article V Design Standards

§ 325-25 General requirements.

A. All lots shown on a definitive plan submitted to the Board for approval shall comply with the applicable zoning bylaws for the Town of Cohasset, Massachusetts, in force at the time of application.

B. Convenient maintenance of all proposed construction shall be a consideration.

C. Due regard shall be exercised in the design and during the construction process to ensure that drainage or any other activity above or below the surface of the ground is not allowed to contaminate any watercourse, body of water or groundwater.

D. Earth removal. The tentative or final approval of a definitive plan by the Board shall not be construed as authorizing the removal of material from the premises, even though in connection with the construction of streets shown on the plan. All earth removal within subdivisions shall be in accordance with the regulations governing earth removal contained in the Zoning Bylaw for the Town of Cohasset, Massachusetts.[1]

[1] Editor's Note: See Ch. 300, Zoning, Art. 11, Regulations Governing Earth Removal.

E. The subdivision shall harmonize and conform with plans for Cohasset as adopted by the Planning Board and/or Board of Selectmen.

F. Protection of natural features. Due regard shall be shown for all natural features, such as large trees, watercourses, scenic points, historic spots and similar community assets, to preserve, promote and enhance the natural beauties and amenities of the Town and add value to the subdivision.

G. Open spaces. Before approval of a plan, the Board may in proper cases require the plan to show a park or parks suitably located for playground or recreation purposes or for providing light and air in accordance with the Subdivision Control Law. The park or parks shall not be unreasonable in area in relation to the land being subdivided and to the prospective uses of such land. Final disposition of such areas shall be in accordance with the Subdivision Control Law.

H. In the case of a definitive plan showing the connection of ways within the subdivision over a private way to a public way, approval of the definitive plan shall be denied unless the applicant has sufficient rights in the private way to enable the applicant to bring the private way into conformance with the requirements of these rules and regulations, or as waived pursuant to MGL c. 41, § 81R. The definitive plan shall show such private way, together with other applicable systems.

I. Obligations of applicant to make improvements. Where the physical condition or width of a public way from which a subdivision has its access is considered by the Board to be inadequate to carry the traffic expected to be generated by such subdivision, the Board may require the applicant to dedicate a strip of land for the purpose of widening the abutting public way to a width at least commensurate with that required within the subdivision and/or to make physical improvements to and within such public way to the same standards required within the subdivision. Any such dedication of land for the purpose of way and any such work performed within such public way shall be made only with permission of the governmental agency having jurisdiction over such way, and all costs of any such widening or construction shall be borne by the applicant.

J. Wherever possible, subdivision design shall incorporate principles of sustainable development, energy-conscious design and the Cohasset Open Space and Recreation Plan.

§ 325-26 Streets.

A. Streets in the subdivision shall be coordinated with each other and with the existing street system in a manner satisfactory to the Board, with due regard to the purpose of the Subdivision Control Law and these rules and regulations.

(1) Provision satisfactory to the Board shall be made for the proper extension of streets, or for access to adjoining property which is not yet subdivided.

(2) Reserve strips prohibiting access to streets or adjoining property shall not be permitted, except where, in the opinion of the Board, such strips shall be in the public interest.

(3) Insofar as practical, streets shall be located a suitable distance from existing dwellings of abutters and/or landscaping shall be provided as required by the Board to buffer noise and other impacts from proposed streets.

B. Alignment.

(1) The street system shall conform to the approved preliminary plan, if any.

(2) Streets shall be continuous, of uniform width and in alignment with existing streets.

(3) Long straight roadway sections should be avoided in minor streets.

(4) Street jogs with center-line offsets of less than 125 feet shall be avoided.

(5) Proposed names of all streets in the subdivision shall be subject to approval by the Assessor, Police Chief, Fire Chief and Emergency Notification Coordinator (utilizing street naming Form 7 contained in these rules and regulations) as indicated by the signature of each. In the event that a proposed name is not approved, the Assessor will recommend or assign a replacement name.

