Chapter 5 – Technical Design Standards
5.1 General Information
The design of improvements on the state highway shall conform to current Maryland Department of Transportation State Highway Administration (MDOT 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
5.3 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.
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5.3.1 Entrances and Street Connections – The layout of standard entrances and street connections for site and/or subdivision access shall conform to the requirements of
Chapter 1 Access Point Standards and
Chapter 2 Entrance Design Standards, respectively. The layout of street connections for collector or arterial routes shall conform to
5.3.3 Highway Infrastructure Improvements, below.
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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.
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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.
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5.4.1 Design Speed – Design speed is a selected speed used to determine the various geometric features of the roadway. The assumed design speed is a design control and should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use, and the functional classification of the highway. A design speed needs to be established based on AASHTO policy along with sound engineering judgment. Generally a design speed of 10 mph above the posted speed limit will be accepted for purposes of establishing site access improvement requirements. A lower design speed will be considered when supported by the aforementioned guidance.
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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.
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5.4.2.A. Superelevation Rate and Curve Radius – Superelevated sections are found in curves and on the transitions into and out from curves. Appropriate superelevation shall be provided or maintained for all travel lanes resulting from or affected by the alignment modifications. The AASHTO design charts shall be used to determine the superelevation to be applied on a particular curve based on the design speed, curve radius, and maximum superelevation rate (emax) established for the alignment.
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
| Application | Maximum Superelevation, emax |
|---|
| New open section facilities | .06 |
| Expressway main lines | 0.08 |
| New closed section urban facilities | 0.04 |
| Interchange loop ramps | 0.10, except 0.08 in District 6 |
| Other interchange ramps | 0.08 |
| At-grade intersections (signalized or unsignalized) | Refer to AASHTO policy |
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5.4.2.B. Superelevation Transitions – For all new roadway alignments, superelevation transitions shall comply with AASHTO maximum relative gradients. Superelevation runoff and tangent runout shall also comply with AASHTO policy including accounting for lane width, number of lanes rotated, design superelevation rate, normal cross slope rate, and maximum relative gradient. In the case where proposed improvements are matching existing roadway geometry, the following design guidance may be useful in determining transition lengths and start/end location in relation to the horizontal curve:
| Application | Rate of Change in Pavement Cross Slope per Foot of Transition Length |
|---|
| Expressways and urban highways | 0.00010 |
| Other highways | 0.00015 |
| Directional ramps and other two lane ramps | 0.00020 |
| Single lane outer ramp | 0.00030 |
| Inner loop ramps | 0.00040 |
| Transition Length = |
Full Superelevation Rate in Curve
Rate of Change in Pavement Cross Slope |
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.
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5.4.3 Vertical Curves – Vertical curves shall be designed to provide proper sight distance for the design speed in accordance with AASHTO policy, using the pertinent sight distance criteria. For retrofit widening applications, the alignment of the new pavement should match that of the existing highway unless a safety issue results.
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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.
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.
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5.6.1.A. Highway Infrastructure Improvements
- (1) Applies to improvements identified in
Highway Infrastructure Improvement Standards.
- (2) New and replacement shoulders shall comply with AASHTO standards.
- (3) Existing shoulders that are affected by the improvements but not incorporated into the improvements shall be maintained in accordance with AASHTO standards and the requirements of
5.6.5 Bicycle Accommodations. For example, a 10’ shoulder must be maintained along an improvement that displaces a portion of the existing 10’ shoulder along a high-volume, high-speed arterial route.
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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
| Application | Minimum Required Through Lane Width |
|---|
| Primary Highways | 12’ |
| Secondary Highways with a Principal Arterial functional classification | 12’ |
| All other Secondary Highways with a posted speed > 40 mph | 12’ |
| All other Secondary Highways with a posted speed of 40 mph or less | 11’ |
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5.6.3 Width of Left Turn Lanes and Center Turn Lanes
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5.6.3.A. Desirable width for left-turn lanes is 12’, required where feasible and reasonable. Minimum under any circumstances is 10’ (not including gutter pan).
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5.6.3.B. Desirable width for center-turn lanes is 14’, required where feasible and reasonable. Minimum is 12’. Normally at least one foot wider than the through-lane width.
