§ 17.32.090. Street design standards.

A.

Guardrails. In areas of excessive fill or steep back slopes, roadside guardrail shall be installed consistent with the standards in the latest version of "Roadside Design Guide" as published by the American Association of State Highway and Transportation Officials (AASHTO).

B.

Pavement design. A pavement design report shall be prepared for all street projects by a registered professional engineer, or other qualified professional approved by the City Engineer, and submitted to the City Engineer for review and approval. The design shall be based on site characteristics (e.g., soils) and based on at least a twenty-year performance period traffic volume; however, the minimum design lane equivalent eighteen thousand (18,000) pound single axle load (ESAL) used in the pavement design must not be less than fifty thousand (50,000) ESAL. Pavement thickness shall be consistent with the standards contained in the current AASHTO "Guide for Design of Pavement Structures" or the current Asphalt Institute Manual Series No. 1 (MS-1).

C.

Cut and fill slopes. Cut and fill slopes shall meet the standards in Exhibit 32-1. When these standards can not be met because of steep terrain, limited right-of-way, or other site constraint, a geotechnical report shall be prepared by a professional engineer and submitted to the City Engineer for review and approval. The geotechnical report shall contain, at a minimum, the following:

1.

An explanation of why the standards can not be met.

2.

A description of the soil types encountered at the site and their properties.

3.

An assessment of soil slope stability.

4.

A copy of any boring logs, if any were taken.

5.

A description of the recommended design, supported by design calculations.

If other slope stabilization measures are necessary (e.g., soil pinning, retaining walls), the geotechnical report shall also include the following information:

1.

Settlement characteristics of the soil, including amount of settlement expected, time rate of settlement, surcharge or camber if required.

2.

Bearing capacity of the soil.

3.

Expected skin friction of the soil if piles or drilled shafts are proposed.

4.

Soil pressure, stability, and alternates (if a soil retaining wall is being considered).

D.

Culs-de-sac. Culs-de-sac must meet a forty-two and one-half (42½) foot radius from center of cul-de-sac to back of curb, a fifty-five (55) foot radius on the right-of-way, and cannot be longer than five hundred (500) feet.

Exhibit 32-1. Standards for back slope and fill slope under normal conditions

Cut Depth	Allowable Back Slope
0—5 feet	5:1
5—10 feet	4:1
10—15 feet	3:1
15—20 feet	2:1
>20 feet	1.5:1

 

 

Fill Height	Allowable Fill Slope
0—10 feet	6:1
10—20 feet	4:1
20—30 feet	3:1
>30 feet	2:1

 

E.

Temporary dead-end streets. When a street terminates in the first phase of a multi-phase project or where it is intended that the street will continue into an adjoining vacant parcel when it develops, a temporary cul-de-sac shall be provided. Upon completion of the connection, the temporary cul-de-sac shall be removed and the street cross-section completed.

F.

Street grades. Street grades shall conform to the standards of Exhibit 32-2.

Exhibit 32-2. Street and alley standards

	Principal Arterial	Minor Arterial	Collector	Local Street	Alley
Right-of-way width (feet)	110	100	80	60	20
Maximum grade (percent)	5	7	10	10	10
Minimum grade (percent)	0.5	0.5	0.5	0.5	0.5

 

G.

Curved Streets. Curved collector streets shall have a centerline radius of not less than two hundred fifty (250) feet. Curved local (minor) streets shall have a centerline radius of not less than one hundred (100) feet.

(Ord. 2950, 2007; Ord. No. 3056, 2010)