5.1 General Information
The design of improvements on the state highway shall conform to current SHA standards, specifications, and accepted engineering practices. Due to the breadth and complexity of highway engineering practice, a comprehensive treatment of the subject is not possible within this manual. This chapter, however, is intended as a starting point and reference on design policies and procedures commonly applicable to access-related improvements. The tables and design guidance presented in this chapter are derived from design practices that were current at the time the manual was published. The applicant and/or their professional representative is responsible for seeking out updated standards, policies, and practices for reference in designing access-related improvements along with all design criteria SHA has adopted as policy. In presenting certain requirements, reference is made to Type I, Type II and Type III projects, which are found under Supplemental Design Guidance.
5.2 Standards and Specifications
5.2.2 Construction and Materials Specifications – All construction on the state highway right-of-way shall conform to the latest version of MDOT SHA’s Standard Specifications for Construction and Materials, including all applicable Supplemental Specifications and Provisions.
5.3 Geometric Layout of Improvements
The horizontal and vertical geometric layout for site access improvements and highway infrastructure improvements shall be established in accordance with the following requirements.
5.3.2 Site Access Improvements – The layout of deceleration lanes, acceleration lanes, bypass lanes, left-turn lanes, and other routine site access improvements shall conform to the requirements outlined in Chapter 3 Street Connection Standards. Alternate designs based on accepted engineering practices may be approved on a case-by-case basis, with appropriate justification and supporting documentation, for use where the standard designs are not feasible.
5.3.3 Highway Infrastructure Improvements – The layout of highway infrastructure improvements shall conform to the requirements outlined in Chapter 4 Site Access Improvements, together with the latest version of the AASHTO policies referenced in 5.2 Standards and Specifications above, all relevant MDOT SHA design policy, and accepted engineering practice. Where the intersection includes a county or municipal road, the requirements of the local jurisdiction may also apply at their discretion. The geometric layout of site access improvements proposed within the limits of a highway infrastructure improvement shall conform to the requirements of Chapter 4 Site Access Improvements.
5.4 Highway Alignment
Where a new or modified horizontal and/or vertical alignment is proposed for a state highway, the alignment shall conform to AASHTO policy and pertinent MDOT SHA practices. Developing safe and appropriate alignments for new highways is a complex engineering endeavor which requires proper application of many technical criteria. The following sections outline basic design parameters applicable to alignment modifications that are necessary to accommodate the proposed site access, support new lane allocations, or correct sight distance deficiencies. A change in the horizontal or vertical curvature of the highway centerline and/or through-lanes is considered an alignment modification. For purposes of this manual, a tapered lane shift conforming to the MUTCD is not considered an alignment modification.
5.4.2 Horizontal Curves – New alignments and horizontal curve modifications shall be designed to provide proper sight distance and handling characteristics for the design speed in accordance with AASHTO policy. The curvature and associated superelevation rates and transitions shall be appropriate for the design speed, route function, and geometric characteristics.
Maximum superelevation rates for the design of state highways, in accordance with SHA design practices, are given in Table 5.4.2. Use of a consistent emax for the design of successive curves along a route yields predictable handling characteristics and steering efforts as drivers negotiate curves of different radii. For this reason, it is important that retrofitted curve modifications be consistent with the superelevation characteristics of the existing highway.
Table 5.4.2 Maximum Superelevation Rates
For simple curves, two-thirds of the superelevation transition length shall be located on the tangents beyond the horizontal curve, while one-third shall be located within the horizontal curve. The use of spiral or compound curves is reserved for select expressways and is not covered in this manual.
5.4.4 Profile Grades – Profile grades for new or modified state highways shall be determined in accordance with AASHTO policy. Maximum grades shall be appropriate for the context and function of the state route, addressing the needs of bicycle and pedestrian users as well as motor vehicle traffic.
5.5 Pavement Cross Slope
Proper pavement cross slope is necessary to provide acceptable vehicle traction, handling characteristics, and pavement drainage along curved highway alignments. The criteria of this section apply to any widening, reconstruction, or resurfacing of the existing highway associated with or affected by the improvements.
Table 5.5 Maximum Rollover Standards
For purposes of applying these standards, auxiliary lanes such as acceleration lanes, deceleration lanes, and bypass lanes, are considered travel lanes rather than shoulders. When existing shoulders are improved to function as auxiliary lanes, it is typically necessary to adjust the existing pavement cross slope. On the high side of a superelevated section (along the outside of the horizontal curve), existing shoulders typically must be removed and replaced with new paving that slopes in the same direction as the adjacent through lane.
