All applications for development approved by the Board of Supervisors shall conform to all the following minimum standards and requirements, except those plats referred to in Chapter 87 as Auditor’s plats.
(Ord. 317 – Apr. 24 Supp.)
1. Large Lot Subdivisions. Whenever the area is divided into lots of such size that there are indication that the lot could eventually be re-subdivided into smaller building lots, consideration shall be given to the street and lot arrangement of the original subdivision so that additional minor streets can be opened which will permit a logical arrangement of small lots.
2. Street Design Standards. In new developments, road siting and street network are important considerations. To maximize storm water filtration and infiltration, natural drainage patterns shall be preserved whenever possible and, to the maximum extent feasible, streets (and other impervious surfaces) shall not be located in low areas or on highly permeable soils. The street design standards defined in Table 88-1 apply to the construction of new streets and roads.
A. Half Streets. The platting of half streets shall not be permitted.
B. Off-Set Streets. Off-set streets shall be avoided.
C. Private Streets. Private streets are permitted, provided they serve four (4) or fewer lots only in subdivisions of not more than four (4) lots. Private streets shall be designed in accordance with the requirements listed on Table 88-1; however, pavement requirements shall not apply to private streets.
Table 88-1 - Street Design Guidelines
Element | Required Size/Specifications |
Element | Required Size/Specifications |
Rights-of-Way* | Rural Cross-section: Minimum of fifty (50) feet. Circular portion of a cul-de-sac: Minimum radius of fifty-five (55) feet. Lot Corners at Intersecting Streets: Minimum twenty-five (25) feet radius Existing County Roads: Minimum of sixty (60) feet of right-of-way from centerline of existing roads shall be deeded to the County for potential future improvements. |
Paved portion of roadway† | 22 feet in width |
Paved portion of cul-de-sac | 45-foot radius with minimum 22 feet paved travel lanes (remainder may be placed in landscaped island) |
Shoulders | 4 feet in width |
Foreslopes | 3:1 slope |
Ditch | 2 feet deep; 6 feet wide |
Backslopes | 3:1 slope |
Pavement Crown | 1.5% to 2.5% |
Pavement Thickness | Portland Cement - 7 inches Asphalt Cement - 4 inches of base, 2 inches of wearing course, and 4 inches of sub-base |
Horizontal and Vertical Curvature | Shall meet standards outlined in Iowa's Statewide Urban Design and Specifications Program (SUDAS) Geometric Design Table. |
A. * Upon approval of the County Engineer, the right-of-way width for local residential streets may be reduced in cases where the topography or special conditions make a right-of-way of less width more suitable. B. † Reduction of Pavement Widths. Upon approval of the County Engineer, the pavement width for local residential streets may be reduced in cases where the topography or special conditions make less width more suitable. | |
D. Dead-End Streets. The terminus of dead-end streets shall be appropriately designed for the amount of traffic generated as based on the number of development lots taking access from the street in accordance with the requirements listed on Table 88-2. The length of a dead-end street is measured along the centerline from the center of the cul-de-sac or turning-T (hammerhead) to its point of intersection with the centerline of the nearest through street.
Table 88-2 - Dead-End Street Lengths
Terminus Type | Maximum Street Length | Maximum Number of Development Lots |
Cul-de-sac (with or without island) | 1,320 feet | 20 lots |
Turning-T (hammerhead) | 300 feet | 6 lots |
E. Street Names. Street names for streets which are extensions of existing streets or roads shall be the same. Street names shall be subject to Planning and Zoning Commission and Board of Supervisors approval and shall conform to the requirements of Chapter 32, Road Identification and Address Numbering System.
F. Relation to Adjoining Street System. The arrangement of streets in new subdivisions shall make provision for the continuation of the principal existing streets in adjoining subdivisions, or for a proper intersection where said streets in the new subdivision shall connect therewith, or their proper projection where adjoining property is not subdivided insofar as they may be necessary for public requirements. The width of such streets in new subdivisions shall not be less than the minimum street widths established herein unless a differed required width is established by the Story County Engineer in order to provide continuity and/or connectivity with the adjoining street system. The street arrangement shall also be such as to cause no hardship to owners of adjoining property when they plat their own land and seek to provide for convenient access to it.