Municipal Design Standards Part 5 – Streets

5.01 APPROVALS, PERMITS, AS-BUILTS AND MAINTENANCE BONDS:

A. Plans and specifications for public street improvements must be certified by a professional engineer registered in the State of Iowa and utilize the NGVD of 1929.

B. Plans and specifications for public street improvements must be reviewed and approved by the City Engineer prior to construction.

C. Other local, state and federal permits may be required, depending on the circumstances. It shall be the responsibility of the Engineer of Record to acquire all applicable permits. A copy of all permits shall be provided to the City Engineer before construction.

D. The Engineer of Record is responsible to submit “Record of Construction” drawings to the Engineer on reproducible vellum or mylar.

E. A five-year maintenance bond covering defective materials and workmanship is required for all street improvements.

5.02 DESIGN RESOURCES:

A. Visit the American Association of State Highway and Transportation Officials, Web site

B. Iowa Department of Transportation Manuals Current editions with revisions:

• Standard Road Plans
• Road Design Details
• Road Design Manual
• Road Design Aids Manual

C. Iowa Department of Transportation “Urban Design Guides” and “Alternative Urban Design Guides,” current edition.

D. Iowa Department of Transportation “Standard Specifications for Highway and Bridge Construction”, current edition.

5.03 STREET CLASSIFICATION:

Streets will be classified according to their functional use as described below. Existing facilities may not fully comply.

Major Arterial Streets provide continuous routes for the movement of large volumes of all types of through traffic across the City and between the City and outlying areas. Geometric design and traffic control should emphasize the safe movement of through traffic and minimize property access. Access to major arterials shall be limited from local streets or individual driveways. Major arterials will typically be multi-lane streets and shall have separate turning lanes at intersections. Major arterials will connect to the Expressway system.

Minor Arterial Streets provide continuous routes for the movement of large volumes of all types of through traffic across the City and may also connect to outlying areas. Geometric design and traffic control should emphasize the safe movement of through traffic and minimize property access. Access to minor arterials shall be limited from local streets or individual driveways. Minor arterials will typically be two-lane streets with separate turning lanes at intersections, and may be multi-lane streets if warranted by traffic volumes.

Collector Streets provide for the movement of traffic between arterial routes and local streets as well as providing limited direct access to abutting property. Moderate amounts (2500 vehicles per day) of low speed (25 MPH) traffic, including bus traffic, may be carried on collector streets.

Local Streets serve as a means of access to abutting property. They are intended to be a low speed (25 MPH) and short trip routes, with usually less than 500 vehicles per day.

Industrial Streets are intended to carry commercial or industrial traffic.

5.04 RIGHT-OF-WAY WIDTH:

A. The minimum right-of-way width shall be provided as follows:

Major Arterial rights-of-way shall be no less than 100 feet in width,
Minor Arterial rights-of-way shall be no less than 85 feet in width,
Collector rights-of-way shall be 66 feet,
Local rights-of-way shall be 60 feet in width,
Cul-de-sac rights-of-way shall be 100 feet in diameter for local and 120 feet in diameter for industrial,
Industrial rights-of-way shall be 60 feet.
B. These widths do not provide for medians or boulevards if they are planned within the right-of-way.

5.05 TRAFFIC LANE WIDTHS AND LENGTH RESTRICTIONS:

A. All street widths shall be measured back-to-back of the curb.

B. The minimum traffic lane width will be 12 feet for arterials.

C. Local and industrial streets will have a minimum pavement width of 29 feet.

D. Arterial and collector streets shall have a minimum pavement width of 34 feet with provisions for bike lanes, except where turning lanes are present or 31 feet where bike lanes are not desired.

E. Cul-de-sacs shall be paved with a 29 foot wide paving. The outer edge of which shall be 10 feet inside the circumference of the right-of-way. The other radius from the stem of the cul-de-sac to the head shall be a minimum of 20 feet. Cul-de-sacs shall have a maximum length of 900 feet from the center of the bulb to the center line of the adjoining street.

5.06 SEPARATE TURNING LANES:

A. Separate turning lanes may be included on arterial streets but will generally not be included in other street design. Where separate turning lanes are required on the basis of a capacity analysis, use a 12-foot width for arterial streets and an 11-foot width for collector streets.

