A. Roadway System Design.
1. The road system shall be designed to permit safe and orderly movement of traffic, to meet but not exceed needs of the present and future served population; to be simple and logical; to respect natural features, topography, and landscape, and to present an attractive streetscape.
2. The system shall conform to the official City street planning map and the general principles of the City's Comprehensive Plan. For streets not shown on the Comprehensive Plan, the arrangement of streets shall provide for the logical extension of existing streets.
3. The street network of a subdivision should provide for logical, continuous extensions of streets to subsequent later developments. Such extensions shall make provision when necessary with a temporary turnaround with a radius of at least 50 feet.
4. The system shall provide adequate traffic flow through a subdivision and provide at least two routes from each lot within the subdivision to the rest of the City, except as explicitly permitted by the approving authorities.
5. The applicant shall demonstrate to the satisfaction of the approving agencies that the distribution of traffic created by the subdivision will not exceed the design capacity of the proposed street system and its individual segments.
6. The categories, functions, and projected traffic loads of the street hierarchy are set forth in Table 166-2.
B. Pedestrian and Bicycle Systems.
1. A continuous pedestrian system shall be provided within each subdivision, designed to conduct pedestrians between every point in the subdivision in a safe manner. Subdivisions designated for industrial uses are exempt from this requirement.
2. In conventional subdivisions, the pedestrian system will ordinarily be provided by sidewalks placed parallel to and on both sides of each street, with exceptions permitted to preserve natural features, create visual interest, or maintain greenways and pedestrian ways proposed in the Comprehensive Plan.
3. In creative subdivisions, the pedestrian system may be an independent network diverging from streets but providing continuous pedestrian access between all points.
4. All aspects of the pedestrian system, including sidewalks and intersection crossings, must be designed to comply with the Americans with Disabilities Act.
5. Bikeways or recreational trails when required by the Subdivision Agreement shall be credited toward the satisfaction of pedestrian system and open space standards set forth by this ordinance.
C. Pavement Width.
1. Pavement width for each street classification is determined by parking and curbing requirements based on form or intensity of adjacent development.
2. Streets shall have a width and cross section as recommended in the Comprehensive Plan or the street planning map for the type of street involved. Final street paving and right-of-way widths shall meet City Public Improvement Design Standards. To promote economical development of streets, minimum pavement width should generally be used.
3. Partial width streets will normally be discouraged, except where they may be required to complete the remaining portion of a street already dedicated or where the Comprehensive Plan or the street planning map indicates that the alignment of street will straddle the property line.
D. Curbs, Gutters, and Shoulders.
1. Curbing shall be required for the purposes of safety, drainage, and protection of the pavement edge, as set forth in Table 166-4.
2. Requirements for curbs vary according to street function and the nature of adjacent development. Adjacent development is defined as urban or rural as follows:
a. Rural: Residential or predominately agricultural land use where average lot frontage exceeds 150 feet.
b. Urban: Residential land use where average lot frontage is less than or equal to 150 feet; or adjacent land uses include commercial, office, industrial, or civic use types.
3. Where curbing is not required, edge definition and stabilization shall be provided.
4. Where curbing is required, shoulders and drainage swales may be used only if soils or topography make the provision of shoulders preferable to curbs; or where the character of an area is preserved by the use of shoulders and drainage swales.
5. Shoulders, when developed, shall be at least eight feet in width on each side for all streets; and located within right-of-way. Swale width is site-specific. Shoulders shall consist of stabilized turf or other acceptable material.
6. All curbs shall provide ramps for accessibility by handicapped people consistent with the requirements of the Americans with Disabilities Act.
7. Curb construction shall follow standards established by the City of Mount Vernon.
E. Sidewalks.
1. Sidewalk requirements are determined by road classification and intensity of development, as set forth in Table 166-4.
2. Where sidewalks are not otherwise required by Table 166-4, the City may require their installation if necessary to provide access to generators of pedestrian traffic or major community features; to continue a walk on an adjacent street; to link parts of the city; or to accommodate future development.
3. In conventional development, sidewalks shall be placed generally parallel to streets within right-of-way. Exceptions are possible to preserve important natural features or to accommodate topography or vegetation; when applicant shows an alternative for a safe and convenient pedestrian system; or in creative subdivisions.
4. In commercial areas, sidewalks may abut curb.
5. Pedestrian easements at least 12 feet in width may be required through the center of blocks over 600 feet in length if deemed necessary by the approving authorities to provide access to schools or community facilities; or to maintain a continuous pedestrian network within and between subdivisions and districts of the City of Mount Vernon and its jurisdiction.
