(a) Generally. An all-weather, paved-surface street with curb and gutter and proper drainage facilities is required. The roadway surface should conform to the typical cross-section of abutting curbed, platted streets, except where a higher type of surface is required.
(b) Street design requirements.
(1) Two-lane sections.
A. The width of the street shall be a minimum of 27 feet from back of curb to back of curb. (See Figures 1, 2 and 3, following the text of this chapter.)
B. For a curb and gutter cross-section, the crown shall be three inches minimum.
C. The sight distance over a crest shall be a minimum of 300 feet viewed from a point three feet, six inches above the surface of the pavement, with the object sighted being three feet, six inches above the surface of the pavement.
D. The maximum grade on any portion of a street shall not exceed 6% (a rise or fall of six feet in 100 feet). The minimum grade shall be 0.40% measured along the centerline of the street, except that on the circle area of a cul-de-sac, the developed minimum grade shall be 0.6%, measured along the outside edge of the cul-de-sac.
E. The minimum radii on platted street intersections shall be as follows:
1. State and federal highways: as approved by the MDOT;
2. Major local or primary roads: forty feet to the back of the curb;
3. Residential area streets: thirty feet to the back of the curb; and
4. Commercial and industrial platted streets: thirty-five feet to the back of the curb.
(2) Boulevard platted streets at intersections.
A. Pavement width on each side of the median divider shall be not less than 27 feet from back of curb to back of curb.
B. All medians shall be curbed in essentially the same manner and according to the same detail of curb and gutter used elsewhere throughout the development. High curbs, flagstone walls or similar medians will not be permitted.
C. The distance from the back of the curb to the street right-of-way line shall be not less than the minimum distance approved elsewhere in the plat, except on cul-de-sacs with approval from the city.
D. The median divider maximum length from end to end shall be 200 feet. The minimum length along the same dimensions shall be 100 feet.
E. Median dividers shall be not less than 12 feet nor more than 20 feet in width from back of curb to back of curb and shall be of uniform even width. Hour glass or other odd shaped medians shall not be permitted. Minimum radii at median ends shall be one-half of the uniform median width.
F. The material placed between the curbs, inside the median, may consist of sodded earth, limestone chips, brick or similar material approved by the city.
G. The only other items to be sanctioned within the limits of the median, until such time as the plat is approved, will be low growing shrubbery, a maximum of 18 inches in height.
H. The typical cross-section of the boulevard section, at its midpoint, showing the pavement crown and other pertinent information, shall be required as a part of the street and drainage plans.
(3) Cul-de-sacs. Cul-de-sac length should be limited to seven times the average lot width and in no case should a cul-de-sac exceed 1,200 feet in length. Special consideration may be given to longer cul-de-sacs under certain topographic conditions or other unusual situations.
(c) Drainage design requirements; underground storm sewers.
(1) All underground drainage used to drain the streets in a development must be approved by the city’s DPW. When requested, design data supporting the adequacy of the underground drainage system shall be furnished before approval of the plans. Storm sewer pipe shall be C76, 12-inch minimum diameter placed at a minimum 2.5 fps grade slope. Storm sewer design shall be at no less than a 25-year storm. The minimum initial time of concentration shall be 20 minutes. The run-off coefficient for single-family shall be 0.4, for multifamily 0.5, and for commercial-industrial 0.75. Adjustments of run-off factors must be approved by the city’s DPW prior to use.
(2) Where possible, the underground storm sewer of adequate diameter shall be laid with sufficient gradient to be self-cleaning. Catchbasins, when used, shall have minimum two-foot sumps. Structures may be two feet interior for less than four feet of depth. All structures exceeding four feet in depth must be at least four feet interior diameter.
(3) The proper type of pipe and bedding, complying with MDOT specifications, shall be used as necessary for good design. Granular material backfill must be used in trenches under all roadways and in all trenches, the inside edges of which are within three feet of the back of the curb. Backfill material shall be compacted to a minimum of 95% modified Proctor (ASTM Test T-99).
(4) Manholes (or other approved clean-out points) on underground drainage systems must be placed at maximum intervals of 400 feet.
(5) Manholes shall be built according to the MDOT Standard Plan with Cover A. Catchbasins shall be built according to the MDOT Standard Plan with the approved cover, unless otherwise approved by the city.
(6) Where applicable, an approved method must be used to drain the subbase or subgrade. The minimum size open joint drain tile used shall be six inches in diameter.
(7) Approaches to catchbasins or inlets behind the curbs shall be sodded or otherwise protected from erosion.
(8) On cul-de-sacs having circular turn-arounds, a catchbasin or inlet will be required in the gutter to drain the circular area, unless it can be positively determined by the city’s DPW that the gradients and the like, are sufficient to warrant omitting these structures (minimum pavement grade slope within the circle area of a cul-de-sac shall be 0.6%). If a planting island is created in such turn-arounds, a similar structure must be built in the island gutter or the island gutter must be built 0.4% higher than the outside radius gutter and the island shall have a slope-away gutter. Following construction, if these areas do not drain to the satisfaction of the city, the installation of the necessary drainage structures will be required before acceptance of the street.
(9) Soil erosion and sedimentation control measures shall be required.
(10) The proprietor shall provide an acceptable auxiliary system of underground drainage to enable lot owners to drain sump pump outlets, roof drains and similar private drainage into an approved storm sewer network. This sump pump system may be an approved solid wall PVC pipe a minimum of eight inches in diameter with standard structures for clean-outs.
(Res. passed 11-12-1986)