5.6 Lane and Shoulder Widths
Lane and shoulder widths are based on facility type, traffic volumes, and speed, and shall meet AASHTO policy and be approved by the relevant MDOT SHA District Traffic Office. Shoulder widths must also address bicycle compatibility as outlined in the MDOT SHA Bicycle Policy and Design Guidance. In no case shall an existing facility be negatively impacted below required design standards.
5.6.2 Through-Lane Widths – Standard widths for through-lanes on state highways shall comply with AASHTO standards and the following MDOT SHA guidelines. Reduction of through-lane widths to below these standards in order to accommodate proposed traffic patterns and lane configurations is not acceptable.
Table 5.6.3 Width of Through Lanes Along State Highways
5.6.3 Width of Left Turn Lanes and Center Turn Lanes
5.6.4 Bypass Lanes
5.6.5 Bicycle Accommodations – MDOT SHA has developed design guidelines for the preferred accommodations to benefit bicycling along state highways. It is MDOT SHA’s goal to provide the preferred accommodations as part of all roadway projects where feasible and reasonable. Providing bicycle accommodations is especially important where the existing or proposed land use supports cycling. This includes trip generators and destinations such as employment, education, residential, commercial, recreation, and transit centers. While it is MDOT SHA’s intent to provide the preferred accommodations on all projects, it is understood that project and applicant requests for waiver of required bicycle and pedestrian facilities will be considered on a case by case basis. All waiver requests will be subject to written submittal and approval of a design waiver exception.
5.7 Roadway Excavation and Slope Grading
5.7.2 Cut Slopes
5.7.3 Fill Slopes – Fill slopes shall be graded as flat as possible within the state right-of-way and extending, where feasible and reasonable. Fill slopes steeper than 4:1 but no steeper than 3:1 are considered traversable but non-recoverable. As such, these slopes shall not be included in the calculation of available clear zone width however they may be acceptable if the remainder of the design clear zone (subtracting the width available at the top of the slope, but a minimum of 10’) is available at 6:1 or flatter beyond the toe of the 3:1 slope. Fill slopes steeper than 3:1 are considered critical.
5.7.4 Roadside Grading – Grading along roadside areas, median and outside, shall be designed in accordance with the principles established in the AASHTO Roadside Design Guide (RDG) and the SHA Guidelines for Traffic Barrier Placement and End Treatment Design to promote a safe vehicular recovery area wherever feasible and reasonable, as determined by the SHA.
Paving for access improvements and highway infrastructure projects shall conform to the requirements of this section. These requirements are subject to change as refinements in technical standards and industry practices occur. SHA staff will furnish the latest approved pavement sections and mix designations upon request. Some projects require design approval from the MDOT SHA Office of Materials Technology.
5.8.2 Full Depth Pavement Sections – Full-depth paving shall conform to the sections and specifications identified in the Access Permit. The type and depth of full-depth pavement sections specified, and the process by which the appropriate pavement sections are determined, will vary depending on the magnitude of the improvements under permit, the functional classification of the state highway, actual or projected traffic volumes, the anticipated service of the improvements, site conditions, pending maintenance projects, and other factors. The process and requirements are discussed below.
The standard pavement sections for routine projects are given in Appendix D Paving Specifications. These are broken down into Light Duty, Moderate Duty, and Heavy Duty for use on different types of highways with different traffic conditions. These sections are subject to periodic update by OMT.
It should be noted that the developer/engineer has the option of performing a more detailed pavement investigation following the Major Project’s criteria and requirements at their own cost. If the results of their investigation indicate that OMT’s recommendations are over-conservative for the site conditions, the report of their investigation should be submitted to OMT for further review and re-evaluation of the pavement recommendations.
For detailed information, please refer to OMT’s guidelines.
If the existing shoulder is determined to be traffic-bearing, it may need to be built up with additional layers of pavement to establish a proper cross slope. The existing shoulder shall be milled or carbide ground, wedge/leveled, and overlaid to the required cross slope. Refer to the details in Standard Road Widening and Paving Details. At least the outermost 1’ of existing shoulder, measured towards the travel lane from the edge of pavement, shall be saw-cut and removed to provide a clean joint in solid material at the edge of the widening.
5.8.5 Minimum Width of Full-Depth Paving – Full-depth pavement construction shall be at least 4’ wide at all points along the proposed widening and/or pavement replacement. This is to facilitate proper subgrade preparation, compaction, and pavement placement. Where this is not possible, concrete Mix 7 or Mix 9 may be substituted for the asphalt base for sections provided in Standard Road Widening and Paving Details.
