A.
Location and alignment.
(1)
All streets in the subdivision shall be designed so that, in the judgement of the Planning Board, they will provide safe vehicular travel. Due consideration shall be given by the subdivider to the attractiveness of the street layout in order to obtain the maximum livability and amenity of the subdivision.
(2)
The proposed streets shall conform, so far as practicable, to the Master or Study Plan when adopted in whole or in part by the Planning Board.
(3)
Reserve strips prohibiting access to streets or adjoining property shall not be permitted, except where, in the judgment of the Planning Board, such strips shall be in the public interest.
(4)
Provisions satisfactory to the Planning Board shall be made for the proper projection of streets or for access to adjoining property which is not yet subdivided.
(5)
Street jogs with center-line offsets of less than 125 feet should be avoided.
(6)
The minimum center line radii of curved streets shall be 100 feet. Greater radii may be required for principal streets.
(7)
Streets shall be laid out so as to intersect as nearly as possible at right angles. No street shall intersect any other street at less than 60°.
(8)
Property lines at street intersections shall be rounded or cut back to provide for a curb radius of not less than 30 feet.
C.
Grade.
(1)
Grades of streets shall be not less than 0.5%. Grades shall not be more than 6.0% for principal streets nor more than 8.0% for secondary streets.
D.
Dead-end streets.
(1)
Dead-end streets shall not be longer than 500 feet unless, in the judgement of the Planning Board, a greater length is necessitated by topography or other local conditions.
(2)
Dead-end street shall be provided at the closed end with a turnaround having an outside roadway diameter of at least 100 feet and a property line diameter of at least 115 feet.
E.
Drainage.
(1)
Storm drains, culverts and related facilities shall be designed to permit the unimpeded flow of all natural watercourses, to ensure adequate drainage at all low points along streets, to control erosion and to intercept stormwater runoff at intervals reasonably related to the extent and grade of the area being drained; and to the maximum extent feasible, stormwater shall be recharged to the ground rather than piped off the premises. The rate of surface runoff from a site shall not be increased after construction.
(2)
Storm drains shall be based on a twenty-five-year frequency storm, and culverts shall be based on a fifty-year frequency storm, with consideration given to damage avoidance for a 100-year storm.
(3)
Design shall be based upon any of the following runoff volume calculation methods: Rational, Hydrograph, Stankowski, or computer software adaptation of these runoff value calculations, provided that their data and graphic printouts allow review and evaluation. Water velocities in pipes and gutters shall be between two feet per second and 10 feet per second, and not more than five feet per second on ground surfaces.
(4)
A catch-basin-to-manhole drain configuration shall be used. All drain pipes shall be at least 12 inches in diameter made of reinforced concrete conforming to Massachusetts DPW specifications for Class II pipe or such higher class as may be required by depth of cover, which shall be less than 24 inches nor more than 10 feet, subject to Planning Board review.
(5)
Catch basins will be required on both sides of the roadway on continuous grade at intervals of no more than 300 feet. Any catch basins and manholes used shall be at least six feet deep and four feet in diameter (inside measurements) with a thirty-inch or greater sump below the pipe invert, and shall be constructed of concrete blocks or precast concrete units Manhole covers and grates shall be placed so as to cause no hazard to bicycles. Manholes shall not be spaced more than 300 feet apart. Detention facilities will be required subject to the review of the Planning Board.
(6)
Proper connections shall be made with any existing drains in adjacent streets or easements which prove adequate to accommodate the drainage flow from the subdivision. In the absence of such facilities or inadequacy of the same, it will be the responsibility of the developer to extend drains from the subdivision as required to properly dispose of all drainage from said subdivision in a manner determined to be proper by the Board.
(7)
Lots shall be prepared and graded consistent with existing drainage patterns in and around the subdivision and in such a manner that development of the lot shall not cause detrimental drainage on another lot or on areas outside the subdivision. If provision is necessary to carry drainage to or across a lot, an easement of drainage right-of-way of minimum width of 20 feet and proper side slope shall be provided.