(6) Connections with uncompleted extensions of adjacent ways shall be accomplished. When adjoining property is not subdivided, if required by the Board, ways shall be laid out to the perimeter of the subdivision shown on the plan. Easements for temporary turnarounds outside of the way lines shall be provided. Such easements shall terminate in the manner provided in MGL c. 41, § 81Q. Except by permission of the Board, such turnarounds shall be constructed to the same standards as permanent turnarounds. Frontage for lots abutting a temporary turnaround shall be computed along the way lines. Due provision shall be made for demolition of temporary turnaround construction not needed or authorized after extension of the way.

(7) The minimum center-line radii of streets shall be 150 feet. Greater radii may be required for streets which are principal streets in the Board's opinion. All streets shall be designed to permit safe vehicular travel. Adequate clear sight distance shall be provided at all road intersections.

(a) Clear sight distance at the intersection of a subdivision access road and an existing way shall be defined by a clear sight triangle at the intersection. Two sides of the triangle shall coincide with the center lines of the access road and the existing way respectively. The third side of the triangle, measured from the center line of the access road at a point 30 feet from the center line of the existing way, shall be identified as the clear sight distance. Depending on maximum design approach speed, along the existing way, minimum clear sight distance shall be as follows:

	Maximum Design Approach Speed (miles per hour)	Clear Sight Distance (feet)
	45	350
	35	250
	25	150

(b) Measurements of the clear sight distance shall be based on a line of sight of a level 5 1/2 feet above road surfaces at each end of the clear sight distance.

(c) Inside the clear sight triangle, no vision-obstructing object shall be permitted within a vertical distance of 3 1/2 feet from the line of sight.

(d) Similar sight distance methodology shall be used in the design of interior subdivision intersections.

(8) As a minimum requirement for adequate sight distance at intersections, right-of-way lines shall be rounded by tangent arcs with minimum radii of 30 feet. To ensure adequate sight and to accommodate turning of emergency vehicles, the Board may require greater radii.

(9) No street shall intersect any other street at less than a seventy-five-degree angle.

(10) Intersections shall be separated from other road intersections on the same or opposite side by a minimum of 200 feet. This requirement shall apply not only to separation of road intersections within a subdivision, but also to separation of any subdivision access road from any other intersection at any existing way.

C. Width.

(1) In areas zoned for residences, street layouts shall not be less than 40 feet in width. Streets which, in the opinion of the Board, may be used for through or heavy local traffic must be at least 50 feet in width.

(2) In areas zoned for industry, the minimum street widths shall be not less than 50 feet.

D. Grade. Except as noted below, grades of all streets shall not be less than 1%, nor more than 6%. Where the 6% requirement would result in considerable injury to the aesthetic value of the site due to extensive cut and/or fill or tree removal, the Board may waive the 6% requirement provided such waiver is consistent with safety determinants, including the distance from an intersection, the number of housing units served, the type of street, the length of the steeper graded portion of the street, the horizontal alignment and street curvature. At all intersections, grades of streets shall not exceed 2% within a distance of 50 feet from the beginning of the intersection. (The beginning of the intersection as referred to herein shall be defined as the point at which the edges of the travel lanes intersect.) At intersections of two proposed streets, grades of streets shall not exceed 2% within 50 feet from the beginning of the intersection. Street grade at cul-de-sac turnarounds shall not exceed 3%. There shall be a vertical curve for any change in street grade. Vertical curves shall be designed considering drainage and sight distance impacts. Vertical curves shall not be designed with over 50 feet of the curve at a grade less than 0.5%.

E. Cross section. Streets shall be constructed in accordance with the standards as shown on the Typical Cross Sections for Street Layouts (see Figure 1 and Figure 2) and in accordance with these regulations.[1]

[1] Editor's Note: Figures 1 and 2 are included as attachments to this chapter.

F. Dead-end street.

(1) Dead-end streets shall not be longer than 1,500 feet as measured by street stationing.

(2) The paved area of temporary or permanent culs-de-sac shall have an outside radius not less than 50 feet. Cul-de-sac stationing shall loop around the cul-de-sac 20 feet or other approved distance off the street side line and rejoin the roadway stationing at the beginning of the cul-de-sac.

(3) Permanent culs-de-sac in residential zones shall have planting islands in their center with a radius of 15 feet.