5.8.6 Cross Slope Transitions at the Limits of Improvements – Where there are existing paved shoulders at the limits of the improved typical section, a gradual cross-slope transition shall be accomplished. The transition area shall be located on the first 50’ of shoulder beyond the limits of the improved typical section, unless specifically noted otherwise on the plans. The transition area shall be paved with the specified full depth pavement section or milled, wedge/leveled, and overlaid. Refer to the details in Standard Road Widening and Paving Details.
5.8.7 At-Grade Resurfacing for New Pavement Markings – At-grade resurfacing involves carbide-grinding or milling the existing pavement to a depth equal to the desired surface course thickness and overlaying with an approved surface course.
5.8.8 Overlay for New Pavement Markings – Where it would not result in unacceptable curb reveal, drainage conditions, or grade tie-ins, an overlay may be placed over existing pavement without milling or grinding except at transition areas, at the discretion of MDOT SHA.
5.8.9 Pavement Patching – The following guidelines apply to patching required to address substantially increased traffic volumes or to repair pavement damaged during construction.
5.9 Curb-and-Gutter, Medians, and Traffic Control Islands
Curb-and-gutter, medians, and traffic control islands shall conform to the following guidelines.
5.9.2 Curb-and-Gutter – Curb-and-gutter all consist of Standard Concrete Combination Curb-and-Gutter Type ‘A’ or Type ‘C’ (conforming to MDOT SHA Book of Standards for Highway & Incidental Structures No. MD-620.02 with a 1’-0” wide gutter pan). All curbs shall have a minimum of 3 ½’ compacted earth backing for support, sloping up 1/2" per foot from top of curb for a minimum of 3 ½’. The area between/behind the curbs shall be graded and sodded or seeded, or paved. All curbs shall be nosed down at their limits. The transition to different on-site curb-and-gutter shall be made outside of state right-of-way. Depressed curb entrances shall be constructed in accordance with the MDOT SHA standard details. The apron shall be poured separately from the-curb and-gutter.
5.9.3 Traffic Control Islands – Geometric design of islands shall conform to AASHTO policy, MDOT SHA standards, and accepted engineering practice. Non-standard layout may be required as necessary to control unpermitted site ingress or egress however the design must be acceptable to MDOT SHA. Islands shall be constructed of Standard Concrete Combination Curb and Gutter Type “A”, Type “B”, or Type ‘C’ and paved with 5" Concrete Sidewalk (referring to a standard paving practice) using MDOT SHA Concrete Mix No. 2 on a properly-prepared subgrade. The sidewalk shall be scored in 5’ blocks. The sidewalk grade shall meet the top of the roadside curb. The leading edge of an island using Type 'A' curb-and-gutter shall be nosed down for the first 4’ and set back a minimum of 3 ½’ from the edge of the travel lane. Positive drainage shall be provided across the surface of the island. If the enclosed area of the interior field of the island exceeds 250 square feet, turfgrass may be acceptable instead of concrete sidewalk.
5.9.4 Medians – Median geometric design shall conform to AASHTO policy and accepted engineering practice. The construction requirements for medians vary with the width of the median and the application.
5.10 Drainage/Hydraulic/Hydrologic Requirements
Approval from the MDOT SHA Highway Hydraulics Division is required for all projects that will affect state highway drainage conditions or facilities. Refer to the Hydraulic/Hydrologic Guidelines for information on the requirements for review and approval.
Any structures, other than standard storm drainage, sign support, traffic signal equipment, and lighting structures, shall be reviewed and approved by the MDOT SHA Bridge Design Division. Preliminary coordination is important to ensure designs are consistent with MDOT SHA requirements and allow time for the development of maintenance agreements.
The review and approval of structures within or impacting MDOT SHA right-of-way require several plan review submissions including Type, Size, and Location (TS&L), Foundation, and Structural Review. In special cases, upon approval from the MDOT SHA Bridge Design Division, the TS&L and Foundation Review may be combined.
5.11.2 Retaining Walls – The design plans for proposed retaining walls within the state's right-of-way or easement, or those on private property, which provide structural support of the state highway embankments, shall be reviewed and approved by the MDOT SHA Bridge Design Division. Plans should be submitted at appropriate review intervals (TS&L, Foundation, and Structural) throughout the design development process for comments and guidance. Minimum information must be shown on the plans at each stage of design progress in order to facilitate review.