6. Sidewalks shall provide a clear path of at least five feet in width, free of any obstructions.
7. All sidewalks shall be constructed according to current standards in use by the City of Mount Vernon. Sidewalks shall be of concrete construction four inches thick except at points of vehicular crossing where they shall be six inches thick.
8. All sidewalks, crossings, and other segments of a continuous pedestrian system must comply with standards of the Americans with Disabilities Act.
F. Bikeways and Recreational Trails.
1. All off-street recreational trails shall be a minimum of eight feet in width for two-way traffic and comply with the Americans with Disabilities Act. Surfacing of trails shall be concrete. Alternate surfacing may be considered in appropriate areas. Gradients for bikeways and recreational trails should not exceed five percent, except for short distances.
2. Recreational trails may satisfy part of the requirements of this ordinance for sidewalks or open space.
3. All residential streets shall utilize bicycle safe drainage grates at storm sewer inlets.
G. Right-of-Way.
1. Measurement: The right-of-way of a street shall be measured from lot line to lot line, and shall be wide enough to contain the roadway, curbs or shoulder, sidewalks and sidewalk setbacks, other necessary graded areas, and utilities.
2. Any right-of-way that continues an existing street shall be no less than that of existing street.
3. The requirements for right-of-ways for functional categories of roads is set forth in Table 166-4.
4. Dedications: Dedications of right-of-way for collector, subcollector, community, or arterial streets shall be made consistent with the Comprehensive Plan.
H. Alleys. Alleys may be required in business areas and industrial districts for adequate access to block interiors and for off-street loading and parking purposes. Alleys may be approved in residential districts. Dead-end alleys shall be provided with a means of turning around at their terminus.
I. Street System Design Standards.
1. Pavement. All streets shall be paved to comply with the Public Improvement Design Standards of the City of Mount Vernon.
2. Continuity of Arterial or Collector Streets. No subdivision shall prevent the extension of arterial or collector streets through and beyond the subdivision. The subdivider may plan and design collector streets not designated in the Comprehensive Plan or the street planning map, subject to the approval of the City Council.
3. Cul-de-sacs.
a. Cul-de-sac streets designed to have one end permanently closed shall not exceed 300 feet in length from the first through street to the turnaround and shall be designed so that vision from entrance to end is not restricted.
b. The closed end of a cul-de-sac within a conventional subdivision shall have a turnaround with a street property line diameter of at least 110 feet in residential subdivisions. This diameter may be increased by the Planning and Zoning Commission if deemed necessary in the case of a commercial or industrial subdivision.
c. Cu1-de-sacs should generally be avoided in subdivisions.
4. Street Grades. Streets and alleys shall be completed to grades having been officially determined or approved by the City Engineer. All streets shall be graded to the full width of the right-of-way and adjacent side slopes graded to blend with the natural ground level. The maximum grade shall not exceed those published in the City Public Improvement Design Standards.
5. Street Intersections.
a. Streets shall intersect as nearly at right angles as possible, unless limited by topography, existing street alignments, or other clearly defined constraints, as provided for in the City’s Public Improvement Design Standards.
b. In most cases, no more than two streets should intersect at a single intersection.
c. New intersections along one side of an existing or proposed street shall, if possible, align with intersections on the other side of the street. Offsets between adjacent intersections shall measure at least 150 feet between centerlines.
d. Intersection design standards are set forth in the Public Improvement Design Standards.
6. Block Size. The length, widths, and shapes of blocks shall be suited to the proposed land use and design of the proposed subdivision. Blocks within subdivisions in the TR Traditional Residential zoning district should not ordinarily exceed 300 feet in length. Blocks in other districts will be defined by the definitions contained within the Comprehensive Plan. Blocks within rural subdivisions shall not exceed 1,320 feet.
7. Access to Major Arterials. When a new subdivision, except where justified by limiting conditions, involves frontage on a heavy trafficway, the street layout shall provide motor access to such frontage by one of the following means:
a. A parallel street supplying frontage for lots backing onto the trafficway.
b. A series of cul-de-sacs or short loops entered from and planned at right angles to such a parallel street, with their terminal lots backing onto the highways.
c. A frontage road separated by a planting strip from the highway to which a motor access from the frontage road is provided at points suitably spaced.
d. A service drive or alley at the rear of the lots.
Where any one of the above mentioned arrangements is used, deed covenants or other means should prevent residential driveways from having direct access to the trafficway.