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5.6.3.C. The median gutter pan, if applicable, is included in these widths.
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5.6.4 Bypass Lanes
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5.6.4.A. Standard bypass lanes are 12’ wide. The lane width may be reduced to 11’ in low-speed urban areas however the shoulder width may not be reduced to below design standards and must address bicycle compatibility per the SHA Bicycle Policy and Design Guidelines.
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5.6.4.B. Bypass lanes shall be open-section except along urban closed-section highways or where a curb is necessary for proper drainage.
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5.6.4.C. Further guidance on various types of bypass lanes may be obtained in the
MDOT SHA Application and Design Guidelines for Shoulder Bypass Lane (SBLs).
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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.
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5.6.5.A. Proposed Improvements – All state highway improvements shall be bicycle compatible and provide the preferred bicycle accommodations in accordance with MDOT SHA guidelines, including but not limited to
5.6.1 Highway Infrastructure Improvements and
5.6.2 Through-Lane Widths, where feasible and reasonable as determined by MDOT SHA. Further guidance on various types of bicycle accommodations may be obtained in the
MDOT SHA Bicycle Policy and Design Guidelines. If widening is being performed and full bicycle compliance can’t be provided, a Bicycle Waiver will be required. If no widening is being performed and full compliance can’t be provided, a Bicycle Compliance Certification will be required.
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5.6.5.B. Existing Conditions – Where existing conditions along the state route are capable of supporting bicycle traffic, as determined by MDOT SHA, the existing bicycle compatibility shall not be eliminated as a result of any improvements. Existing conditions that are not capable of supporting bicycle traffic, as determined by MDOT SHA, shall remain “as-is” if they are outside the limits of the improvements and are not adversely affected by the improvements. Negative impacts to bicycle accommodations will not be permitted. For further guidance, refer to the discussion on Negative Impact in the
MDOT SHA Bicycle Policy and Design Guidelines.
5.7 Roadway Excavation and Slope Grading
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5.7.1 Roadway Excavation
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5.7.1.A. Excavation for the road template shall accommodate the specified approved asphalt or Portland Cement Concrete pavement section, including the supporting base course consisting of graded aggregate or Capping Borrow material.
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5.7.1.B. The graded aggregate or Capping Borrow material shall extend underneath curb-and-gutter sections and at least 1’ beyond.
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5.7.1.C. Where unstable pavement subgrade conditions are suspected or where unsuitable subgrade material is likely to exist, additional excavation for undercut and refill may be required by MDOT SHA in order to attain specified compaction of the subgrade prior to paving. Refer to the requirements in
5.8 Paving.
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5.7.1.D. In shallow bedrock areas, if blasting method is proposed to remove the bedrock, the blasting plan shall be submitted to the MDOT SHA Office of Materials Technology for review and approval.
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5.7.2 Cut Slopes
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5.7.2.A. Cut and fill slopes shall be graded as flat as possible within the state right-of-way and extending, where feasible and reasonable, within available portions of adjoining property. Slopes of 4:1 (horizontal : vertical) or flatter are desirable for roadside safety however cut slopes up to 3:1 are considered recoverable. Flatter slopes also contribute to ease of mowing, reduced incidence of slope erosion problems, and improved aesthetics along the property frontage. Cut slopes steeper than 3:1 are considered critical.
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5.7.2.B. Slope rounding shall be provided where practical. This softens the appearance of slopes and grade breaks along properties abutting the highway corridor.
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5.7.2.C. In no case shall any cut slope or fill slope be graded steeper than 2:1 unless a site-specific geotechnical study and design have been approved by the MDOT SHA Office of Materials Technology.
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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.
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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.
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5.7.4.A. Roadside Recovery Zone – Refer to the
AASHTO Roadside Design Guide and the
SHA Guidelines for Traffic Barrier Placement and End Treatment Design for determination of appropriate clear zone distances. The following chart illustrates generally-acceptable clear zone widths. Note the widths provided may not be suitable for all applications.