Retaining walls meant for site grading purposes shall not be located on the state's right-of-way. Such walls shall be located entirely on private property, including all tiebacks, soil anchorages, etc. Retaining walls meant for construction of the required state highway improvements will be considered on a case-by-case basis. Applicants shall thoroughly evaluate alternatives before proposing retaining walls on state property. Cross sections must be provided with retaining wall plans to show the location of the retaining wall. Ornamental landscape walls that do not provide slope support are subject to review and approval by the relevant MDOT SHA District Office.
5.11.3 Small Structures (Culverts) – The design plans for culverts with a span of 60" or more shall be reviewed and approved by the MDOT SHA Office of Bridge Development's Bridge Design Division. Submission of a hydrologic/hydraulic study may also be required for review and approval by the MDOT SHA Structure Hydrology and Hydraulics Section. Plans should be submitted at appropriate review intervals (TS&L, Foundation, and Structural) throughout the design development process for comments and guidance. Minimum information must be shown on the plans at each stage of design progress in order to facilitate review.
5.11.4 Special or Non-Standard Drainage Structures – Special or non-standard drainage structures shall be reviewed and approved by the MDOT SHA Bridge Design Division when this requirement is identified by the MDOT SHA Highway Hydraulics Division.
The Bridge Design Division maintains Plan Development Checklists that outline the minimum amount of information that must be included on the structure plans at each review interval. In some cases information included in the checklist is not applicable to the type of structure that is being proposed. Foundation borings are required prior to the submission of the Foundation review.
Each proposed structure should contain its own set of plan sheets within Contract Plans that are separate from the roadway plans and details.
The Plan Development Checklists are evolving documents, please send an email to email@example.com for the latest version of the checklists prior to submitting structure plans.
5.12.2 Preferred Sidewalk Facilities – Continuous 5’ wide sidewalk, free of obstructions, is preferred on both sides of all closed-section roadways as part of new construction or reconstruction when the existing or proposed land use will support walking, sidewalks are included in the local Master Plan, sidewalks are requested by the local jurisdiction, or sidewalks would serve to connect other facilities. The inclusion of sidewalk or existence of sidewalk in new construction or reconstruction should prompt the inclusion of other pedestrian amenities and benefits to promote walking as appropriate. Pedestrian benefits and amenities can include such items as wheelchair ramps, pedestrian crosswalks, pedestrian signals, and pedestrian lighting.
5.12.3 Design Requirements – All sidewalks, ramps, and pedestrian facilities shall be designed to conform to the MDOT SHA Accessibility Policy and Guidelines for Pedestrian Facilities along state highways. Requirements include, but are not limited to, the use of appropriate sidewalk ramps, widths, landings, railings, slopes, and surfaces.
5.12.4 Construction Specifications – Unless the local jurisdiction requires use of a different specification, sidewalks constructed in the state's right-of-way shall be constructed in accordance with the MDOT SHA Standard Specifications for Contruction and Materials and pertinent standard details. Sidewalk shall be scored in 5’ blocks, with expansion joints every 15’. The sidewalk grade shall meet the top of the roadside curb, then rise ¼" per foot for the total width of the sidewalk.
5.13 Environmental Compliance and Landscaping
Plans for landscape construction shall conform to approved Master Plan and MDOT SHA standards. Refer to MDOT SHA Environmental Guide for Access and District Permit Applicants and other MDOT SHA landscape guidance documents. These documents provide guidance to develop plans for landscape construction and the Engineer’s Estimate for landscape items.
Projects that involve the installation or removal of trees or areas of brush on MDOT SHA property, or which are within the 1 mile viewshed of a Scenic Byway, or which may impact adjacent natural areas on MDOT SHA property, will require review by the MDOT SHA Office of Environmental Design.
5.14 Signing and Pavement Marking
Signing and pavement markings on state highways shall conform to the Federal Highway Administration Manual on Uniform Traffic Control Devices, latest edition, and pertinent MDOT SHA standards and specifications. Depending on the complexity of the proposed improvements, formal plans and review and approval by the Assistant District Engineer - Traffic and/or SHA Traffic Engineering Design Division (TEDD) may be required.
5.14.2 Pavement Markings – Pavement markings appropriate for delineating the proposed traffic patterns associated with the proposed access and/or road improvements are required in accordance with standards and practices accepted by MDOT SHA. Selection of appropriate pavement marking materials (paint, thermoplastic, heat applied, preformed, etc.) for the specific highway and application will be made by the Assistant District Engineer - Traffic. Existing pavement markings affected by the access and/or improvements shall be removed using methods acceptable to the Assistant District Engineer - Traffic and replaced, reset, or relocated as determined during the project review process. The “Line Striping Material Selection Policy” contains further information regarding line striping material selection. This document can be obtained from MDOT SHA TEDD.
