City of Seward, NE Circulation System Design

Circulation system design is based upon the adjacent development, defined as either "urban" or "rural" as follows:

Rural: residential or predominately agricultural land use where average lot frontage exceeds 150 feet and subdivisions are not provided with urban services, including municipal water and/or sanitary sewer. Rural subdivisions are typically located within Rural Residential (RR) or Agricultural (AG) Districts outside of the City corporate limits, but within the City's extraterritorial jurisdiction (ETJ).

Urban: residential land use where average lot frontage is less than or equal to 150 feet and subdivisions are provided with municipal water or sanitary sewer service; or adjacent land uses include commercial, office, industrial, or civic use types.

At the discretion of the City, some sections of the circulation system within City corporate limits may be designed in accordance with a rural classification, limited to sections that have no current or future residential, commercial or industrial development. The limited sections are typically located within a designated floodplain, where development is prohibited.

Classification changes from "rural" to "urban" at the time of annexation.

At the time of annexation, the circulation system, including cartway, sidewalks, storm drainage, and all other aspects of the circulation system, shall be upgraded to urban classification standards.

The intent of the rural classification and requisite design requirements is to enable upgrade to urban design standards without complete reconstruction of the circulation system.

Reviewing agencies.

The reviewing agencies consist of the Street Superintendent, the City Engineer, and the Building/Zoning and Code Enforcement Director.

All plans including circulation system design and drainage facilities shall be reviewed and approved by the Street Superintendent, the City Engineer, and the Building/Zoning and Code Enforcement Director to ensure compliance with the requirements herein.

All plans reviewed and approved by the reviewing agencies are subject to subsequent review and approval by the City of Seward Planning Commission and the Seward City Council.

All exceptions, special circumstances, and other items approved by the reviewing agencies as provided for herein are subject to subsequent review and approval by the City of Seward Planning Commission and the Seward City Council.

Cartway system design.

The cartway system shall be designed: to permit safe and orderly movement of vehicular traffic; to facilitate pedestrian and bicycle traffic and minimize conflict between the various forms of circulation; 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.

The system shall conform with the Seward Comprehensive Plan. For streets not shown on the Seward Comprehensive Plan, the arrangement of streets shall provide for the logical extension of existing streets.

The street network of a subdivision shall provide for logical, continuous extensions of streets to subsequent future developments.

A temporary turnaround shall be located at the end of streets that will logically be extended. Construction of temporary turnarounds shall follow standards established by the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans.

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 reviewing agencies. Additionally, the system should be designed to discourage through traffic from using local streets.

Continuity of arterial or collector streets. No subdivision shall prevent the extension of Arterial or Collector streets through and beyond the subdivision. The subdivision developer may plan and design collector streets not designated in the Seward Comprehensive Plan, subject to the unanimous consent of the reviewing agencies.

Internal Connectivity Index.

The system should provide good internal street network connectivity. Internal connectivity shall be measured by a Connectivity Index, calculated as:

CI = N x L

Where:
CI	=	The Connectivity Index.
N	=	The number of nodes (including intersections and cul-de-sac heads) in a subdivision.
L	=	The number of street links defined by those nodes.

A desirable target for street connectivity is an index of 1.20 or greater.

Pedestrian systems, bikeways and shared-use paths.

A continuous and unobstructed pedestrian system consisting of a hard-surface paved sidewalk shall be provided within each nonindustrial subdivision, designed to conduct pedestrians between every point in the subdivision in a safe manner. Sidewalk design standards are located in § 410-40.3D.

In conventional subdivisions, the pedestrian system shall be provided by sidewalks placed parallel to and located on both sides of each street, with exceptions permitted to preserve natural features, create visual interest, or maintain greenways and pedestrianways proposed in the Seward Comprehensive Plan.

In innovative developments, the pedestrian system may be an independent network diverging from streets but providing continuous pedestrian access between all points. The pedestrian system for all innovative developments shall be approved by unanimous consent of the reviewing agencies.

All aspects of the pedestrian system, including sidewalks and intersection crossings, shall comply with the Americans with Disabilities Act (ADA) and the Public Right-of-Way Accessibility Guidelines (PROWAG).

Bikeways or shared-use paths shall be required if specifically indicated by the Seward Comprehensive Plan or in conjunction with any bikeways or shared-use paths in any phase of planning, development or design or if required by the City. Any land dedicated for shared-use paths development shall be credited toward the satisfaction of pedestrian system and open space standards set forth by this chapter.