Design Speed
(mph) | Clear Zone Distance *
(ft) |
|---|
| Less than or equal to 40 | 16 |
| 45 to 50 | 24 |
| 55 or above | 30 |
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5.7.4.B. Protection for Steep Slopes and Fixed Objects – Any fill slope steeper than 3:1 and more than 7’ high shall be considered critical. The grading needs to be adjusted, or the slope shall be protected with traffic barrier. In addition, fixed objects that are considered roadside hazards and cannot reasonably be located, or relocated, to points outside of the roadside clear zone shall be protected with traffic barrier. Generally 3’ of area behind proposed traffic barrier w-beam is required to account for dynamic deflection. Additional area needs to be accounted for when installing end treatments depending on the characteristics of the end treatment i.e. gating, non-gating, or semi-gating. Stiffening methods, including decreasing post spacing and nesting rail elements, can be incorporated into the design to reduce the dynamic deflections. Soil backing provides support for the traffic barrier w-beam posts and is required to be a minimum 2’. Otherwise, 8’ posts will be required in lieu of the generally-acceptable 6’ posts. Refer to the AASHTO Roadside Design Guide and the
MDOT SHA Guidelines for Traffic Barrier Placement and End Treatment Design for additional information regarding dynamic deflection, stiffening methodology, and soil backing, along with placement criteria on slopes and other relevant information pertaining to roadside design.
5.8 Paving
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.
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5.8.1 Specifications – All paving within the MDOT SHA right-of-way, without exception, shall be in accordance with the current SHA paving specifications for Superpave Asphalt and/or Portland Cement Concrete.
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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.
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5.8.2.A.Type I – Standard pavement sections furnished by the SHA Office of Materials Technology (OMT) shall be used for routine projects, except in the following situations::
- (1) (1) If the site access is coordinated with an SHA project under construction or pending construction, the same pavement section should generally be used for the site access improvements.
- (2) If unusual site conditions or pavement failures are evident, assistance should be sought from OMT. There may be an underlying condition, such as poor subgrade, drainage, or slope failure that needs to be addressed.
- (3) If unusually large truck volume is anticipated and/or significant rutting exists in the existing roadway, assistance from OMT should be sought. A different PG binder selection may be appropriate for low-speed, high-volume, stop-and-go traffic conditions.
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.
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5.8.2.B. Type II – For intermediate projects, SHA staff will request and obtain a “network level” pavement recommendation from OMT. This recommendation will address available historical pavement data and project information, existing pavement conditions, and site conditions. Typically, the recommended paving section will match the existing mainline section.
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.
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5.8.2.C. Type III – A detailed pavement and geotechnical investigation and recommendation is mandatory for major development projects. The developer/engineer is responsible for conducting the investigation and developing a Geotechnical and Pavement Report for review and approval by OMT. The developer/engineer is responsible for furnishing all required cores, soil borings, engineering computations, etc. that may be required for approval in accordance with SHA guidelines. The Geotechnical and Pavement Report shall contain the following information:
- (1) Geotechnical investigation – soil identification and material properties.
- (2) Subgrade soil strength testing – resilient modulus or cbr.
- (3) Traffic analysis – approved traffic count, truck weight, truck %, directional distribution (obtain from approved Traffic Impact Study and/or MDOT SHA records).
- (4) Pavement design analysis.
- (5) Geotechnical design analysis.
For detailed information, please refer to OMT’s guidelines.
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5.8.3 Existing Shoulders – The existing shoulders along many older state highways were not designed to support highway traffic on a regular basis. Although shoulders may have been overlaid with additional asphalt layers, they are often not suitable for carrying highway traffic. Therefore, existing shoulders within the limits of the improvements shall be removed completely and replaced with new full-depth paving, unless SHA determines
prior to issuance of the Access Permit that the existing shoulders are suitable for supporting highway traffic. Such a determination may be sought by the applicant through one or more of the following methods:
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5.8.3.A. Pavement Cores – If existing shoulders are believed to be traffic bearing, the applicant may elect, at their own expense, to obtain core samples of the existing pavement. The Resident Maintenance Engineer shall be contacted prior to any pavement disturbance to authorize and observe the coring process. Only qualified professional geotechnical firms will be authorized to obtain core samples. To be considered traffic bearing, the cores must show a depth and composition of pavement that is comparable to the existing highway travel lane paving section and/or current standards. It should be understood that a “built-up” pavement section of a given thickness is not necessarily equivalent, in terms of traffic-bearing capabilities, to a new section of the same thickness.
