(A) General. In order to provide for streets of suitable location, width, and improvement to accommodate expected traffic and afford satisfactory access to police, firefighting, snow removal, sanitation, and road maintenance equipment, and to coordinate street development so as to compose a convenient system, avoid undue hardships to adjoining properties, and assure compatibility with long-range comprehensive plans, all streets shall be designed according to the geometric standards set forth in these regulations.
(B) Principles of design.
(1) Subdivision street design is the design of local and minor collector streets which are part of a functionally classified street and road system of an area (see App. §§ 4 and 5 for average dimensions by functional classifications). In designing and approving subdivision streets, the following factors shall receive consideration.
(a) Safety for both vehicular and pedestrian traffic.
(b) Efficiency of service for all users.
(c) Livability or amenities as affected by traffic elements in the circulation system.
(d) Economy of both construction and use of land.
(2) Design of major collector and arterial streets shall require special design and approval by the City Engineer. The following design guidelines are, therefore, specifically intended for streets within the subdivision, i.e., minor collectors and locals.
(C) Interpretation of design tables. The tables in App. §§ 4 and 5 represent average conditions and are included in these regulations to illustrate the hierarchy of functional classification. The figures in App. §§ 6 and 7 represent specific design standards for minor collectors and local streets, respectively. Design variation or control is based on terrain classification and development density as described below.
(1) Definitions of terrain classifications.
(a) Level. Cross slopes range of 0% to 8%.
(b) Rolling. Cross slopes range of 8.l% to 15%.
(c) Hilly. Cross slope of over 15%.
(2) Definitions of density classification in terms of gross land area.
(a) Low. 2 or less dwelling units per acre.
(b) Medium. 2.l to 6.0 dwelling units per acre.
(c) High. Over 6.0 dwelling units per acre.
(D) Design traffic volumes. The design hourly volume (DHV) or average daily traffic (ADT) is the accepted basis for design. In rural areas, the City Engineer may amend the design standards as determined by traffic demand analysis. However, the traffic volume does not always determine the type of curves to be used in designing low volume residential local and minor collector streets. Traffic volumes are a major factor to be considered for streets serving commercial and industrial areas, and the City Engineer is required to give special attention to these areas.
(E) Design speeds. Design speeds are not a major factor for urban residential local and minor collector design. As a general rule, the same rule can be applied to rural low volume roads in subdivision design. The sight distances and curve radii in App. §§ 6 and 7 are commensurate with average acceptable design speeds.
(F) Vertical grades. Drainage design may become critical where grades exceed 4%. For this reason, grades lower than the suggested tabular values are encouraged. Commercial and industrial streets shall be held to a maximum grade of 4%. Residential streets shall in no case exceed the tabular values. In order to provide for proper drainage, the minimum grade should be held to 0.5%. The maximum grade on the approach leg of any intersection shall not exceed 5% in hilly terrain and 2% in level terrain.
(G) Superelevation. Superelevation is usually not required in residential areas. It should be considered in commercial and industrial areas and for collector streets where operating speeds may exceed 30 to 35 miles per hour. Where superelevation is used, street curves should be designed for a maximum superelevation rate of 0.04 to 0.06 foot per foot (urban) and 0.08 to 0.12 foot per foot (rural).
(H) Horizontal alignment. Minimum centerline radii for horizontal curves shall be 225 feet. The minimum tangent distance between reverse curves shall be:
(1) Residential local, 100 feet.
(2) Residential minor collector, 150 feet.
(3) Commercial industrial collector, 200 feet.
(I) Intersections.
(1) Intersections, including median openings, should be designed with adequate corner sight distance. The recommended minimum corner sight distance is 200 feet for local streets and 300 feet for minor collectors. In order to maintain these distances, the City Engineer may recommend regulations to restrict the height of embankment, location of buildings and screening fences and landscaping, and other provisions necessary for intersection sight control.
(2) The minimum intersection angle shall be 75 degrees.
