§ 3.5. Design standards for streets.

3.5.1

General. In order to provide for roads suitable in location, width, and improvement, and to coordinate roads so as to compose a convenient system and avoid undue hardships to adjoining properties, the following design standards for roads are hereby required and shall be planned for and provided by the developer, prior to the approval of the final plat. Road classifications may be indicated on the comprehensive plan, otherwise they shall be determined by the Greene County Board of Commissioners.

3.5.2

Classification of streets. Streets shall be classified into a street hierarchy system and street design standards shall be based on road function and projected average daily trips (ADT), calculated with trip generation rates published in the "Trip Generation Manual," 1998 Edition. Residential lots shall require ten trips per day per single-family lot and 16 trips per day per two-family lots. Street classes and their corresponding average daily trips (ADT) are:

Classification	Maximum	Maximum
Local street	25 dwelling units	250 ADT
Minor collector	250 dwelling units	2,500 ADT
Major collector	500 dwelling units	5,000 ADT
Arterial streets	N/A	5,000 ADT and more

 

3.5.3

Geometric design standards for streets. Geometric design standards for roads and streets shall be based on Table 3.5.3.

GEOMETRIC DESIGN STANDARDS FOR STREETS
TABLE 3.5.3

	Arterial	Major Collector	Minor Collector	Local
Average daily trips (ADT)	5,000 or more	4,999—2,500	2,499—250	249 or less
Minimum right-of-way	100 feet (64 feet with curb and gutter)	80 feet (64 feet with curb and gutter)	60 feet (50 feet with curb and gutter)	60 feet (50 feet with curb and gutter)
Minimum centerline grade	1.5%	1.5%	1.5%	1.5%
Maximum centerline grade:
Level	6%	7%	7%	7%
Rolling	7%	8%	10%	12%
Hilly	9%	10%	13%	15%
Minimum stopping sight distance	550 feet	450 feet	250 feet	150 feet
Design speed	55 MPH	45 MPH	35 MPH	25 MPH
Minimum curve radius at centerline	850 feet	500 feet	400 feet	250 feet
Maximum superelevation rate	6%	6%	6%	4%
Minimum tangent between reverse curves	300 feet	200 feet	100 feet	100 feet
Edge of pavement radius at intersections	30 feet	30 feet	25 feet	25 feet
Minimum shoulder width	8 feet	8 feet	8 feet	6 feet

 

Notes:

(1) Terrain classification shall be as follows:

Level—Cross slope range from 0% to 8%

Rolling—Cross slope range from greater than 8% to 15%

Hilly—Cross slope range from over 15%

(2) Where curb and gutter is not required, the shoulder shall slope away from the pavement at a slope of six percent. Where curb and gutter is required, the shoulder shall slope toward the curb at a slope of four percent.

(3) All shoulder widths are measured either from the edge of pavement or back of curb.

(4) No existing or proposed cut or fill slope shall [be] 3:1 within 11 feet of the roadway shoulder as specified above. Beyond said 11 feet, the slope is preferred to be 3:1, but may increase to a maximum of 2:1 until intersecting existing grade. All cut and fill must be confined to the right-of-way or slope easements.

3.5.4

Base and paving design. Base and paving design standard specifications shall be based on Table 3.5.4.

TABLE 3.5.4
MINIMUM BASE AND PAVEMENT DESIGN SPECIFICATIONS

	Arterial	Major Collector	Minor Collector	Local
Base width	25 feet	23 feet	23 feet	21 feet
Graded aggregate base thickness	8 inches	8 inches	6 inches	6 inches
Asphalt concrete base	6 inches	4 inches	N/A	N/A
Asphalt concrete binder	3 inches, type B	2 inches, type B	2 inches, type B	2 inches, type B
Asphalt concrete surface	1½ inches, type E	1½ inches, type E	1½ inches, type E	1¼ inches, type F
Triple surface treatment	N/A	N/A	N/A	Yes
Minimum pavement width	24 feet	22 feet	22 feet	20 feet

 

Notes:

(1) Pavement widths do not include curb and gutter.

(2) Pavement in tangent sections shall have a parabolic crown of at least one-eighth inch per foot.

(3) Curves shall contain no reverse super elevation with the exception of turnarounds, alleys, access drives, and local streets.

(4) Curb and gutter shall be Standard 9032B of the Georgia Department of Transportation or roll curbing.

(5) If the finished pavement on any street has a total thickness of less than four inches, the underlying base course shall be primed.

(6) On any paved street that does not have curb and gutter, the underlying base course shall be of a design thickness and compaction such that it extends to six inches outside the pavement edge.

3.5.5

Continuation of existing streets. Where feasible, existing streets shall be extended for access into the subdivision. Such extensions shall be continued at the same or greater width, but in no case shall be less than the required width.

3.5.6

Vertical curves.

1.

All transitions in profile grade, between successive vertical tangents having an algebraic difference greater than one percent, shall be by means of a parabolic curve.

2.

All changes in street profile grades having algebraic difference greater than one percent shall be connected by a parabolic curve having a minimum length (L) equal to the product of the algebraic difference between the grades in percent (A) and the design constant (K) assigned to the street according to its category (i.e., L=KA).

3.

Constant (K) values are shown in the Table 3.5.6 for minimum acceptable values.

