(A) Roadway design and technical criteria. This section sets forth the minimum design and technical criteria to be used in the preparation of all roadway plans. All roadway plans should be designed in conformance with these standards, the Americans with Disabilities Act (ADA), being 42 U.S.C. §§ 12101 et seq.
(B) Typical section. Street typical sections and right-of-way will be provided as shown on the standard drawings for local road, minor collector and major collector. The typical section for arterial streets will be designed based on site specific information and parameters associated with the corridor. At a minimum, minor arterial typical sections will include 11-foot driving lanes, eight-foot boulevards and six-foot sidewalks. At a minimum, major arterial typical sections will include 12-foot driving lanes, ten-foot boulevards and six-foot sidewalks. All sidewalks will be concrete.
(C) Drive approach standards; curb cut requirements. Driveways along public and private roadways shall comply with city standard drawing. The purpose of these standards and requirements is to regulate and control the location, size, type, construction, maintenance and quantity of curb cuts, driveway aprons and sidewalk driveway crossings in the city from the standpoint of proper design, safe and efficient entry to and exit from city streets to private property, safety of vehicular traffic in the streets, and safety of pedestrian traffic on the sidewalk area.
(D) Horizontal alignment. Good engineering design uses minimum and maximum design criteria only when site constraints prohibit otherwise.
(1) Turning radius. All roadways shall intersect at right angles as nearly as possible, with no roadways intersecting at an angle less than 75°.
(2) Curb return radius. Minimum curb returns shall be as shown in Table 5-1. Larger radii may be permitted based on land use and engineering analysis.
(3) Design speed. Design speed shall be as shown in Table 5.2. The design speed is typically higher than or equal to the posted speed limit. The design speed determines various geometric design features of roadways.
(4) Horizontal curves. The minimum centerline radius for horizontal curves shall be as shown in Table 5.2.
Table 5-1. Curb Return Radius at Intersections*
| |
Street Classification | Radius in Feet(1) |
Arterial | ** |
Local | 10 |
Major collector | 15 |
Minor collector | 15 |
* Measured from back of curb ** Per AASHTO standards or approved engineering analysis (1) Minimum radius, may be larger based on engineering justification. | |
(5) Meeting streets. Two streets meeting a third street from opposite sides shall meet at the same point, or their centerlines shall be off-set at least 125 feet.
(6) Super elevation. Super elevation may be required for collector and arterial streets based upon design speed and horizontal geometry. Super elevation shall be in accordance with the recommendations of AASHTO or other engineering guideline widely accepted by the engineering community.
(7) Spiral curves. Spiral curves shall not be used on roadways within the city (state highways excluded).
(8) Barricades. Wherever roadways terminate due to project phasing, subdivision boundaries and the like barricades are required in accordance with the Manual of Uniform Traffic Control Devices (MUTCD).
Table 5-2. Street Design Standards/Criteria
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Design/Standard Criteria | Street Type | |||
Arterial | Collector Ordinary | Local | ||
Major | Minor | |||
Table 5-2. Street Design Standards/Criteria
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Design/Standard Criteria | Street Type | |||
Arterial | Collector Ordinary | Local | ||
Major | Minor | |||
Angle at intersection centerline (maximum) | ** | 85° | 75° | 75° |
Centerline radius on curves (minimum) | ** | 250' | 200' | 100' |
Cul-de-sac length | NA | NA | NA | 600' |
K Factor (minimum) | (1) | (1) | (1) | (1) |
Length of tangent at intersection | ** | 150' | 100' | 75' |
Maximum grade | 6% | 8% | 10% | 12% |
Maximum grade within 75' of intersection centerline | ** | 3% | 4% | 5% |
Minimum grade | ** | 0.5% | 0.5% | 0.5% |
Minimum design speed (mph) | 40 | 35 | 25 | 20 |
Standard street crown | 2% | 3% | 3% | 3% |
Stopping sight distance (minimum) | (1) | (1) | (1) | (1) |
Tangent length between reverse curves | ** | 150' | 100' | 50' |
Vertical curve required when algebraic difference in grade greater than | 1% | 1% | 1.5% | 2% |
** All design criteria per AASHTO standards (1) Per AASHTO based on design speed | ||||
(E) Vertical alignment. Good engineering practice does not utilize minimum and maximum design criteria unless site constraints dictate otherwise.
(1) Changing grades. Continuous grade changes or “roller-coastering” is not desirable in most cases and will not be allowed, unless justified site conditions and sound engineering judgement. The limitation of grade breaks in lieu of vertical curves is identified in Table 5-2.
(2) Vertical curves. All vertical curves shall be symmetrical. Design criteria for vertical curves are found in Table 5-2.
(3) Intersections. The following additional criteria shall apply at intersections.
(a) The grade of the “through” street shall take precedence at intersections. At intersections of roadways with the same classifications, the more important roadway, as determined by the PWD, shall have this precedence. Side streets shall be warped to match through streets within maximum grade identified in Table 5-2.
