180.12  DESIGN STANDARDS AND REQUIRED IMPROVEMENTS.
   1.   General Requirements.
      A.   The design of any subdivision shall comply with the standards of this ordinance, provide for the orderly growth and development of the City, demonstrate consistency with the North Liberty Comprehensive Plan and any specific adopted district plans, and take into consideration the natural features of the site and patterns of adjacent development.
      B.   The subdivider of property shall be responsible for constructing all public improvements associated with the proposed subdivision according to design standards established by the City, except for special circumstances such as oversizing of facilities, as determined by the City.
   2.   Use Buffers - Yards and Screening.
      A.   Definition and Purpose.  "Use Buffer" means a yard or portion of a yard along with plantings, berming, landscaping, or fencing, which provides both a physical separation and screening between potentially incompatible land uses or between a land use and a public road. Buffer yards are required to separate different land uses from each other in order to eliminate or minimize potential nuisances such as dirt, odor, litter, noise, glare of lights, signs and unsightly buildings or parking areas.
      B.   Relationship to Zoning Required Yards.  Use buffers may be located partially or completely within front, side, or rear yards required to meet Zoning Ordinance setback requirements; however, use buffers must meet the requirements outlined in the following General Requirements section.
      C.   General Requirements.
         (1)   Use Restrictions.  Buffer yard areas shall contain mainly landscaping and turf. No principal buildings, outbuildings, parking lots or aisles, outside storage or display, or any other active use shall be located within the yard area, with the following exceptions:
            (a)   Drives accessing the site, but only if perpendicular to the buffer's length; and
            (b)   Pedestrian ways.
         (2)   Easement Required.  All buffer yard areas shall be established by easement recorded on the final plat, with clear delineation of maintenance responsibilities presented in the recorded final plat documents that will be recorded.
         (3)   Responsibility.  Establishment of the buffer yard easement and landscaping, and ongoing maintenance of the area, is the responsibility of the lot owner with the more intense land use, or in the case of arterial buffers, the single adjacent owner.
         (4)   Existing Incompatibilities.  This chapter is not applicable to lots established prior to the adoption date of this ordinance.
         (5)   Yards Required and Dimensions.  The type and width of buffer yard required between two adjacent parcels or between a parcel and a street is determined by the use or proposed use of all adjoining land, the zoning district or districts in which the property is located and the zoning districts adjoining the subject property, as specified in the following table.
 
TABLE 180.12-A - USE BUFFER TABLE - YARDS
Buffer Width
Buffer Location
Arterial street buffers, all residential districts
20'
On lot
Incompatible use buffers 1
All industrial districts abutting residential districts
50'
Industrial lot
All highway commercial districts abutting residential districts
20'
Highway Commercial lot
RM districts abutting RS districts
20'
RM lot
R-FB district abutting single-family residential districts
50'
R-FB lot
1  If uses are separated by a street right-of-way, or if a screen fence is constructed, the buffer yard width may be reduced by ½.
 
         (6)   Screening.  Adequate screening levels and type of screening shall take ground level and views from the adjacent property into consideration in observing the following requirements:
            (a)   In all cases when a use buffer is required, a green belt planting strip shall be established, consisting of evergreen trees and/or deciduous trees and plants of sufficient width and density to provide a visual screen. Earth mounding of berms may be used to achieve no more than four feet of the required screen;
            (b)   In cases where incompatible uses are directly adjacent, a screening fence constructed of masonry, brick, wood, vinyl, or similar material compatible with the less-intense zoning district shall be constructed in the buffer area in conjunction with the planting and berming plan. Such fence and plantings shall provide a solid screening effect six feet in height; and
            (c)   Buffer yard screening through the use of a fence only shall not be allowed.
         (7)   Buffer Plan Required. Prior to approval of a final plat, a buffer plan is required for all buffer areas. The buffer plan, illustrating plant type, size, quantity, location, planting specifications, and grading shall be prepared by a registered landscape architect.
         (8)   Plant Size.  All plants must at least equal the following minimum sizes. Larger plant materials may be required when necessary for immediate screening.