TABLE 3.5.6
CONSTANT (K) VALUES FOR VERTICAL CURVES

Design Speed (mph)	K—Crest Curve	K—Sag Curves
15	3	10
20	7	17
25	12	26
30	19	37
35	29	49
40	44	64
45	61	79
>45	See GDOT standards	See GDOT standards

 

3.5.7

Clear sight distance at intersections. There shall be a minimum clear sight distance at intersections when measured from a height of six feet, as follows:

Arterial streets: 400 feet

Collector streets: 300 feet

Local streets (nonresidential): 250 feet

Local street (residential): 200 feet

Alleys: 150 feet

Where two or more streets of different classifications intersect, the sight distance requirement for the highest classification street shall be used.

Where any street intersection will involve slopes or existing vegetation inside any lot corner that would create a traffic hazard by reducing sight distance below specified minimums, the developer must cut such ground or vegetation (including trees) in connection with the grading of the public right-of-way to the extent deemed necessary to comply with the sight distance of these regulations.

3.5.8

Intersection design. Street intersections shall be as nearly at right angles as possible. No street intersection shall be at an angle of less than 60 degrees. For minor collector and arterial streets, street intersections must be separated from each other by at least 125 feet measured along the right-of-way line. For major collector and arterial streets, street intersections must be separated as defined in the "Georgia Department of Transportation Design Policy Manual" where feasible, but in no case be spaced less than 600 feet apart as measured between centerlines of said streets.

3.5.9

Culs-de-sac. All culs-de-sac shall meet street requirements for local streets (residential) except any cul-de-sac approved for a length greater than 1,200 feet or more than 25 dwelling units shall meet design criteria for a minor collector street.

3.5.10

Turnaround. Turnarounds shall be provided at the end of cul-de-sac or dead-end roads with the exception of private access drives. The preferred method of turnaround is to provide a cul-de-sac. Local streets may utilize alternate turnaround designs such as "T", "Y", or "Branch" turnarounds. Turnaround dimensions shall meet the dimensional requirements illustrated in Figure 3.5.10 and defined on Table 3.5.19 below.

1.

Rights-of-way: The right-of-way width at the turnarounds will be a minimum of the required for the street classification or a minimum of ten feet beyond the edge of turnaround pavement, whichever one is greater.

2.

Parking is not permitted within the area of the required turnaround. If parking is provided it must be outside the turnaround travel lanes.

FIGURE 3.5.10
CUL-DE-SAC AND TURNAROUND REQUIREMENTS

TABLE 3.5.10
CUL-DE-SAC AND TURNAROUND DIMENSIONAL REQUIREMENTS

Turnaround Type	'A' Paving Width	'B' Cul-De-Sac Radius Min.	'C' Offset Min.	'D' Edge Radius Min.	'E' Edge Radius Min.
Residential	Per Road Class	40'	30'	25'	35'
Commercial	Per Road Class	70'	60'	35'	45'

 

3.5.11

Private access drives. Private access drives shall be permitted to serve no more than three land-locked residential lots where, due to special circumstances created as a result of necessary unusual platting configuration, or as a result of special physical features, the property could not otherwise be developed. No more than one such drive shall be approved per subdivision development submission and must be approved as part of the original plat for the subdivision, section, or phase. These drives are exempt from paving requirements but shall be, as a minimum, surfaced with crusher run stone, six-inch depth and a minimum width of 16 feet. Private access drives shall have the same right-of-way as is required for local streets.

3.5.12

Subdivision entrance from an existing street. When a subdivision entrance ties into an existing public street or road this entrance shall meet all state and local requirements for intersection design. This shall include adding required turn lanes, acceleration and deceleration lanes, additional right-of-way and all necessary signs and signals that may be required for the existing public road as well as those required for the subdivision street.

3.5.13

Alleys. Alleys, 20 feet in width, may be required at the rear of all lots used for multifamily, commercial, or industrial development. Alleys in single-family residential subdivisions shall not be permitted, unless the developer provides evidence satisfactory to the Greene County Board of Commissioners of the need for such alleys Dead-end alleys without a turnaround are prohibited. Alleys shall conform to the design requirements for local streets except that the county may require that the base and paving structure be equal to that of a higher street classification if the anticipated loading of the pavement warrants.

3.5.14

Development along arterial street. Where a subdivision abuts an existing arterial street or railroad right-of-way, an access street approximately parallel to and on either or both sides of the existing right-of-way may be required by the Greene County Board of Commissioners. Direct access from a subdivision to the arterial street will not be permitted. A buffer zone restricting access to the arterial right-of-way may be used in conjunction with or in lieu of the access street.

3.5.15

Slope maintenance easements. Slope maintenance easements shall be required whenever, due to topography, additional width is necessary to provide finished slopes that conform to the requirements of Table 3.5.3.

3.5.16

Sidewalks. The inclusion of sidewalks within subdivisions is encouraged. When included, sidewalks shall be within a dedicated non-paved right-of-way of roads within the subdivision or other prescribed areas. The minimum paved width of sidewalks shall be five feet and a median strip of grassed or landscaped areas shall generally separate all residential sidewalks from adjacent streets except when contiguous to parking areas. Concrete sidewalks shall be constructed to the requirements of Georgia Department of Transportation Construction Standard 9031-W.

( Ord. of 8-8-2017 )