(b) The elevation at the point of tangency (PT) of the curb return on the through street is always set by the grade of the through street in conjunction with normal pavement cross slope. Carrying the crown of the side street into the intersecting through street is not permitted. At an arterial-arterial intersection, a more detailed review on the entire intersection’s grades and geometrics shall be performed by the designer and submitted for review and approval.
(4) Curb and gutter. Minimum grade for all curb and gutter is 0.4%.
(5) Connection with existing roadways. Connections with existing roadways shall be smooth transitions conforming to normal vertical curve criteria if the algebraic difference in grade (A) between the existing and proposed grade exceeds the difference identified in Table 5-2. When a vertical curve is used to make this transition, it shall be fully accomplished prior to the connection with the existing improvement. Field-verified slope and elevation of existing roadways shall be shown on the plans.
(F) Roadway drainage.
(1) Generally. Drainage systems shall be designed in accordance with §§ 11.06.040.010 through 11.06.040.070. Development plans, including a drainage report, for the drainage system are required for concurrent review with, and shall be considered a part thereof, of the roadway design.
(2) Inlets. Inlets shall be located to intercept the major curb flow at the point curb flow capacity is exceeded by the storm run-off. Inlets should be aligned with lot lines wherever possible. Inlets shall also be installed to intercept cross-pavement flows at points of transition in super elevation. Due to the presence of pedestrian ramps, inlets are not allowed in the curb return, but will be located at the tangent points of the curb return.
(3) Cross slope. Except at intersections, or where super-elevation is required, roadways shall be level from top of curb to top of curb and shall have a crown cross-slope as identified in Table 5-2. Parabolic or curve crowns are not allowed. Maximum pavement cross slope allowed is 5% at intersection transitions. In no case shall the pavement cross slope at warped intersections exceed the grade of the through street. When warping side streets at intersections, the crown transition should be completed within 75 feet horizontally for local streets, 100 feet horizontally for collector streets and 150 feet horizontally for arterial streets.
(G) Roadway specifications.
(1) Pavement thickness. Pavement thickness design must be completed for all new or reconstructed roadways and shall be based on the current AASHTO Guide for Design of Pavement Structures, or the current Asphalt Institute Manual Series No. 1 (MS-1) for thickness design. The pavement design report, based upon specific site soil data and design year traffic loading conditions, shall be prepared by a professional engineer and submitted to the PWD, along with the plans and specifications for the project. The design shall be based on at least a 20-year performance period traffic volume; however, the minimum design lane 18,000-pound equivalent single axle load (ESAL) used in the pavement design shall not be less than 50,000-pound ESAL. The minimum asphalt pavement thickness for any new street or roadway shall be three inches and minimum of eight inches of crushed base course will be provided.
(2) Utility trenches. Utility trenches, which include water and sewer services, cut through asphalt newer than ten years shall be saw cut the entire width of the street and backfilled with flowable fill material, complying with the requirements of flowable fill contained in the MPWSS. The intent is to protect the integrity of the roadway riding surface and eliminate the potential for roadway failure due to failure of trench backfill material under a roadway.
(3) Application. Prior to any street opening, an application with a traffic-control plan shall be submitted to the City PWD for review and approval. All street openings shall be for a maximum of 24 hours, unless there is written approval from the PWD. On collector or higher classified streets, the street opening will be limited to 8:30 a.m. to 4:30 p.m. If a multi-day closure is required, the trench shall be covered and protected to provide vehicular traffic. All street patches will provide a minimum eight inches of crushed base course and three inches of asphalt concrete pavement. Match existing CBC and ACP depths if greater than the minimum.
(4) Temporary patches. For temporary patches, when hot mix asphalt is not available, shall be a minimum of six inches of compacted road mix. Cold mix asphalt can be used on a case-by-case basis as approved by the PWD. All temporary patches shall be replaced with hot mix asphalt as soon as hot mix asphalt pavement is available but no later than June 1.
(5) Tunneling. No tunneling under sidewalks, curb and gutter will be allowed. If the excavation extends under the curb, gutter and sidewalk, the curb, gutter or sidewalk shall be removed at the closest joint past the extent of the trench.
(6) Utility trenches. All utility trenches, including the curb, gutter and sidewalk, shall be warranted by the person or contractor requesting the street opening for two years after acceptance by the Public Works Department of the completed restoration to all portions of the right-of-way disturbed by the opening, including the road surface, curb and gutter, and sidewalk, and the proper disposal of all waste material.
(H) Monumentation. Monuments in monument boxes shall be provided in new or reconstructed streets at all section corners, quarter corners, and sixteenth corners.
(I) Traffic calming. TRAFFIC CALMING is defined as a combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior and improve conditions for non-motorized street users. In simple terms, traffic calming techniques are typically aimed at maintaining 85% percentile vehicle speed at or below the posted speed limit. If applied properly, these techniques result in a safe and pleasant environment for pedestrians and bicyclists. Traffic calming applied to roadway designs for new development should be evaluated on a case-by-case basis and if utilized, should be appropriate for the intended function of each street or street segment. Streets designed to function as part of the major street system should be designed primarily to move traffic in an efficient, convenient and safe manner. Local streets and residential collectors should be designed to provide access to properties while discouraging through-traffic and higher travel speeds that often accompany it. New street designs and developments should consider traffic calming strategies to reinforce the appropriate functions of the designed streets. These would include layout and connectivity of street systems and pedestrian/bicycle facilities, intersection treatments, and basic design standards for width, curvature, parking, and landscaping.