 
TABLE 180.12-B - BUFFER AREA PLANT SIZE - POTTED/BARE ROOT OR BALLED AND BURLAPPED
Shade trees
2 inch diameter
Half trees (Flowering Crab, Hawthorn, etc)
1-1/2 inch diameter
Evergreen trees
3 - 4 feet
Tall shrubs and hedge material (evergreen or deciduous)
3 - 4 feet
Low shrubs:
    Deciduous
24 - 30 inches
    Evergreen, upright
24 - 30 inches
    Evergreens, spreading
18 - 24 inches
 
         (9)   Plant Spacing.  Plant material centers shall not be located closer than three feet from the fence line or property line, and shall be planted to not conflict with public plantings. Where plant materials are planted in two or more rows, plantings shall be staggered in rows.
         (10)   Ground Cover.  All portions of the buffer yard not occupied by plantings or fencing shall be seeded or sodded with grass or ornamental groundcover.
         (11)   Existing Conditions. Any existing plant material or site topography which otherwise satisfies the landscaping standards may be used to satisfy the conditions of this chapter.
         (12)   Slopes. Turf slopes of all berms shall not exceed a 3:l ratio.
         (13)   Maintenance. Screening shall be maintained in perpetuity by the owner.
         (14)   Corner Visual Clearance.  On corner lots at street intersections in all districts, no structure, fence or planting material in excess of three feet in height above the street grade shall be permitted within a triangular area identified by connecting two points measured 25 feet from the intersection of the two lot lines forming the street intersection along each of those two lot lines.
   3.   Streets and Circulation.  The road system shall be designed to permit the safe, efficient, and orderly movement of vehicular and pedestrian traffic; to meet the needs of the present and future population served; to have a simple and logical pattern and allow that pattern to continue through adjacent properties; and to respect natural features and topography.
      A.   Streets and Driveways.  When a drive provides the frontage for one or more lots as required in the Zoning Ordinance, that drive shall be designated as a street and shall meet all design and construction regulations for streets contained in this ordinance and in the City's construction design standards.
      B.   Connectivity.  Subdivisions shall provide for continuation and extension of arterial, collector and local streets, sidewalks and trails in accordance with the following standards:
         (1)   Arterial streets shall be located and extended in general accordance with the Metropolitan Planning Organization of Johnson County (MPOJC) Arterial Street Plan and the North Liberty Comprehensive Plan.
         (2)   All streets, sidewalks, and trails shall connect to other streets, sidewalks, and trails within the development, and to the property lines to provide for their extension to adjacent properties. Each subdivision shall contribute to the larger interconnected street pattern of the City to provide for street connectivity between neighborhoods, multiple travel routes resulting in the diffusion and distribution of traffic, efficient routes for public and emergency services, and direct and continuous vehicular and pedestrian travel routes to neighborhood destinations.
      C.   Turning Lanes.  Separate turning lanes may be required on arterial streets and on streets connecting to arterial streets if existing or forecasted traffic warrants the lanes.
      D.   Cul-de-sacs.  Use of cul-de-sacs and other roadways with a single point of access should be avoided. Cul-de-sacs will be considered where it can be clearly demonstrated that environmental constraints, existing development, access limitations along arterial streets, or other unusual features prevent the extension of the street to the property line or to interconnect with other streets within or abutting the subdivision. In such cases, the maximum length of a cul-de-sac shall be no more than 900 feet measured from the centerline of the intersecting street to the center of the turn-around; the cul-de-sac turn-around shall be centered in the turn-around right-of-way; and the minimum outside radius of the pavement of cul-de-sac bulbs shall be 40 feet.  A center landscaped island may be installed if approved by the City as a part of the construction design plans. In such a case, the minimum radius shall be 11 feet, and the developer's agreement shall designate and set forth procedures for benefitted property owners or a homeowner's association to maintain the landscaped area. Said instrument shall provide that if said services are not provided as required therein, the City shall have the right to perform said services, and the cost thereof shall be a lien and charge against all of the subject lots.
      E.   Street Design Criteria Summary.  The following table provides a summary of requirements for various street types. If boulevards, bike lanes, or other non-standard street types are planned, additional right-of-way may be necessary.