Drainage.

All circulation systems shall be provided with a drainage system to remove excess stormwater. Design and construction of drainage facilities shall follow standards established by the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans.

Culvert size.

Where allowed, driveway culverts shall be a minimum size of 18 inches diameter.

Culvert sizing calculations shall be submitted to and verified by the City Engineer.

§ 410-40.3 Street hierarchy and design.

Characteristics of the hierarchy.

Streets shall be classified according to a street hierarchy, with design tailored to function.

The street hierarchy shall be defined by road function and projected average daily traffic (ADT), as calculated by trip generation rates calculated in accordance with the Institute of Transportation Engineers or other generally accepted standards.

Each residential street shall be classified and designed to meet appropriate standards for its entire length.

The applicant shall demonstrate to the satisfaction of the reviewing 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.

The street type, functions, minimum design speed and projected traffic loads of the street hierarchy are set forth in Table 40A.

Courts and Lanes may be designed and constructed to the minimal requirements provided herein on the condition that Courts and Lanes remain private or in private cooperative ownership. The subdivision agreement and plat shall clearly indicate that such streets are private and are not subject to City maintenance or acquisition. Courts or lanes shall be upgraded to the requirements of local street prior to a change from private to public ownership.

Cartway width.

Cartway width for each street classification is determined by parking and curbing requirements based on form or intensity of adjacent development.

To promote economic development of streets, minimum cartway width should generally be used. Minimum cartway widths are set forth in Table 40B.

In locations where the cartway width changes, those changes shall be accomplished using a tapered section. The minimum length of taper in feet shall be calculated by multiplying the offset of the cartway edge in feet by the design speed in miles per hour. Tapers shall not extend through intersections.

Curbs, gutters, and shoulders.

Curbing shall be required for the purposes of safety, drainage, and protection of the pavement edge, as set forth in Table 40B. Requirements for curbs vary according to street function and the nature of adjacent development.

Curbs, where required, shall be placed on both sides of all cartways. For cartways that are part of phased construction, the reviewing agencies may allow sections of curb to be omitted if the section of curb obstructs travel lanes in the next phase, provided that the subsequent phase is at least in the design process and construction of the subsequent phase is scheduled for construction to commence within 24 months of the placement of pavement in the current phase.

Requirements for curbs and minimum curb radii are set forth in Table 40B.

Where curbing is not required, edge definition and stabilization shall be provided to reduce edge degradation over time.

Where curbing is required, an exception may be granted by the unanimous consent of the reviewing agencies where the character of an area is preserved by the use of shoulders and drainage swales.

Shoulders, when developed, shall be at least eight feet in width on each side for all streets, shall begin at the same elevation as the roadway, and shall be located within the right-of-way. Swale width is site-specific. Shoulders shall consist of stabilized turf or other acceptable material.

All curbs shall be interrupted to provide a smooth transition between sidewalk ramps and road surface for accessibility by handicapped people consistent with the requirements of the Americans with Disabilities Act. The curb cut shall have a tapered section at each side of the sidewalk ramp.

(8)

Curb construction shall follow standards established by the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans. Curbs may be either combined curb and gutter constructed to a standard two-foot width or an integral curb.

Sidewalks.

Sidewalk requirements are determined by road classification and intensity of development, as set forth in Table 40B.

Where sidewalks are not otherwise required by Table 40B, the reviewing agencies may require their installation if necessary to provide access to generators of pedestrian traffic or major community features, or to continue a walk on an adjacent street, or to link parts of the City, or to accommodate future development.

In conventional development, sidewalks shall be placed parallel to streets within the right-of-way, with the outer edge of the sidewalk 18 inches inside the right-of-way. Exceptions are possible to preserve important natural features or to accommodate topography or vegetation; when an applicant shows an alternative for a safe and convenient pedestrian system; or in conservation of traditional neighborhood development (TND) subdivisions.

Pedestrian rights-of-way at least 15 feet in width may be required through the center of blocks over 600 feet in length if deemed necessary by the reviewing agencies 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 Seward and its jurisdiction. Such rights-of-way shall be dedicated to the public in the same manner as streets.

Sidewalks within pedestrian rights-of-way shall be centered within the right-of-way.

All sidewalks shall be constructed according to the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans.