(J) Utility corridors within new subdivisions or undeveloped annexations.
(1) All new utility installations within the public right-of-way requires written approval from the PWD prior to installation, so as to assure that the new utilities do not incommode or endanger the public in the use of the street in accordance with MCA § 69-4-101.
(2) All new utilities shall be placed underground except where underground installation is not feasible as defined in MCA § 69-4-102(2). Transformers and junction boxes may be installed above ground in locations approved by the PWD. All new underground utilities installed parallel to city-owned utilities within the public street right-of-way shall be located horizontally at least five feet away from the city-owned utilities. If five feet cannot be maintained, the utility must submit a deviation request to the PWD.
(3) Utilities shall not be installed in street boulevards, except above ground features, such as light poles, residential transformers, and secondary pedestals, along with the associated wiring for these features, may be allowed providing that the placement of these features will not interfere with the planting, growth and care of boulevard trees or impede traffic sight distance. Perpendicular crossings of the boulevard may be allowed if placed in such a manner not to prohibit the planting of boulevard. All utilities that are less the four and one-half feet in depth are encouraged to be installed in protective conduit, whenever possible. The protective conduit will allow for the maintenance and replacement of the utility without damaging any boulevard trees. All utilities shall be installed at the required depth relative to the finished grade of the finished surface.
(4) As part of any subdivision or development involving the extension of city utilities, the developer shall provide engineered plans for all utilities, including gas, power, phone, fiber and the like on the infrastructure plans for review and approval. All applicable laws, rules and regulations of appropriate regulatory authority having jurisdiction over such facilities shall be observed.
(K) Traffic impact studies.
(1) Private or public developments which contribute 200 or more vehicle trips per day to the city street system shall have a traffic impact study completed by an engineer with adequate experience and expertise in transportation engineering. Such study shall indicate the expected increase in traffic movements on the existing roadways serving the development and shall determine existing conditions on roadways to be impacted by the development.
(2) The traffic impact study should present an objective technical analysis in a straightforward and logical manner that leads the reviewer through the analytical process to the resulting conclusions and recommendations. Sufficient detail should be provided so that the reviewer is able to follow the path and methodology of the study. All assumptions should be clearly documented with published sources referenced as necessary. All traffic impact studies shall be signed and stamped by a licensed professional engineer registered in the state.
(3) At a minimum, the traffic impact study should include the following information.
(a) Introduction. Provide an introduction with an overview and discussion of the development proposal. Include a vicinity map detailing the property location, area of analysis, a conceptual site plan reflecting the boundaries of the development, and information detailing the designated zoning and physical features of the site and surrounding area.
(b) Existing conditions. Include a discussion about the existing transportation network, roadway geometrics, traffic data collection, crash analysis, existing level of service (LOS) and existing roadway capacity analysis. Also include a discussion about nearby land developments and known transportation improvements.
(c) Future conditions. Discuss the future transportation conditions for the anticipated date of project completion. Include ambient background traffic growth and anticipated future developments.
(d) Proposed condition. Discuss the proposed development characteristics and determine the number of anticipated trips and traffic distribution expected to occur as a result of the development. Provide a trip generation analysis to determine traffic attributable to the development using the most recent Institute of Transportation Engineering (ITE) Trip Generation Manual. Determine trip distribution and assignment to the roadway network using standard engineering practice and methodology contained in the ITE Trip Generation Manual. Assess the traffic impacts attributable to the development using the results from the trip generation and. Evaluate intersection LOS and roadway capacity analysis.
(e) Recommendations. Provide recommendations to remedy deficiencies in the transportation network caused by impacts from the development. These recommendations shall include the engineer’s recommended location, nature and extent of proposed transportation improvements, including bike and pedestrians associated with the development to ensure safe and efficient roadway operations and capacity, and compatibility with city standards and goals of the Greater City of Deer Lodge Area Transportation Plan.
(f) Conclusion. Include a conclusion that provides a clear and concise description of the study findings and engineer’s recommendations.
(L) Signing and pavement marking requirements.
(1) Street identification signs shall be installed at all new intersections in accordance with the Montana Public Works Standard Specifications (MPWSS), latest edition. All regulatory traffic-control signs will be completed in accordance with the MUTCD. Stop signs shall be installed on local streets when they intersect with any collector or arterial streets.
(2) All pavement markings shall be inlaid thermoplastic for all crosswalks, stop bars, words and symbols. Roadway centerlines, bike lanes and outside lane lines shall be epoxy paint. All pavement markings and reflective glass beads will be constructed in accordance with MPWSS.
(3) Crosswalk markings should not be used indiscriminately. An engineering study should be performed before crosswalks are installed at locations away from traffic signals or stop signs. Mid-block crosswalks are discouraged.
(M) Sidewalks. All sidewalk replacement or new sidewalk installation will be constructed in accordance with MPWSS.
(Prior Code, § 11.05.050.020) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)