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5.8.3.B. Existing Full Depth Shoulders – As-built plans showing full-depth shoulder construction are acceptable evidence in lieu of pavement cores. These plans may be available from MDOT SHA records.
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5.8.3.C. Forthcoming Project – Confirmation that full depth paving will be addressed on an MDOT SHA project that is funded for construction, with appropriate developer cost contribution to that project.
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.
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5.8.4 Sawcut and Pavement Removal – A full-depth vertical saw-cut is required at the edge of all pavement removal and replacement and/or base-widening to form a proper joint between new pavement and existing pavement. The vertical face shall be tack-coated prior to placing the new pavement. This requirement should be noted on the plans.
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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.
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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.
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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.
- (1) With this technique, existing flow lines, cross-slopes, and street grades are maintained. This approach is typically used where existing flow lines need to be maintained for positive drainage or where further overlay against existing curbs would be undesirable.
- (2) A wedge/level course can be specified if there is a need for grade corrections/adjustments. Refer to
Paving Specifications for the appropriate paving specification and maximum lift thickness.
- (3) No transitions are required for the tie-ins at the limits of the resurfacing.
- (4) Refer to the detail in
Standard Road Widening and Paving Details.
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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.
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5.8.8.A. Overlay Thickness and Specification:
- (1) A 1 ½" overlay (9.5mm mix) or 2" overlay (12.5mm mix) on existing pavement in sound condition is acceptable. Localized grinding of existing thermoplastic pavement markings is required prior to the overlay.
- (2) Refer to
Paving Specifications for the appropriate paving specification and maximum lift thickness.
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5.8.8.B. Longitudinal Tie-Ins for Overlays – A transverse portion of the existing pavement shall be removed so that the surface course ties in smoothly with existing surfaces to remain and the design thickness of the surface course is maintained.
- (1) The transition should be at a rate of 1":50’ for secondary roadways and 1":100’ for primary highways. On low-speed roadways (< 40mph) and local street tie-ins, 25’ is acceptable.
- (2) The limits and transitions for the overlay shall be specified on the plans.
- (3) Refer to the detail in
Standard Road Widening and Paving Details.
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5.8.8.C. Lateral Tie-Ins for Overlays
- (1) On undivided roadways, the following are acceptable practices:
- (a) Overlay extending across the entire roadway (both travel directions) with uniform thickness; or
- (b) Overlay extending across a portion of the roadway (e.g. up to the centerline only) which has been milled/ground equal to the thickness of the overlay (termed “at-grade resurfacing”).
- (2) Overlaying only half of the roadway without milling/grinding and "heeling in" or “notching” the overlay lift is not acceptable. This has the potential to cause a number of problems, including unsafe drop-off; reduced cross-slope on the overlaid lane, shifted roadway crown, and altered roadway drainage/sheet flow patterns.
- (3) Refer to the paving details in
Standard Road Widening and Paving Details for approved practices.
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5.8.8.D. Pavement Preparation – Refer to Section 504 of the latest specifications.
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.
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5.8.9.A. Patching Specification and Thickness – Refer to
Paving Specifications for the appropriate material to specify for full-depth or partial-depth patching of the roadway.
5.9 Curb-and-Gutter, Medians, and Traffic Control Islands
Curb-and-gutter, medians, and traffic control islands shall conform to the following guidelines.
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5.9.1 Type of Channelization – The type of channelization will be selected based on safety considerations and the purpose of its application. Considerations include the function and anticipated travel speeds on the highway, roadside grading conditions, presence of fixed objects within the effective roadside recovery zone, adjacent property use, and the degree of access restriction required.
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5.9.1.A. Type 'A' – Type ‘A’ channelization shall be used for barrier curb applications along closed-section highways in urban areas. Posted speeds should not exceed 40 mph. Localized use of Type ‘A’ channelization may be acceptable along auxiliary lanes (e.g. right turn lane, acceleration lane, etc.) where necessary to control vehicular movements along property frontage where the posted speed is no higher than 45 mph.
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5.9.1.B. Type 'B' – Type ‘B’ channelization shall be used for traffic control islands and medians only and when normal operating speeds are between 40 and 50 mph.