 
TABLE 180.12-C - STREET DESIGN CRITERIA SUMMARY
 
Arterial
Collector
Local & Cul-de-sac
Cul-de-sac Turn-around s
Industrial
Minimum Right-of-way Width1
100' Major Arterial
85' Minor Arterial
66'
60'
110' diameter
120' in industrial areas
60'
Minimum Street Pavement Width
31'
31'
29'
80' diameter
29'
Maximum Grade2
8%
10%
12%
8%
8%
Minimum Grade
0.6%
Minimum Curve Radius3
1,000'
350'
150'
150'
150'
1Additional width may be required in some circumstances such as to maintain consistency within a corridor or where auxiliary lanes are required.
2When two streets intersect, the grade of the lower classification street shall be minimized to allow safe stopping and starting in adverse weather.
3Minimum curve radius may be shorter where designed for traffic calming, subject to approval of the City Council.
 
      F.   Curb and Gutter Sections.  Curbs shall be integral cast Portland cement concrete, with no separation between the curb and gutter sections of the pavement. The curbs shall be six inches in height and roll curbs are not allowed.
      G.   Intersection Corner Radius.  Corner radii at intersections shall be based on the following table:
 
TABLE 180.12-D - INTERSECTION CORNER RADII PAVING STANDARDS
Arterial street intersecting arterial street
50'
Arterial street intersecting collector street
30'
Arterial street intersection local street
25'
Collector street intersecting collector street
25'
Collector street intersecting local street
25'
Local street intersecting local street
25'
Streets in industrial area
50'
Alleys intersecting any street
Maximum possible in ROW but not more than 20'
 
      H.   Parkway.
         (1)   The parkway shall slope to the street at a rate of 0.5 inches vertical per horizontal foot.
         (2)   The parkway shall be landscaped with grass except in areas so narrow that grass will not grow well or in commercial areas where alternative materials are proposed to create a special environment aesthetically. In such areas, alternate materials may be used only upon approval of the City Engineer.
      I.   Dedication of Right-of-Way.  Land shall be dedicated to the City for all public street rights-of-way within the development and for any public street right-of-way that is needed for streets that abut or will abut the development.
   4.   Measurements and Construction Standards.
      A.   All right-of-way improvements shall be designed and constructed according to the design standards established by the City.
      B.   All street paving widths shall be measured and referred to from back-of-curb to back-of-curb.
      C.   The design speed will be used to design the geometric features, including but not limited to sight distance, intersections, and curve radii for arterial streets to current AASHTO standards; however, in no case shall said design speed be less than 35 miles per hour.
   5.   Street Intersections.
      A.   A maximum of four legs are allowed at any one intersection.
      B.   The distance between street intersections shall be at least 125 feet centerline to centerline.
      C.   Intersection angles of street center lines shall be between 80 and 100 degrees.
      D.   Dead end streets and alleys are not permitted except at subdivision boundaries abutting undeveloped areas. In such cases, a temporary turn-around for fire apparatus may be required to be constructed to City specifications.
   6.   Traffic Calming Features.  The street network, block length, and layout of lots should be designed in a manner that discourages speeding traffic and unsafe driving behavior. In order to minimize the potential for speeding traffic and create a safer environment for pedestrians and bicycles, the City may, in cases where it is warranted, require traffic calming features to be designed into the subdivision. These features may include but are not limited to discontinuous streets, curb extensions, raised crosswalks, medians, or traffic circles.
   7.   Street Names.
      A.   The City reserves the right to deny the use of street names that it determines are not in the public interest. Street names shall be consistent with the following standards:
         (1)   In order to ensure safe an efficient provision of public and emergency services, each proposed street name shall be distinct from other street names within the larger metropolitan area; and
         (2)   Street names that are overly lengthy, difficult to pronounce, or may be considered inappropriate or unappealing shall be avoided.
      B.   For new streets, the following rules apply:
         (1)   The term "street" should be used for a non-dead end roadway aligned in a north-south direction.
         (2)   The term "avenue" should be used for a non-dead end roadway aligned in an east-west direction;
         (3)   The term "boulevard," "road," or "drive" may be used for a roadway that is aligned neither in a north-south nor an east-west direction, but that changes direction or meanders; and
         (4)   The terms "lane," "court," "circle," or "place" should be used for cul-de-sacs or low volume loop streets.
      C.   Cul-de-sacs or low volume loop streets may use the same name as the roadway with which it intersects.  For example, a cul-de-sac that intersects with Rose Avenue may be named "Rose Court." However, if more than one cul-de-sac or loop street intersects with Rose Avenue, an additional "Rose" name may not be used.