5.07 MEDIANS AND BOULEVARDS:

A. Medians or boulevards on arterial streets shall have a minimum width of 16 feet. At intersections, medians may be used to provide for a separate left turn storage lane.

B. Medians or boulevards which are included as a part of local or collector streets shall have a minimum width of 4 feet if paved or 9 feet if grassed. Paved medians on local and collector streets are discouraged.

5.08 DESIGN SPEED:

A. A design speed will be used to design the geometric features for arterial streets. The design speed will not be less than 35 miles per hour; however, posted speed limits may be less. The design speed will be used to establish geometric features including sight distance, intersections, etc. to current AASHTO standards.

5.09 CLEAR ZONES:

A. On streets with curbs, the clear zone shall be 3 feet for streets with a posted speed limit of 25 mph or less and 10 feet for streets with a posted speed limit greater than 25 mph. On streets without curbs, the clear zone shall be 10′ for two-lane and four-lane facilities.

B. Variances to clear zone requirements will be considered for overhead electrical facilities where compliance will significantly impact existing trees. In no case will a clear zone of less than 18 inches be allowed. A clear zone variance must be approved by the City Engineer.

5.10 STREET GRADES:

A. The maximum street grade for arterial, industrial and cul-de-sac streets shall be 8%, for collector streets 10% and for local streets 12%.

B. When two streets intersect, the grade of the lower classification street shall be minimized to allow safe stopping and starting in adverse weather.

C. The minimum grade for streets shall be 0.5%, except around the bulbs of cul-de-sacs where the minimum grade shall be 0.7%.

5.11 CURVE RADIUS:

A. The minimum center line radius for curves shall be as follows:

Arterial (major and minor) – 1,000′

Collector – 350′

Local – 150′

Cul-de-sacs – 150′

B. Under no circumstances will variances be granted for radii less than 75 feet.

5.12 PAVEMENT CROSS SECTION:

A. All pavements shall have a 2% parabolic crown cross-section as shown in Figure 5.1.

5.13 CURB AND GUTTER SECTION:

A. Curbs shall be 6″ as shown in Figure 5.1. Roll curbs are not allowed.

B. Curbs shall be integral cast Portland cement concrete. There shall be no separation between the curb and gutter section and the pavement.

5.14 INTERSECTION CORNER RADIUS:

A. The corner radius at intersections will depend on the functional classification of the intersecting streets. These are the minimum criteria:

arterial – arterial 50 feet

arterial – collector 30 feet

arterial – local 25 feet

collector – collector 25 feet

collector – local 25 feet

local – local 25 feet

industrial 50 feet

alley – all Maximum allowable that will remain in the street R.O.W. (not more than 20′)

Corner radiuses may be enlarged on routes that will have significant truck or bus traffic.

B. See Figure 5.2 for typical intersection joint detail.

5.15 PAVEMENT MATERIAL AND THICKNESS:

A. The pavement slab shall be constructed of non-reinforced Portland cement concrete conforming the IDOT specifications C-3 mix or M-3 mix.

B. The minimum required pavement thicknesses are as follows:

Pavement thickness requirements are intended as a guide. Arterial street projects shall be designed on the basis of soil conditions and projected traffic loadings.

5.16 SUBGRADE, BASE, AND FILL SECTION REQUIREMENTS:

A. The subgrade shall be scarified to a depth of 6 inches below the pavement and compacted to 90% of Modified Proctor Density.

B. All fill sections shall be compacted to IDOT Type A limits.

C. All pavement construction will require a minimum 6″ thick aggregate drainable base and tile system constructed to IDOT standards. Pavement tile systems may be used for sump pump discharge tiles required by Part 9, Storm Sewers and Stormwater Management Facilities. Tile shall be 6″ diameter when used in conjunction with sump pump discharges.

5.17 AREA BETWEEN THE SIDEWALK AND THE CURB (PARKWAY):

A. The parkway shall slope to the street at a rate of ½ of an inch vertical per horizontal foot.

B. In residential areas, the parkway shall be grassed except in such areas that the parkway is so narrow that grass does not grow well. In these narrow areas, the alternate materials described in paragraph C may be used upon approval of the Engineer.

C. In commercial areas, alternate materials may be used in the parkway upon approval of the City Engineer. These materials include exposed aggregate concrete, asphalt and bricks or concrete pavers on an asphalt or concrete base.

*With bike lanes. **See 5.15B.