Sidewalks shall be constructed of Portland cement concrete (PCC) utilizing an NDOT 47B mix design with Type 1PF cement with no less than a minimum compressive strength of 3,500 pounds per square inch (psi) at 28 days with a minimum thickness of four inches except at points of vehicular crossing (e.g., driveways), where sidewalks shall be a minimum six inches thick. The thickness standard is minimum actual thickness and not nominal.

All sidewalks shall have an adequately prepared sub-base of suitable soils with adequate preparation to prevent premature failure. Excavate and remove all topsoil prior to sub-base preparation. Sidewalk shall not be placed over topsoil. Poor soils shall be removed and replaced with a suitable aggregate material. The sub-base shall be scarified to a depth of at least six inches and uniformly compacted to within 95% prior to placement of concrete.

Sidewalks shall have a light broomed finish perpendicular to the direction of through pedestrian traffic.

Sidewalks shall provide a clear path of at least four feet in width, free of any obstructions.

In residential districts, sidewalks shall have a landscaped buffer zone of seven feet to 12 feet as measured from the back of the curb to the front edge of the sidewalk. Reductions to the size of the buffer zone may be granted in exceptional circumstances with the unanimous consent of the reviewing agencies.

To maintain adequate sight distances with unobstructed views of any conflicting vehicles or pedestrians, the buffer zone shall be landscaped predominantly with low-growing, mowable turf grass. Street trees are permitted within the buffer zone pursuant to the requirements of § 410-40.5 of this chapter.

Where approved by the reviewing agencies, in lieu of mowable turf grass, buffers zones of two feet or less may be paved with 3,500 psi PCC, minimum four inches thick, with a stamped surface pattern to delineate the buffer zone from the sidewalk. The stamped integral surface pattern shall provide both a visual and a tactile delineation between the sidewalk and the buffer zone.

(8)

In commercial districts, sidewalks may abut curbs, provided they are a minimum of six feet wide.

(9)

In industrial districts, sidewalks are not mandatory but may be required by the reviewing agencies to maintain a complete pedestrian circulation system.

(10)

Longitudinal grade.

The longitudinal grade of the sidewalk shall generally match the grade of the top of the curb. Sidewalks shall be smooth with horizontal and vertical alignments that are free of abrupt changes and which generally blend with the finish grading contours of the surrounding area.

Sidewalks not parallel to curb shall have longitudinal grades that do not exceed 5% except for short distances to overcome elevation differentials in the surrounding grade. Sidewalk longitudinal grades shall not exceed 8% under any circumstances.

(11)

The sidewalk shall have a transverse slope of 2% (one inch in four feet) in the direction of the curb. Exceptions may be granted in extraordinary circumstances where drainage must be directed away from the curb by unanimous consent of the reviewing agencies.

(12)

All sidewalks, crossings, and other segments of a continuous pedestrian system must comply with standards of the Americans with Disabilities Act (ADA).

Sidewalk grades shall exceed ADA requirements wherever possible. Grades shall be minimized and longitudinal grade changes shall be minimized.

Where sidewalks meet a street for access, a curb ramp shall be installed. Curb ramps shall conform to the Nebraska Department of Transportation Standard Plan No. 303-R3 Curb Ramps.

Bikeways and shared-use paths.

Bikeways and shared-use paths shall be required in subdivisions when specified as part of the Seward Comprehensive Plan, or in conjunction with any bikeways or shared-use path in any phase of planning, development or design, or if required by the City.

Construction standards.

All off-street shared-use paths shall be a minimum of 10 feet in width for two-way traffic and shall comply with the Americans with Disabilities Act. Shared-use paths shall be constructed according to the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans. Gradients for bikeways and shared-use paths should not exceed 5% except for short distances, and shall not exceed 8% without exception. Minimum dedicated bikeway and shared-use path right-of-way shall be 20 feet.

Shared-use paths shall be constructed of Portland cement concrete (PCC) utilizing an NDOT 47B mix design with Type 1PF cement with no less than a minimum compressive strength of 3,500 pounds per square inch (psi) at 28 days with a minimum thickness of six inches to support vehicles used for snow removal.

Shared-use paths may satisfy part of the requirements of this chapter for sidewalks or open space.

All residential streets shall utilize bicycle-safe drainage grates at storm sewer inlets.

Driveways.