      D.   Similar names may not be used for streets that are in different locations within the City. For example, the name, "Rose Drive," may not be used in one neighborhood, if there is already a "Rose Avenue" in a different neighborhood.
   8.   Private Streets.
      A.   Private streets in single family residential areas are not allowed.
      B.   Requests for private streets in multi-family, commercial, and industrial areas may be considered, provided that connectivity to adjacent properties is not needed. If private streets are approved, the subdivider must submit a legally binding instrument setting forth the procedures to be followed for maintaining private streets and providing garbage service, snow removal, street sweeping, and financing these services. Such costs shall be shared by all owners of property located within the subdivision, or designated portion thereof, through the use of an owners association or other entity satisfactory to the City. Said instrument shall provide that if said services are not performed as required therein, the City shall have the right to perform said services, and the cost thereof shall be a lien and charge against all of the owners of lots so designated in the subdivision.
      C.   Private streets shall be labeled as "Public Access Easement Street" on the plat.
      D.   Private streets shall be designed and constructed to the same standards as public streets.
   9.   Sidewalks, Trails, and Pedestrian Connections.  Public sidewalks, trails, and pedestrian connections shall be constructed in the public right-of-way according to the following standards:
      A.   The City's approved design standards and the approved North Liberty Trails Network Plan shall be observed for construction standards and location, respectively. The City will determine on which side of the street the wide sidewalk will be placed and the specific different width of the sidewalk.
      B.   Minimum five foot wide concrete sidewalks are required to be constructed along both sides of all local and collector streets.
(Ord. 14-01 – Feb. 14 Supp.)
      C.   All sidewalks and trails shall connect to other sidewalks and trails within the development and to the property line to provide for their extension to adjacent properties.
      D.   The subdivider is responsible for the construction of a public sidewalk along the frontage of private open space along any public open space dedicated to the City and along the frontage of other outlots as necessary for a continuous sidewalk system to be created.
      E.   In residential subdivisions, blocks longer than 600' must have mid-block pedestrian connections between adjacent streets, unless said connection is deemed to be unnecessary or infeasible and is waived by the City. At the time of subdivision, these connections must be platted as minimum 15 foot wide easements. If the connecting sidewalk is greater than five feet in width, the easement must be at least 20 feet wide. Within this easement, a sidewalk to City standards shall be constructed that is equal in width to the sidewalks to which it provides a connection. If the mid-block sidewalk connects to sidewalks of two different widths, the mid-block sidewalk must be equal in width to the wider sidewalk. The area and sidewalk within the pedestrian easement shall be maintained by adjacent property owners according to the developer's agreement in a manner similar to maintenance requirements for public sidewalks.
      F.   Where a trail extension, as identified in the Comprehensive Plan or an adopted trails plan, is located on the property being platted, the City may require installation of the trail, at the developer's expense, and any easement or dedication of land necessary for the trail.
   10.   Layout of Blocks and Lots.
      A.   Blocks.
         (1)   Blocks should be limited in size and be laid out in a pattern that ensures the connectivity of streets, provides for efficient provision of public and safety services, and establishes efficient and logical routes between residences and non-residential destinations and public gathering places.
         (2)   To provide multiple travel routes within and between neighborhoods, block faces along local and collector streets should range between 300 feet and 600 feet in length. For residential subdivisions, blocks should have a width sufficient to accommodate two tiers of lots. Longer block faces may be allowed in cases of large lot commercial, industrial, or rural residential development, or where topography, water features, or existing development prevents shorter block lengths, although mid-block pedestrian connections may be required. Block faces are measured from centerline to centerline of the intersecting streets.
         (3)   Block faces along arterial streets should be at least 600 feet in length. Intersecting collector streets should be spaced in a manner that provides adequate connectivity between neighborhoods but also maintains the capacity of the street for the safe and efficient movement of traffic. Longer block faces may be required along high capacity or higher speed arterial streets where the interests in moving traffic outweigh the connectivity between areas of development. The City may approve shorter block faces in high density commercial areas or other areas with high pedestrian counts.
      B.   Lots.
         (1)   Every lot shall be provided access and frontage as specified in the Zoning Ordinance on an approved public or private street.