5.15 Traffic Signals
Traffic signal design shall be in accordance with latest standards, requirements, guidelines, and practices accepted by SHA. Design plans for all approved new traffic signal installations and all modifications to existing traffic signals, equipment, devices, etc. shall be reviewed and approved by MDOT SHA TEDD prior to the issuance of an Access Permit. In order for plans to be processed for review and approval, a Design Request approved by MDOT SHA OOTS must be on file. Following MDOT SHA’s conceptual approval of a traffic signal installation or modification, applicants should have their representatives coordinate the Design Request with the Assistant District Engineer - Traffic before preparing design plans. Traffic signal equipment to be owned and maintained by MDOT SHA shall be installed within MDOT SHA right-of-way.
The design of lighting system installation or modifications shall be in accordance with the latest standards, requirements, guidelines, and practices accepted by MDOT SHA. Standards for roadway lighting, fixtures, and supporting structures are available from MDOT SHA OOTS. Photometric plans, including quantitative photometric summaries, may be required to support lighting design. Lighting systems shall be designed to avoid glare problems in the adjacent highway. Plans for all new or modified lighting shall be reviewed and approved by MDOT SHA TEDD. When installation or modification of lighting is proposed, applicants should have their representatives coordinate a Design Request with the Assistant District Engineer - Traffic before preparing design plans. Roadway lighting equipment to be owned and maintained by MDOT SHA shall be installed within MDOT SHA right-of-way. Proposed lighting located outside of SHA right-of-way but adjacent to an MDOT SHA roadway may require review and approval by MDOT SHA to ensure glare problems are avoided.
5.17 Work Zone Traffic Control
Maintaining safe and proper traffic operation on the state highway and along adjacent access points is of paramount importance during construction of the improvements. Depending on the size and scope of improvements, either typical details or a detailed Traffic Control Plan will be required. Since traffic control setups and requirements can have a significant bearing on construction costs and schedules, it is important for prospective applicants to ascertain traffic control measures during the design phase of their projects.
5.17.2 Work Zone Traffic Control Plan – Extensive, prolonged, or complex construction activity on or along the traveled portion of the highway that cannot be handled using standard Work Zone Traffic Control Typical Applications shall be controlled by a site-specific Work Zone Traffic Control Plan. This formal engineering plan shall be developed by professional representatives of the applicant and submitted for review and approval by the Assistant District Engineer - Traffic prior to issuance of an Access Permit. The MDOT SHA may require a detailed work zone traffic control plan for any access permits where work is required in the traveled way or where work disrupts the normal traffic pattern.
5.17.3 Work Zone Typical Traffic Control Applications – Routine construction activity along the highway, such as shoulder work, temporary lane closures during non-peak traffic hours, and moving operations, shall be controlled using the appropriate approved MDOT SHA Standard Temporary Traffic Control Typical Applications.
5.17.4 Work Restrictions – Work within and adjacent to the traveled way, once initiated, shall be completed in successive days. All work is to be accomplished on week days only. Working hours and lane closure restrictions will be specified in the permit for each project. No work will be permitted within the roadway between the hours of 5:00 AM and 9:00 AM or 3:00 PM and 7:00 PM Monday through Friday unless prior written approval is obtained from the Assistant District Engineer - Traffic.
5.18 Clearance from Utilities
Avoiding unforeseen utility conflicts and potentially dangerous and costly impacts is an important aspect of highway as well as site design. Especially in urban areas, many underground and/or aerial utility lines may be located within the state's right-of-way.
The relocation or adjustment of any public or private utility shall be the responsibility of the Permittee. This includes traffic signals, fire hydrants, water mains, sewers, storm drains, telephone facilities, electric facilities, etc. All utility relocations necessary for construction of the permitted improvements shall be arranged and paid for by the Permittee. Utility work shall be coordinated with the MDOT SHA District Utility Engineer under a separate permit. If arrangements for utility relocations have not been finalized at the time the Access Permit is sought, the Permittee shall include the estimated cost of the utility relocations in the surety provided for the Access Permit.
Clearance from any underground or aerial utility must be acceptable to the utility owner. Minimum utility pole clearances from the highway shall be as follows, based on existing conditions or through relocations, where feasible and reasonable as determined by MDOT SHA:
Additional clearance may be required where necessary to establish or maintain an appropriate roadside clear zone in accordance with 5.7.4 Roadside Grading. The MDOT SHA Landscape Design Guide provides acceptable minimum offset distances in Chapter 5 – Utilities and in Chapter 7 – Safety, Sightlines, and Offsets.
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