Residential driveways shall be a maximum of 32 feet in width measured at the outer limit of the right-of-way. Residential driveways shall have a flare on both sides of the driveway, beginning at the front of the sidewalk and extending to the back of the curb or edge of cartway pavement when no curbs are constructed. Each flare shall have a width of four feet as measured at the back of the curb or edge of cartway pavement.

The maximum curb cut for a residential driveway shall be 40 feet in length.

There shall be a minimum 15 feet of separation from the edge of a driveway throat to edge of the adjacent driveway throat.

Exceptions to the maximum width and associated curb cut may be granted with the unanimous consent of the reviewing agencies.

Curb cuts shall be approved by the Street Superintendent and require a permit in accordance with § 340-4.1 of the City of Seward Municipal Code.

Driveways shall be paved from the outer limit of the right-of-way to the back of the curb or edge of cartway pavement with Portland cement concrete (PCC) utilizing an NDOT 47B mix design with Type 1PF cement with no less than a minimum compressive strength of 3,500 pounds per square inch (psi) at 28 days with a minimum thickness of six inches. The thickness standard is minimum actual thickness and not nominal.

Driveways shall slope toward the adjacent cartway and shall achieve a rise in grade of no less than six inches from the flow line of the gutter.

Alleys.

Alleys are prohibited outside of planned unit development (PUD) or traditional neighborhood development (TND) subdivisions. Alleys for PUD and TND developments may be approved with the unanimous consent of the reviewing agencies.

Where approved, alleys shall be paved with Portland cement concrete (PCC) utilizing an NDOT 47B mix design with Type 1PF cement with no less than a minimum compressive strength of 3,500 pounds per square inch (psi) at 28 days with a minimum thickness of six inches and shall have a minimum width of 14 feet. The thickness standard is minimum actual thickness and not nominal.

Parking is prohibited in alleys per § 382-4.8 of the City of Seward Municipal Code.

Right-of-way.

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 cartway, curbs or shoulder, sidewalks and sidewalk setbacks, other necessary graded areas, and utilities.

Any right-of-way that continues an existing street shall be no less than that of the existing street.

The requirements for rights-of-way for functional categories of roads is set forth in Table 40B.

Dedications. Dedications of rights-of-way for collector, community, or arterial streets shall be made consistent with the Seward Comprehensive Plan.

Street design standards.

Pavement.

All streets shall be paved in accordance with the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans. All streets shall be paved with either Portland cement concrete (PCC) or a 2-1/2-inch-think asphaltic concrete (AC) surface layer over a PCC base. Exceptions to hard surface pavement requirements are limited to the following:

[1]

Local and collector streets in rural subdivisions may utilize a gravel or crushed rock surface subject to submission of a petition by the platting owners binding themselves and all succeeding property owners to agree that all urban circulation system design requirements would be completed and paid for by a special assessment project if the subdivision were annexed by the City. Such petition shall waive any required resolution of necessity, any applicable limitations of the amount that could be assessed against subdivision property owners, including intersection costs, and other costs normally paid by the City in special assessment projects. Gravel roads shall be constructed with a surface course and a base foundation course graded to a 4% crown (1/2 inch for every foot of width) for proper drainage. Gravel used in paving rural roads shall meet the gradation requirements listed in the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans. The width of gravel from shoulder point to shoulder point shall equal the urban cartway width with curbs to enable future hard pavement without widening the sub-base. If hardsurfaced at the time of development, streets in rural subdivisions shall follow the requirements provided herein to enable upgrade to urban design standards without complete reconstruction of the circulation system.

Street pavement thickness shall relate to the role of the street in the hierarchy, subgrade conditions, and pavement type. Pavement thickness requirements are set forth in Table 40C. The thickness standard is minimum actual thickness and not nominal.

Cartways shall be paved with Portland cement concrete (PCC) utilizing a NDOT 47B mix design with Type 1PF cement with no less than a minimum compressive strength of 3,500 pounds per square inch (psi) at 28 days.

Pavements shall be allowed to cure for a minimum of seven days and meet a compressive strength of 3,500 psi prior to any vehicular loading, including construction vehicles and equipment.

Cartway cross-section.

Except at intersections, cartway paving shall be designed with the top of curbs level from one side to the other.

All paved cartway surfaces shall have a transverse slope (i.e., crown) of 2% from the center line to each gutter line. Where medians are present, the transverse slope shall be 2% from the face of the median curb to the gutter line. Where allowed, all unpaved cartway surfaces shall have a transverse slope of 4%.