         (2)   Lots shall be platted in a manner that will allow development to meet all Zoning Ordinance requirements. Lots must be of sufficient size to accommodate an adequate buildable area and area for required setbacks, off-street parking, and service facilities required by the type of use and development anticipated.
         (3)   Lots with multiple frontages must be platted large enough to accommodate front setback requirements along street-side lot lines.
         (4)   If a property with frontage only along an arterial street is proposed to be subdivided, a cross-access easement shall be provided by the property owner to all adjoining properties that front on the same arterial street.
         (5)   In residential areas, double and triple frontage lots should be avoided. Where the City determines such lots are necessary to overcome specific disadvantages of topography, land features, or access restrictions, the following standards apply:
            (a)   Multiple frontage and corner lots with only two frontages shall be platted with enough land area to accommodate the required front setback area along all frontages.
            (b)   Double and triple frontage lots where dwellings will have side or rear building facades oriented toward an arterial street shall provide a minimum 20 foot wide landscaped buffer area along the arterial street frontage. The buffer area shall be planted with a mixture of coniferous and deciduous vegetation approved by the City. The vegetation shall be required along with other public improvements for the property. Lots where dwellings will have front building facades oriented toward an arterial street are exempt from this requirement. If a buffer area was required during subdivision, no solid fences will be allowed within this buffer area. This restriction must be noted in the developer's agreement and on the plat. On corner lots, the landscaping within the buffer must be planted and maintained to comply with intersection visibility standards.
            (c)   Side lot lines shall approximate right angles to straight street lines or be approximately radial to curved street lines, except where a variation will provide a better street and lot layout.
            (d)   Residential lots shall not be designed with irregular shapes such as a flag or panhandle shape where the structure on the lot may be hidden from the street behind another structure.
   11.   Street Lights.  The subdivider shall submit the proposed street lighting placements for review by the City Engineer and City Council approval prior to placement. In all new subdivisions, decorative street lights shall be selected by the subdivider from an approved list provided by the City. All costs in connection with the furnishing of street lighting placements, decorative poles, light fixtures and related parts in new subdivisions shall be the responsibility of the subdivider.
   12.   Sanitary Sewers.  The subdivider shall provide a complete sanitary sewer system, including stubs, for each lot, which shall connect with a sanitary sewer outlet approved by the City Engineer. The sanitary sewer in each defined drainage area shall extend to the subdivision boundaries and beyond, as necessary to provide for the extension of the sanitary sewer to adjacent property, as determined by the City. In the event the City requires a sewer system greater than needed to service the subdivision under review, the City shall pay the developer for the difference in the costs of materials for the upsizing, and future subdivisions that connect with the subject system shall on a pro rata basis reimburse the City for the cost for the upsizing.
   13.   Storm Water Management.  The developer shall provide the subdivision with adequate drains, ditches, culverts, complete bridges, storm water quality features, storm water detention, storm sewers, intakes and manholes to provide for the collection, management, and removal of all surface waters as set forth in the City's Design Standards. These improvements shall extend to the boundaries of the subdivision and beyond, as necessary to provide for extension by adjoining properties and as determined by the City. The City will not pay for the excess cost when the subdivider is required under state law to manage the natural drainage including between adjoining lands.
   14.   Water Systems.  The developer shall provide the subdivision with a complete water main supply system, including hydrants, valves and all other appurtenances, which shall be extended into and through the subdivision to the boundary lines and beyond as may be necessary to provide for extension by adjoining properties, as determined by the City. The system shall provide for a water connection for lots and shall be connected to the City water system.
   15.   Private Utilities. The subdivider shall provide for installation or assurances acceptable to the City for installation of electric distribution lines, gas mains, telephone lines and other facilities in any new subdivision as are needed, as determined by the City, before final approval shall be given to the final plat. The subdivider shall be responsible for making the necessary monetary arrangements to provide for such utilities and, in addition, shall provide for underground facilities in residential subdivisions and commercial subdivisions with each utility company. In providing for said utility transmission lines, the subdivider shall make sure that adequate connections are provided to each lot.