In general, streets shall be platted with appropriate regard for topography, creeks, wooded areas and other natural features lending themselves to attractive treatment.
8. Railroads. If a railroad is adjacent to or otherwise affects the design or street layout of the subdivision, the subdivision plat should:
a. Be so arranged as to permit, where necessary, future grade separations at highway crossings of the railroad.
b. Border the railroad with a parallel street at a sufficient distance from it to permit deep lots to back on to the railroad; or form a buffer strip for park, commercial, or industrial use.
c. Provide cul-de-sacs at right angles to the railroad so as to permit lots to back on the railroad.
9. Street Names. All newly platted streets shall be named and in a manner conforming to the prevailing street naming system. A proposed street that is obviously in alignment with other existing streets as indicated on the street planning map, or with a street that may logically be extended although the various portions be at a considerable distance from each other, shall bear the same name. Names of new streets shall be subject to the approval of the City Council in order to avoid duplication or close similarity of names, while at the same time providing for consistent and appropriate street names.
10. Street Tree Planting. Trees may be planted on the parking of all newly platted streets in conformance with the Code of Ordinances, City of Mt. Vernon, Iowa.
11. Other design standards shall be as set forth in the Public Improvement Design Standards.
J. Utility Locations in Public Right-Of-Ways.
1. See Exhibit A. The standard location drawing for public utilities constructed within the street right-of-way shall be in conformance with current City of Mt.Vernon building design standards. Utilities shall be constructed in those locations in so far as possible.
2. Sanitary sewers shall be constructed outside of the street pavement areas in the right-of-way or adjacent to the right-of-way in public sewer easements.
Residential Street
| Function Type
|
Lane, Court, or Cul-de-sac | Street providing private or controlled access to no more than twelve housing units. |
Local | Provides frontage to lots and carries traffic with origin or destination on the street itself. Carries least traffic at lowest speed. Local residential streets usually do not interconnect with adjoining neighborhoods or subdivisions. |
Collector | Conducts and distributes traffic between local streets and major streets in the community. Carries larger volume of traffic. Residential collectors interconnect and provide through access between residential neighborhoods. Collector streets should preserve one through traffic lane in each direction, without encroachment by parking. |
Minor Arterials | Provides community wide access between residential neighborhoods and to other activity centers in Mount Vernon, including uptown and major commercial facilities. Minor arterial streets should preserve one through traffic lane in each direction, without encroachment by parking. |
Major Arterials | Inter-regional road in the street hierarchy. Conveys traffic between activity centers, often at high speeds and with limited access. Should be excluded from residential areas. |
Residential Street Type | Maximum Grade | Pavement Width
|
Cul-de-sac | 12% (5%)* | 28 feet |
Urban Local | 12% (5%)* | 28 feet |
Rural Local | 12% | 28 feet |
Collector | 10% | 31 feet |
Arterials | 8% | 49 feet ** |
* Denotes maximum street grade within 50 feet of an intersection.
** A different pavement width section may be specified by the Comprehensive Plan, the City of Mount Vernon, or the requirements of the Iowa Department of Transportation.
Residential Street Type | Pavement Width | Curb/ Shoulder | Sidewalk | Minimum Sidewalk Setback (Note 1) | Total ROW |
Residential Street Type | Pavement Width | Curb/ Shoulder | Sidewalk | Minimum Sidewalk Setback (Note 1) | Total ROW |
Cul-de-sac | 28 feet | Required | Both sides | 6 feet | 60 feet at approach 110 feet diameter |
Local | |||||
Rural | 28 feet | Not Required | Not Required | NA | 66 feet * |
Urban | 28 feet | Curb | Both sides | 8 feet | 60 feet in other districts* |
Collector | |||||
Rural | 31 feet** | Not Required | Not Required | NA | 66 feet * |
Urban | 31 feet** | Curb | Both sides | 8 feet | 60 feet in TR District, 66 feet in other districts* |
Arterials | |||||
Arterial right-of-way design and width is determined by state standards and designation of individual street or roadway segment. | 49 feet** | Required in urban settings | Required in urban settings | 8 feet | 80 feet minimum** |
* Right-of-way widths for these classes of street may be modified within the Creative Subdivisions.
** A different pavement width section may be specified by the Comprehensive Plan, the City of Mount Vernon, or the requirements of the Iowa Department of Transportation.
Note 1: Sidewalks shall generally be set back one foot from the property line, as provided by the Public Improvement Design Standards. Minimum sidewalk setbacks from back of curb are established in this table.