On urban streets, the transverse slope from the top of the sidewalk to the top of the curb shall be a minimum of 2% (one inch in four feet) in the direction of the curb. Exceptions may be granted where drainage must be directed away from the curb by unanimous consent of the reviewing agencies. In such areas, the transverse slope away from the top of the curb shall not exceed 2%.

Minimum travel lane widths are set forth in Table 40D.

(e)

Cartways shall conform to the typical urban and rural cross sections provided in the Seward Standard Plans.

Horizontal alignment.

All changes in horizontal alignment shall be connected by circular curves. Minimum center-line radii are set forth in Table 40D.

A straight-line tangent having a minimum length of 100 feet shall be provided between adjacent noncompound horizontal curves where the sum of the curve radii is less than 600 feet.

Street grades and vertical alignment.

Maximum permitted longitudinal grades are set forth in Table 40E. In typical circumstances, the minimum permitted longitudinal gradient shall be 1.0%. In exceptional circumstances, the City Engineer may permit gradients of less than 1.0%; however, under no circumstances shall the gradient be less than 0.4%.

Approach grades at intersections shall not exceed 3.0%. Longitudinal grades at intersections shall be as close to 1.0% as possible, but under no circumstances shall the gradient be less than 0.4%.

Changes in longitudinal grades shall be designed using parabolic vertical curves. Where the algebraic difference between two grades expressed as a percent is less than 1.0%, no curve is required. The minimum length of vertical curves necessary to provide adequate safe stopping sight distance shall be determined using the following formula:

L = K x A

Where:
L	=	Minimum length of curve as measured in a horizontal plane.
K	=	A measure of curvature, values of which are set forth in Table 40D.
A	=	The algebraic difference between the grades of tangents to the curve, expressed as a percent.

In subdivisions that abut minor and major arterials which have not yet been improved to arterial standards, grades at intersections and abutting property grading shall be designed to accommodate the future grades of the arterial street.

Street intersections.

Unobstructed sight distances shall be provided at all street intersections and alley intersections for vehicular and pedestrian safety. Fences, walls, plantings or other obstructions greater than 24 inches in height above grade shall not be placed in the sight triangle established in Figures 40.1 through 40.5, with the exception of traffic control devices, light poles, railroad signals, parking meters, mailboxes mounted on posts no greater than four inches by four inches, and chain-link fences free of shrubbery, vines, or other visual obstructions.

Streets shall intersect at right angles (90°), unless limited by topography, existing street alignments, or other clearly defined constraints. In exceptional circumstances, the City Engineer may permit angles of intersecting streets different than 90°, but in such circumstances shall intersect as nearly as possible to right angles. Under no circumstances shall the angle of intersection deviate from right angles by more than 10° (i.e., 80° to 100°).

Only two streets shall intersect at a single intersection. Exceptions may be granted within traditional neighborhood development (TND) or planned unit development (PUD) subdivisions by unanimous consent of the reviewing agencies.

Local streets shall minimize intersections with major arterials. Intersections of all street types with major arterial streets shall not occur at intervals of less than 1,100 feet.

(e)

New intersections along one side of an existing or proposed street shall align with intersections on the other side of the street.

(f)

Offsets between adjacent intersections shall measure a minimum of 150 feet between center lines. The use of T-intersections is encouraged on local streets within the interior of a subdivision.

(g)

Minimum curb radii at intersections are set forth in Table 40B.

(h)

Where a curvilinear street intersects another street, a straight tangent section shall be required at the approach to the intersection. The length of this straight tangent section is dependent upon the radius of curvature. The minimum straight tangent lengths are set forth in Table 40F.

Roundabouts.

Roundabout intersections are generally used in residential districts as traffic calming devices, to improve safety by reducing conflict points, to reduce delay and accommodate capacity while avoiding signal or stop sign control, and for aesthetic purposes.

All roundabouts shall be designed and constructed in accordance with the City of Seward Standard Specifications for Municipal Construction and on details shown on the Seward Standard Plans.

Abutting properties shall not be permitted direct access to the roundabout. The center line of driveways shall be no closer than 100 feet to the inscribed circle diameter. Mailboxes shall not be installed within 40 feet from the nose of the splitter island.

Successive roundabouts shall be a minimum of 900 feet apart as measured from center to center.

(e)

Differential design speed of the various geometric elements of a roundabout shall be minimized.