(3) Closely spaced offset intersections are undesirable. The minimum intersection centerline offset (jog) shall be 150 feet. To accommodate transitional tapers, turning lanes, and other potential roadway design requirements where needed, the City Engineer may recommend longer offsets.
(4) The minimum curb return radius at local streets shall be 15 feet and at residential collector streets 20 feet. The desirable radius is 25 and 30 feet, respectively. On commercial and industrial streets, the radius shall be 30 feet, except where traffic conditions may warrant a smaller radius. The use of three-centered curves may be required in commercial and industrial areas to accommodate the largest vehicles expected.
(J) Cul-de-sacs.
(1) The maximum length of a residential local street cul-de-sac shall be 600 feet. Wherever a minor collector street serves exclusively an industrial or commercial area, a cul-de-sac may be allowed and the length may be increased to 1,000 feet. This special provision shall be allowed only in areas which have a difficult access or are otherwise unsuitable for normal subdividing. However, a 48-foot pavement shall be required in all cases under this special provision.
(2) The minimum radii for cul-de-sacs shall be as follows.
(a) Local.
1. Right-of-way or outside, 55 feet.
2. Back-to-back of curb, 45 feet.
(b) Commercial/industrial.
1. Right-of-way or outside, 60 feet.
2. Back-to-back of curb, 50 feet.
(c) Chapter 152, Appendix § 7 represents specific design standards for residential (TYPE-1) and all other (TYPE-2) subdivisions.
(K) Auxiliary lanes. The City Engineer shall require construction of parking and turning lanes and transitional tapers where warranted.
(L) Sidewalks. Sidewalks shall be provided along both sides of streets used for pedestrian access, such as to schools, parks, or commercial areas. In all residential areas, the Commission may allow for a sidewalk on one side only. Minimum thickness shall be four inches Portland Cement Concrete. Minimum width shall be four feet.
(M) Subgrades and pavements.
(1) Minimum specifications. Minimum specifications for construction and materials shall be as set forth in the applicable sections of Standard Specifications of the State Highway Commission, except where the city has adopted a set of standards and specifications which are more stringent.
(2) Rigid pavements. Rigid pavements (air-entrained plain cement concrete) shall meet the following minimum requirements.
(a) Pavement thickness.
1. Eight inches on local streets.
2. Nine inches on residential collector streets.
3. Ten inches on commercial/industrial collector streets.
4. Special design on all other streets.
(b) Contraction joints.
1. Placed at a spacing of 20 feet or less.
2. Placed at every catch basin and manhole in line of pavement.
3. Extend throughout side strips and curbs to full width of pavement.
(c) Expansion joints.
1. With approved dowel bar assembly, shall be placed at street intersections.
2. Where shown on plans.
(3) Flexible pavements.
(a) Flexible pavements may be used and the construction of full depth asphalt pavements is encouraged. For full depth hot asphaltic concrete or hot asphalt emulsion, the minimum pavement thickness shall be the following.
1. Nine and one-half inches on local streets.
2. Eleven and one-half inches on residential collector streets.
3. Fourteen inches on commercial/industrial collector streets.
4. Special design on all other streets.
(b) In lieu of full depth asphalt construction, other flexible pavement types may be used as follows:
1. Nine inches crushed stone, three inches asphalt base mix, and one and one-half inches asphalt surface mix on local streets.
2. Nine inches crushed stone, four inches asphalt base mix, and one and one-half inches asphalt surface mix on residential collector streets.
3. Ten inches crushed stone, six inches asphalt base mix, three inches asphalt binder mix, and one and one-half inches asphalt surface mix on commercial/industrial collector streets.
(c) In no case shall the maximum lift exceed three and one-half inches.
(4) Remote local streets. Where, in the opinion of the Commission, a gravel street would be sufficient because of its remote location in the county, such gravel street construction standards must, at least, meet county gravel road specifications.
(Ord. 29-1984, passed 8-14-84; Am. Ord. 12-1993, passed 6-8-93; Am. Ord. 4-2019, passed 5-14-19; Am. Ord. 1-2023, passed 3-20-23) Penalty, see § 152.99