§ 325-27 Utilities.

All utilities, except as otherwise specified, shall be placed underground at the time of initial construction in accordance with the following:

A. Storm drainage.

(1) A complete and adequate storm drainage system, designed to the satisfaction of the Board, shall be so laid out and of sufficient size as to permit unimpeded flow of all natural waterways, to provide adequate drainage of all surface and subsurface water of the street system so that water does not accumulate thereon, to intercept stormwater runoff from the adjoining land and to eliminate undesirable or unnatural accumulation of water on any portion of the subdivision or surrounding property.

(a) The design shall provide for minimum subsequent maintenance. Design of drainage shall be such as not to increase off-site flooding. Analysis of drainage and flooding impacts off site for the two-, ten-, and one-hundred-year storm shall be submitted as evidence of conformance with these regulations.

(b) The design of all drainage systems for street drainage within the subdivision, including catch basin grates, shall be in accordance with calculations, based upon the storm frequency and rainfall intensity data provided in Figure 6,[1] utilizing the rational method. Other methods with proven predictive capabilities (e.g., those based on TR 55) may be approved. Said approval shall be solely at the discretion of the Board.

[1] Editor's Note: Figure 6 is included as an attachment to this chapter.

(c) Design of detention ponds shall be based on the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55, by the Engineering Division, Natural Resources Conservation Service, United States Department of Agriculture, with the exception that rainfall intensity curves used for the design of all drainage conveyance and storage systems shall be based on Atlas of Precipitation Extremes for the Northeastern United States and Southeastern Canada, Northeast Regional Climate Center Research Series Publication No. RR 93-5, September 1993, or the most recent version. The rational method shall not be used to generate rainfall hydrographs used in the design of detention ponds or similar water storage structures. Calculations shall be based upon the following storm frequencies:

[1] Ten years for street drains.

[2] Twenty-five years for culverts draining areas of less than 50 acres.

[3] Fifty years for culverts and other drains draining areas of 50 acres or more.

(d) Notwithstanding the above requirements, all components of the drainage system shall be designed so that the drainage system functions as intended.

(2) In certain instances, the Board may require that the design of a drainage system be based upon storms of greater frequency.

(3) Calculations shall be made using recent topographic maps for the entire contributing drainage area, including those areas outside the subdivision. Copies of all drainage calculations and Town topographic maps or other more recent or accurate maps (where available) illustrating the entire drainage area and showing all subarea boundaries utilized in said calculations shall be submitted as part of the definitive plan submission.

(4) The storm drain system shall include catch basins, manholes, culverts, drain lines, headwalls, flared ends and such other items as may be required to complete the system to the satisfaction of the Board.

(a) Catch basins shall be located in pairs, one on each side of the roadway, at all low points or sag curves in the roadway, at intervals of not more than 400 feet on continuous grades of the roadway, and at or near the corners of the roadway at intersecting streets. Each catch basin shall connect directly to a manhole.

(b) Manholes shall be located at all changes in direction, either horizontally or vertically, of a drain line or at the intersection of two or more drain lines, or so located that no drain line of a length greater than 400 feet would exist without a manhole.

(c) Culverts shall be designed on the assumption that the entire drainage area is built up to that intensity and in the manner which the applicable section(s) of the Zoning Bylaw would allow. The calculations (or a copy thereof) necessary to determine the size of any culvert which carries a brook, stream, river, or other natural waterway shall be submitted to the Board for review. All culverts shall have a concrete headwall at each end, and any culvert over 36 inches in diameter shall include at the upstream end additional protection, as approved by the Board, for roadway side slopes. Headwalls shall be constructed in accordance with MassDOT Standard Details.

(d) In areas where the finished grade of the roadway is less than four feet above the water table or in other areas where, in the opinion of the Board, the subgrade must be drained, a system of subdrains acceptable to the Board may be required.

(e) All drains shall be a minimum of 12 inches in diameter and shall be laid on a slope of not less than 0.5%. The minimum design velocity shall be three feet per second and the maximum design velocity shall be 10 feet per second. All outfalls shall extend to a natural waterway. Provision shall be made for the disposal of surface water intercepted or collected by the system in such manner that no flow is conducted over Town ways, or over land of others unless a drainage easement therefor is obtained or unless such flow is essentially the same quantity as previously existed in the same location.