(f)

The design vehicle for all roundabouts shall not be smaller than WB-40. The design vehicle for roundabouts on collector and arterial streets shall not be smaller than WB-50. The reviewing agencies may require roundabouts to accommodate larger design vehicles based on the projected traffic.

(g)

The center line of all approach legs shall pass through the center of the inscribed circle. In exceptional circumstances, a slight offset of an approach leg alignment to the left of the inscribed circle center may be granted by the City Engineer for the purposes of enhancing the entry curvature to improve flow. Under no circumstances shall the alignment of an approach leg be offset to the right.

(h)

For roundabouts with four or five approach legs, the angles between approach legs shall be equal (90° for four approach legs, 72° for five approach legs), unless limited by topography, existing street alignments, or other clearly defined constraints. In exceptional circumstances, the City Engineer may permit unequal angles between approach legs, but in such circumstances shall be as equal as possible. Under no circumstances shall the angle between any two adjacent approach legs be less than 70°.

(i)

The inscribed circle of single-lane roundabouts shall have a minimum diameter of 110 feet. The inscribed circle of dual-lane roundabouts shall have a minimum diameter of 150 feet.

(j)

The entry width for single-lane roundabouts shall be a minimum of 14 feet. The difference in width between the travel lane of the approaching street and the roundabout entry shall be accomplished with a flare. The start of the flare shall be a minimum of 80 feet before the point perpendicular to the junction of the entry curve and the circulatory roadway.

(k)

Single-lane roundabouts shall have a minimum circulatory lane width of 14 feet. Dual-lane roundabouts shall have a minimum circulatory lane width of 32 feet.

(l)

Concrete curbs shall be installed on both sides of the approach legs, along the entire outer circle and inner circle, and completely around all splitter islands. The inside circle, outer circle, and splitter islands shall each have a truck apron of a minimum width of four feet behind a mountable curb.

(m)

Obstructions are prohibited within the sight triangles developed for the stopping and intersection sight distances to the crosswalk on approach, to the yield line on approach, the circulatory lanes, and to the crosswalk on exit. Stopping sight distances shall be measured along the travel lane curvature. Sight lines shall be straight.

(n)

The public right-of-way shall extend no less than 17 feet from the outside curb of the roundabout.

(o)

Pedestrian crossings shall be provided at each approach leg to complete the pedestrian circulation system. The approach sidewalk pavement width shall be eight feet and shall be located directly across from and align with the pedestrian walkway in the splitter island.

(p)

The splitter island shall be a minimum of 50 feet in length. Where pedestrian crossings are provided, the island shall be subdivided into two islands separated by a ten-foot-wide pedestrian walkway a minimum of 25 feet from the inscribed circle. The pedestrian walkway shall match the street pavement elevation to avoid a ramp, shall include a transverse slope of 2.0% (one inch in four feet) in both directions from the center line of the island, and shall include an ADA-compliant detectable warning panel on both match lines with the street pavement.

(q)

Where a curvilinear street intersects a roundabout, a straight tangent section shall be required at the approach to the intersection. The length of this straight tangent section is dependent upon the radius of curvature. The minimum straight tangent lengths are set forth in Table 40F.

(r)

Parking shall be prohibited within the roundabout and within all approach legs. Parking shall be not intersect the stopping sight area developed from the approach sight distance. Parking shall not encroach on the approach or exit travel lanes. Under no circumstances shall parking be permitted within 20 feet from the nose of the splitter island.

(s)

Landscaping is prohibited on the splitter islands of single-lane roundabouts. Landscaping on splitter islands for dual-lane roundabouts shall not interfere with stopping or intersection sight distances and is prohibited from areas within the sight triangles.

(t)

The center island shall be landscaped using approved plant materials and shall include three deciduous and two evergreen trees of an approved species with a minimum caliper size of two inches. Trees shall have a mature width that does not exceed 25 feet. Deciduous tree selection shall be derived from the list of approved street tree species, and evergreen tree selection shall be derived from the list of approved business park tree species, both lists maintained by the City Tree Board. Landscape maintenance and replacement shall be the responsibility of the abutting property owners, a homeowners' association, or other private entity. A landscape plan shall be submitted for approval by the reviewing agencies. All landscape materials to complete the approved landscape plan shall be installed within one calendar year from the completion of paving of the roundabout.