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5.9.1.C. Type 'C' – Type ‘C’ channelization shall be used along highways that have graded roadside recovery areas included in their existing design and along any highway with an operating speed higher than 50 mph. It is also used for isolated entrances along predominantly open-section, rural routes.
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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.
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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.
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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.
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5.9.4.A. Minimum Width
- (1) Minimum width for medians between opposing traffic streams shall be 4’. This shall be increased to 6’ where pedestrian refuge is incorporated into the median design, such as at a signalized intersection.
- (2) Minimum width for medians for protected left-turn lanes is generally 4’, to accommodate the required signing.
- (3) Medians designed to accommodate future left-turn lanes shall be wide enough to include a 6’ median and the appropriate left-turn lane width from
5.6.4 Bypass Lanes.
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5.9.4.B. Construction Standards
- (1) Medians less than 6’ wide shall be constructed of Standard Monolithic Concrete Median Type ‘A’ (conforming to Standard No. MD-645.01 Type A-1 or A-2 as applicable)/Type B (conforming to Standard No. MD-645.02 Type B-1 or B-2 as applicable)/Type C (conforming to Standard No. MD-645.03 Type C-1 or C-2 as applicable). Medians 6’ wide or less shall conform to the details for Standard Monolithic Median.
- (2) Medians greater than 6’ wide shall utilize the appropriate type of Standard Curb-and-Gutter based on the design requirements of
5.9.1 Type of Channelization. The top surface between curbs shall be grassed, landscaped, or paved as acceptable to MDOT SHA.
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.
5.11 Structures
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.
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5.11.1 Bridges – The design plans for any bridge, or any other structure proposed to span across a state highway or carry the state highway traffic 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. During construction, working drawings shall be submitted as outlined in the
Standard Specifications for Construction and Materials.
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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.
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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.
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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
structurechecklists@mdot.maryland.gov for the latest version of the checklists prior to submitting structure plans.
5.12 Sidewalks
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5.12.1 Pedestrian Accommodations – The MDOT SHA has developed design guidelines for the preferred accommodations to benefit pedestrian traffic 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 pedestrian accommodations is especially important where the existing or proposed land use supports walking. 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.
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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.
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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.
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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 Construction 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.
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5.14.1 Signs – Signing appropriate for the proposed access and/or road improvements is required in accordance with standards and practices accepted by MDOT SHA. The MDOT SHA Office of Traffic and Safety (OOTS) maintains an inventory of standards for signs and supporting structures. Existing signs affected by the access and/or improvements shall be removed and replaced, reset, or relocated as determined during the project review process.
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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.
5.16 Lighting
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.
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5.17.1 Guidelines – Traffic controls shall conform to the latest version of the
MDOT SHA Standard Temporary Traffic Control Typical Applications and the Maryland Manual on Uniform Traffic Control Devices (MDMUTCD).
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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.
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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.
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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.
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5.17.5 Drop-Off Requirements – Traffic control required as a result of pavement elevation differences shall be in accordance with the
MDOT SHA Pavement Drop-Off Guidelines. During off-work hours, drop-off must be addressed in accordance with these Guidelines or be protected by Temporary Concrete Traffic Barrier. When a need for Temporary Concrete Traffic Barrier is anticipated, formal Traffic Control Plans shall be submitted for approval. The applicant should coordinate with the Assistant District Engineer - Construction to ascertain specific requirements based on the latest drop-off guidelines, which are illustrated in the MDOT SHA Standard Work Zone Traffic Control Typical Applications.
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:
| Application | Minimum Clearance |
|---|
| Closed-section, posted speed of 40 mph or less, sidewalk at curb |
 2’ behind face of barrier curb
Behind sidewalk if necessary to comply with ADA |
| Closed-section, posted speed > 40 mph |
Outside of the roadside clear zone, as defined in 5.7.4 Roadside Grading, where feasible and reasonable as determined by SHA.
Otherwise, 6’ behind face of curb or min. 5’ behind guardrail posts. |
| Open-section, any speed |
Outside of the roadside clear zone, as defined in 5.7.4 Roadside Grading, where feasible and reasonable as determined by SHA.
Otherwise, beyond ditch line or 6’ min. from edge of shoulder. Min. 5’ behind guardrail posts. |
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.