§ 34-218. Roadway design.

(a)

Street grades and design speeds.

(1)

Minimum grade for all local and minor collector streets shall be 1.5 percent. Minimum grades for all major collector and arterial streets shall conform to state DOT practice.

(2)

Minimum grade of less than 1.5 percent on a local street may be approved by the department, based on adequate engineering designs, where at least 1.5 percent cannot reasonably be achieved due to topographical limitations imposed by the land. In such cases, a record drawing and such computations as necessary shall be provided after construction to establish that the street will drain in accordance with these regulations. Street sections where unacceptable pooling, excessive spread at catch basins, or other hazardous conditions occur shall be reconstructed or otherwise improved to eliminate such conditions.

(3)

Minimum vehicle design speeds and maximum grades allowable in the city by street classification shall be as shown in Table 9-A.

(4)

Maximum grade on any cul-de-sac turnaround shall be six percent.

Table 9-A
Minimum Design Speeds and Maximum Grades

Street Category	Maximum Grade	Design Speed
Principal arterial	6%	60 MPH
Major arterial	8%	50 MPH
Minor arterial	10%	40 MPH
Major collector	10%	40 MPH
Minor collector	10%	30 MPH
Local	15% *	20 MPH

 

^* Grades between 12 percent and 14 percent shall not exceed a length of 150 feet and shall require an "as-graded" survey prior to the installation of the curb or utilities. The distance shall be measured as the tangent length between points of curvature.

(b)

Vertical street alignment.

(1)

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).

(2)

Constant (K) values are shown in Table 9-B for both desirable and minimum acceptable ("hardship") conditions. In all cases, the "desirable" value shall be used, unless it cannot be achieved due to topographic conditions beyond the developer's control. In such hardship situations, the department may approve a lesser value to the extent required by the hardship situation, but in no event less than the value shown in the Table as "minimum."

Table 9-B
Constant (K) Values for Vertical Curves

	Crest Curves		Sag Curves
Street Category	Minimum	Desirable	Minimum	Desirable
Principal arterial	200	320	125	155
Major arterial	100	170	80	110
Minor arterial	55	80	55	70
Major collector	55	80	55	70
Minor collector	30	30	35	35
Local	10	10	20	20

 

(c)

Horizontal street alignment.

(1)

All new streets shall adhere to the following standards governing horizontal curvature and superelevation:

Table 9-C Horizontal Curves

Street Category	Minimum Radius (FT)	Maximum Superelevation
Principal arterial	1333	0.06
Major arterial	833	0.06
Minor arterial	560	0.04
Major collector	560	0.04
Minor collector	300	0.04 *
Local	120	0.00

 

^* No superelevation will be allowed on minor collectors internal to residential subdivisions.

(2)

Superelevation for horizontal curves shall be calculated utilizing the following formula:

R = minimum radius curve.

v = vehicle design speed (MPH).

e = rate of superelevation (decimal of a foot rise per foot roadway).

f = side friction factor.

R

=

v 15(e + f)

 

 

Vehicle Design Speed (v)	30	40	50	60
Side Friction Factor (f)	.16	.15	.14	.12

 

(3)

Widening section along existing streets shall be designed reflecting existing curvature and superelevation, if any, unless the existing street has been included in a specific design by the city or state DOT which calls for different standards, in which case the project will be coordinated with the overall design.

(4)

Superelevation runoff. Roadway edge curves shall be provided for tangent runout (bringing edge from a normal crown to centerline elevation) and superelevation runoff (from the end of tangent runout to the point of design superelevation) in accordance with design standards of the state department of transportation or other professional engineering standards.

(5)

Tangents and compound curves. Between reverse horizontal curves there shall be not less than the minimum centerline tangents shown in Table 9-D, unless otherwise specified by the state department of transportation. Compound radii curves are prohibited. At least the "desirable" length shall be provided, unless hardship conditions of topography or property configuration will not allow lengths greater than those shown as "minimum." For compound circular curves, the ratio of the flatter radius to the sharper radius shall not exceed 1.5 to 1.

Table 9-D Tangents

Street Category	Minimum Tangent Length	Desirable Tangent Length
Principal arterial	150 feet	180 feet
Major arterial	125 feet	150 feet
Minor arterial	100 feet	120 feet
Major collector	100 feet	120 feet
Minor collector	75 feet	90 feet
Local	50 feet	60 feet

 

Note: Minimum tangents are based on the distance traveled in 1.7 seconds at the design speed for each category of street. Desirable length is based on distance traveled in 2.0 seconds.

(d)

Horizontal and vertical clearances.

(1)

Horizontal clearances.

a.

A shoulder of no less than 11 feet from the back of curb or edge of pavement, appropriately graded and having gentle slopes of not more than 0.5 inch per foot and rounded cross-sectional design shall be maintained along all streets. Beyond the shoulder but within the right-of-way, slopes shall not exceed one foot of rise for each two feet of horizontal distance on a cut slope, and one foot of fall for each three feet of horizontal distance on a fill slope.

b.

Along all public streets, a clear zone shall be provided for a minimum distance of six feet from back of curb or edge of pavement wherein nothing may be located above ground level except traffic/street signs, public utility structures, and mailboxes.

c.

At selected locations, such as the outside of a sharp curve, a wider clear zone with greater horizontal clearances provided to any roadside obstruction may be required.

d.

The department of transportation, in accordance with O.C.G.A. § 32-6-51, is authorized to remove or direct the removal of any sign, signal, device, or other structure erected, placed, or maintained on the right-of-way of a public road which, because of its nature, construction, or operation, constitutes a danger to, or interferes with the vision of, drivers of motor vehicles.

(2)

Vertical clearances. Vertical clearance at underpasses shall be at least 14.5 feet over the entire roadway width.

(e)

Traffic calming for local residential streets.

(1)

Subdivision streets shall be designed in accordance with the city traffic calming guide so as to encourage and maintain maximum operating speeds in the 25 to 30 miles per hour range. The maximum length of roadway section between speed control points, as defined by the traffic calming guide, shall be 500 feet.

(2)

The traffic-calming plan is subject to review and approval by the department of transportation. The director of the department of transportation may grant modifications.

(Ord. No. 2013-01-02, art. 9, § 9.5, 1-29-2013)