[1]

All areas of the center island within the sight triangles shall be landscaped with low-growing, mowable turf grass. All landscaping within six feet of the center island curb shall be low-growing, mowable turf grass. Areas within the perimeter established rotating the tangents of the intersection sight triangles are not subject to sight distance requirements.

[2]

Center islands shall be provided with an irrigation system.

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 urban subdivisions shall not exceed 600 feet in length, unless necessitated by exceptional topography or other demonstrable constraints. Blocks within rural subdivisions shall not exceed 1,320 feet. Exceptions to the length requirement shall be approved with the unanimous consent of the reviewing agencies.

Blocks without an outlet greater than 150 feet require a turnaround in the form of a cul-de-sac or temporary turnaround as measured from the point of intersection to the edge of pavement.

(8)

Culs-de-sac.

Cul-de-sac streets designed to have one end permanently closed shall not exceed 600 feet in length and shall be designed so that vision from entrance to end is not restricted. A longer length is permissible within conservation developments or in the case of unconventional developments, such as golf course subdivisions. Exceptions to the length requirement shall be approved with the unanimous consent of the reviewing agencies.

The closed end of a cul-de-sac shall have a turnaround of sufficient diameter to accommodate the turning radii of a WB-40 design vehicle. Minimum diameters are set forth in Table 40B. This diameter may be increased by the reviewing agencies if deemed necessary in the case of a commercial or industrial subdivision. In very low density subdivisions, the reviewing agencies may allow the use of hammerhead designs or other nonstandard designs.

Culs-de-sac shall not intersect a major or minor arterial.

(9)

Specific design standards are established by the City of Seward's Subdivision Design Manual and the Seward Standard Plans.

Cartway access.

Local streets. Each parcel shall be allowed one private driveway onto the adjacent local street. There shall be a minimum 15 feet of separation from the edge of a driveway throat to edge of the adjacent driveway throat.

Collector streets. Each parcel shall be allowed one private driveway onto the adjacent collector street. There shall be a minimum 50 feet of separation between the center lines of two adjacent driveways.

Minor arterial streets. Each parcel shall be allowed one private driveway onto the adjacent local street. There shall be a minimum 100 feet of separation between the center lines of two adjacent driveways.

Major arterial streets. Driveways or access from adjacent properties shall not be allowed onto the adjacent major arterial street.

Roundabouts. The center line of driveways shall be no closer than 100 feet to the inscribed circle diameter of the roundabout.

Highways. All access to an adjacent state highway shall be controlled by the Nebraska Department of Transportation (NDOT).

Exceptions to the access requirements for local, collector, and arterial streets shall be approved with the unanimous consent of the reviewing agencies.

Horizontal clear zone.

Cartways shall have a horizontal clear zone free of nonshielded obstacles. Exceptions include traffic control devices, railroad signals, railroad tracks, bridges and bridge rails, ditches, drainage inlets, drainage flumes, culverts, driveways, intersections, bikeways and shared-use paths, earth dikes, curbs, raised islands, guardrails, median barriers, crash cushions, concrete barriers, barrier curb, parking meters, and mailboxes. Roadway light poles in the horizontal clear zone shall have frangible bases to provide a breakaway feature.

Minimum lateral obstacle clearance for curbed sections shall be two feet as measured from the back of the curb to the face of the obstacle or six feet as measured from the edge of the traveled way to the face of the obstacle, whichever is greater.

Minimum lateral obstacle clearance for noncurbed sections shall be eight feet as measured from the edge of the traveled way to the face of the obstacle.

§ 410-40.4 Utilities.

Electric.

Electric power lines shall be provided by underground wiring within easements or public rights-of-way, except where, in the opinion of the reviewing agencies, such location is not feasible. Poles for permitted overhead lines shall be placed in rear lot line easements; or in other locations designed to reduce their visual impact.

New lots adjacent to existing overhead service may utilize that service; however, new local service connections shall be underground.

Year-round screening of any aboveground utility apparatus is required. Screening shall be consistent with the landscape and screening standards set forth in Article 33 of this chapter.

Communications.

All telephone, television, copper wire, coaxial cable, fiber-optic cable and other communication lines shall be provided by underground wiring within easements or public rights-of-way, except where, in the opinion of the reviewing agencies, such location is not feasible. Poles for permitted overhead lines shall be placed in rear lot line easements; or in other locations designed to reduce their visual impact.

New lots adjacent to existing overhead service may utilize that service; however, new local service connections shall be underground.