[1] Stormwater shall be directed to enter the most suitable natural watercourse or be properly connected to any existing drains in adjacent streets or easements which may exist. Where no adequate drainage system exists, or where it is inadequate in the opinion of the Planning Board, it shall be the responsibility of the applicant to extend the system outside the subdivision in a manner specified or approved by the Board to properly dispose of all the drainage from the proposed subdivision.

[2] Where adjacent land is not subdivided, provision shall be made for the extension of the system by continuing appropriate drains to the boundary of the subdivision at such size and grade as will allow their proper projection.

(f) A concrete headwall or concrete flared end section designed in accordance with MassDOT Standard Details shall be provided at the outfall end of all drains. Scour protection shall be provided at all headwalls or flared ends.

(g) Where applicable, tidal effects shall be taken into account in the design of the storm drainage system.

(h) Private drains may be installed to connect to the public stormwater drainage system. Design and installation shall be by agreement with the Town. A plan of the private drain shall be furnished to the Board for approval.

(i) Private drains shall be so located on the lot and so constructed such that no seepage from any on-lot sewerage system shall enter the private drain.

(j) Culverts or drains proposed to have grates at their inlets shall be designed with their inlet capacity reduced 25%.

(k) Culvert and drain design shall be based on a Manning roughness coefficient "n" = 0.013.

(l) Grates shall be provided on the inlet and outlet ends of all pipes over 15 inches in diameter.

(m) At the request of the Board a drainage design to eliminate or remove any other water or waters within the subdivision limits and not designated as roadway or subsurface water, and which is otherwise not taken care of, shall be drawn in a manner approved by the Board.

(n) Drainage design for street drainage shall be such that pipes flow without surcharge for the storm frequency and intensity required.

B. Public water supply.

(1) No subdivision of land shall be approved by the Planning Board unless all lots therein are provided with water by connection to the Town of Cohasset's public water supply system. Water mains and their appurtenances must be installed in accordance with the Rules and Regulations of the Cohasset Water Department and approved by the Department. Size of water mains shall be as recommended by the Cohasset Water Department.

(2) Public water mains shall be not less than eight inches in diameter unless a smaller diameter is approved by the Cohasset Water Department. There shall be a hydrant within 500 feet of any existing or potentially existing building.

(3) Hydrants shall be located as shown on the typical cross section for the applicable street.

C. Sewer system.

(1) All public sewer facilities design shall conform to the applicable current rules and regulations of the Sewer Commission and Guides for the Design of Wastewater Treatment Works by the Technical Advisory Board of the New England Interstate Water Pollution Control Commission.

(2) Sewer design shall be reviewed by the Sewer Commission and the Planning Board. Subdivisions within 500 feet of an existing sewer may be required to connect into the existing sewer.

(3) On-site sewage disposal systems shall be designed in accordance with all applicable local, state and federal regulations.

D. Other public utilities.

(1) Electricity, communication, gas and cable television shall be installed in all subdivisions. They shall be installed underground in the location shown on the appropriate typical cross section contained herein and shall be installed in accordance with the utility company having jurisdiction.

(2) If a utility mentioned above is not proposed for the site, written evidence from the specific utility company involved that the utility is not available to serve the site shall be submitted.

E. Easements.

(1) Easements for storm drains, sanitary sewers or water mains across lots, or centered on rear or side lot lines, shall be provided for the Town where necessary and shall be at least 20 feet wide. No easement shall be permitted across land of others unless an agreement in proper form is obtained permitting such easement.

(2) No building or on-lot sewerage system shall be erected within an easement.

(3) Where a subdivision is traversed by a watercourse, drainageway, channel or stream, the Board may require that there by conveyed to the Town without cost a stormwater easement of adequate width depending upon the width of the stream. This easement shall conform substantially to the lines of such watercourse, drainageway, channel or stream and shall provide for construction, maintenance or other necessary purposes in relation thereto.