   16.   Utilities in General.
      A.   All on-site utility lines, including but not limited to electric, communications, street lighting, and gas lines shall be installed underground except as hereinafter provided. For the purpose of this section, appurtenances and associated equipment such as, but not limited to, surface-mounted transformers, pedestal-mounted terminal boxes and meter cabinets may be placed above ground. Underground facilities need not be installed in the following instances:
         (1)   Any increase of service size including single phase to three-phase conversion; or
         (2)   Any new service when utility poles exist along abutting property lines that are not separated by any alley or public right-of-way and no additional utility poles are required.
      B.   The subdivider shall provide necessary easements in the subdivision for placement of all utilities including street lights and will submit to the City all proposed easements for use in the subdivision at the time the developer's agreement is presented.
      C.   The preliminary and final subdivision plat shall be presented to the designated representatives of the utility companies serving the subdivision area for the purpose of review and concurrence that sufficient easements have been obtained and shown on the final plat to accommodate placement of their particular utility service lines.
      D.   All proposed utility line locations in public rights-of-way or municipal easements shall be reviewed by the City for the purpose of avoiding locational, topographic, or other conflicts. In no case shall the permanent utility lines or appurtenances be constructed prior to authorization and approval of the final plat by the City.
   17.   Clustered Mailboxes.
      A.   All new residential or commercial developments that receive curbside delivery of mail shall have clustered mailboxes, unless an exception is approved by the United States Postal Service. The location of mailbox clusters shall be noted on the plat.
      B.   Mailbox clusters serving residential developments shall be conveniently located for residents, generally meeting the following criteria:
         (1)   Mailbox clusters should be located within approximately 600 feet walking distance from any residential property served by said mailbox cluster. Adjustments to this distance criterion may be approved when there are not enough lots within one block or 600 feet to form a cluster.
         (2)   Driveways shall be allowed no closer than 12 feet from the location of a clustered mailbox as measured along the curb line of the fronting street.
         (3)   Mailboxes must be located in a manner that will not violate the City's intersection visibility standards.
         (4)   Locations and design must be approved by the City and the United States Postal Service.
         (5)   Depending on the size and location of the clustered mailbox, the City may require a vehicular pull-over lane built to City specifications.
         (6)   Mailbox clusters shall be located on a concrete pad built to City specifications. To provide for pedestrian access, a five foot wide concrete sidewalk shall be provided from the mailbox cluster to the adjacent public street and sidewalk.
         (7)   The cost of installation, including but not limited to box units,  concrete pad, and sidewalk access, shall be borne by the developer, and subsequent maintenance shall be carried out by the property owners within the subdivision.
   18.   Specifications.
      A.   The type of construction, the materials, the methods and standards of subdivision improvements shall be according to City standards and all acquired permits.
      B.   Construction plans and specifications, including plans for subdivision erosion control measures, shall be submitted to the City Engineer for approval prior to construction. Construction shall not commence until the City Engineer approves the plans and specifications.
      C.   If the infrastructure and/or grading cannot be designed to comply with City standards, a new preliminary plat may be required at the discretion of the City.
   19.   Record of Construction Drawings.  The record drawing shall depict "as constructed" improvements, including deviations or revisions from the approved construction plans. All rim and invert elevations shall be surveyed and included on the record drawings. Stormwater management ponds, drainageways, and structures shall be surveyed and included in the plans, which shall be submitted by the developer's engineer with record drawing certification clearly stated on the drawings.
   20.   Inspections.
      A.   The City Engineer or designee shall inspect the installation of all public improvements in new subdivisions to insure compliance with the requirements.
      B.   The subdivider shall bear the cost of such inspection, which shall be the actual cost of the inspection by the City.
      C.   The subdivider shall provide qualified and appropriate inspection and construction management to ensure compliance with approved plans and specifications.
   21.   Off-Site Improvements.  When off-site improvements are necessary for the subdivision and development of a property, the subdivider shall be responsible for the extension of said improvements. Off-site improvements shall be designed and constructed according to plans and specifications approved by the City Engineer and shall be of sufficient size and capacity to serve the full area capable of being served by the type of improvement so that the City will not be required to construct parallel or duplicate facilities. If said infrastructure is greater in size than that needed to service the subdivision itself, the City, at its discretion, may share in the expense thereof. Such cost sharing shall be according to the procedure set forth in the developer's agreement. Any payment of excess costs by the City shall be pursuant to state law.
(Ch. 180 - Ord. 13-06 - July 13 Supp.)