15. TECHNICAL DESIGN STANDARDS
15.1 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 applicant and/or their professional representative is responsible for compliance with all applicable standards of design practice.
In presenting certain requirements, reference is made to the definitions of "routine", "intermediate", and "major" projects, which are found in Chapter 7.
15.2 Standards and Specifications
15.2.1 Design Standards.
All designs shall conform to the policies, guidelines, standard practices, and directives issued by SHA and EAPD and the following nationally recognized publications, as applicable:
- A Policy on Geometric Design of Highways and Streets, American Association of State Highway and Transportation Officials, 2001.
- Manual on Uniform Traffic Control Devices, American Association of State Highway and Transportation Officials, 2000.
- Roadside Design Guide, American Association of State Highway and Transportation Officials, 1996.
- Other publications, guidelines, standards, and directives recognized and applied by various SHA design offices as may be applicable to the project design.
15.2.2 Construction and Materials Specifications.
All construction on the State highway right-of-way shall conform to the latest version of SHA’s Standard Specifications for Construction and Materials, including all applicable Interim Specifications Addenda and Special Provision Inserts. In addition, work shall conform to any approved project-specific provisions.
15.2.3 Standard Details.
All construction shall conform to the latest version of SHA’s Book of Standards for Highway and Incidental Structures, except where the use of nonstandard or modified designs is expressly noted and detailed on the approved plans. This requirement shall apply regardless of whether the details are included or referenced on the approved plans.
15.3 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.
15.3.1 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 11 and 12, respectively. The layout of street connections for collector or arterial routes shall conform to 15.3.3, below.
15.3.2 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 13. 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.
15.3.3 Highway Infrastructure Improvements.
The layout of highway infrastructure improvements shall conform to the requirements outlined in Chapter 14, together with the latest version of the AASHTO policies referenced in 15.1 above, all relevant 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 option. The geometric layout of site access improvements proposed within the limits of a highway infrastructure improvement shall conform to the requirements of Chapter 13.
15.4 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 SHA practices. Developing safe and appropriate alignments for new highways is a complex engineering endeavor which requires proper application of many technical criteria. Excerpts from SHA policy on the design of new alignments are contained in Appendix G.
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.
15.4.1 Design Speed.
For geometric design purposes, an operating speed of 10 mph above the existing or anticipated posted speed limit shall be assumed. A lower design speed may be considered but only if supported by an approved speed study that indicates a lower 85th percentile operating speed.
15.4.2 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. Pertinent SHA design practices for horizontal curves are given in the sections below and in Appendix G.
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 15.4.2. 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.
B. Superelevation Transitions. Superelevated sections shall be gradually introduced, with a uniformly varying cross slope, over an appropriate distance referred to as the transition length. The appropriate transition length shall be determined using the following chart.
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.
15.4.3 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. Pertinent SHA standards for vertical curve design in Appendix G shall apply.
15.4.4 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.
15.5 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.
A. Widening Along Normal Sections. On Normal Sections, the existing roadway is crowned at the centerline. Grades for the widening shall be established using the existing or proposed pavement elevations at the edge of the widening and an appropriate cross slope for the new pavement. The cross slope of the new pavement shall be - 2% (- ¼ in/ ft) for widening of existing 2-lane undivided highways, unless otherwise directed by EAPD. The cross slope of the new pavement should be increased to –4% (- ½ in/ ft) for widening of existing multilane undivided or divided highways where more than one existing travel lane is sloped towards the widening. A typical section shall be provided on the plans and is generally sufficient to illustrate the proposed road grading.
B. Widening Along Superelevated Sections. In a fully superelevated section, the entire roadway is banked to slope in one direction. In a superelevation transition section, all or a portion of the roadway is progressively rotated from the normal cross slope to the superelevated cross slope. For minor widening that will not affect the location of the centerline or travel lanes, the widening should generally be graded to the same cross slope as that of the adjacent travel lane(s), matching the existing superelevation and transition rates. Topographic coverage must be sufficient to accurately define the existing roadway cross slopes across each lane of the existing highway (“spot” elevations taken at the centerline and each lane line). Cross sections at 50' maximum intervals and/or superelevation tables shall be provided on the plans to define road grading in superelevated and transition sections.
C. Shifted Centerline or Travel Lanes. When grade adjustments within the existing travel lanes are proposed, for example to shift the location of the road crown, cross sections shall be provided at 50' intervals. The cross sections shall be annotated with offsets, existing/proposed elevations, and cross slopes.
D. Rollover. Rollover is defined as the algebraic difference in cross slope between two adjacent paved areas which are separated by a crown or grade break. AASHTO policy establishes the maximum acceptable rollover between two adjacent travel lanes and between a travel lane and a shoulder. The following are taken from 2001 AASHTO policy and are printed here for convenience.
*Design speed of 35 mph or more is assumed for EAPD applications.
For purposes of applying these standards, auxiliary lanes, such as acceleration lanes, deceleration lanes, and bypass lanes are considered travel lanes, not 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.
E. Intermediate and Major Projects. Cross sections of the improvements shall be provided at 50' intervals, in accordance with SHA practices, at a scale of 1"=10'.
15.6 Lane and Shoulder Widths
Appropriate widths must be provided for all lanes and shoulders created or modified in connection with the proposed access. Requirements are as follows:
15.6.1 Closed Section/Curb Lanes.
Standard widths for closed section turning lanes, auxiliary lanes, and other travel lanes adjacent to curb and gutter are given in Table 15.6.1. These guidelines are based on SHA policy regarding bicycle accommodations on State highways in effect at the time of this publication and are subject to change.
- Widths indicated are for shoulders along the outside edge of the highway.
- For the above applications, the 4' shoulder is not normally delineated by pavement markings. The designated bike lane/shoulder generally would be delineated by a 5" solid white edge line and, where recommended by the Office of Traffic and Safety, the appropriate bike lane/route pavement markings and signing.
15.6.2 Open Section/Shoulder Widths.
New or modified shoulders shall conform to AASHTO and SHA standards as appropriate for the specific highway function and location. On any highway, EAPD may require the existing shoulder widths to be maintained. In general:
A. Routine Site Access Improvements.
- Applies to localized, access-specific improvements identified in Chapter 13.
- Shoulders of at least 4' width shall be provided along all open section improvements. A 5" solid white edge line separates the shoulder from the travel lane.
- For open section improvements along Primary highways, new shoulders shall be at least 4' wide or as wide as the existing shoulders, whichever is greater.
- For open section improvements along Secondary highways, new shoulders must be at least 4' wide. Additional width may be required for high speed and/or high volume arterial highways, at the discretion of the SHA, in accordance with AASHTO guidelines.
- Existing shoulders that are affected by the improvements, but not incorporated into the improvements, shall be maintained in accordance with the requirements of 15.6.6. For example, a minimum 4’ shoulder must be maintained along an improvement that utilizes a portion of an existing 8’ wide traffic-bearing shoulder.
B. Highway Infrastructure Improvements.
- Applies to improvements identified in Chapter 14.
- New and replacement shoulders shall comply with AASHTO standards.
- 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 15.6.6. 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.
15.6.3 Through Lane Widths.
Standard widths for through lanes on State highways shall comply with AASHTO standards and the following SHA guidelines. Reduction of through lane widths to below these standards in order to accommodate proposed traffic patterns and lane configurations is not acceptable.
15.6.4 Width of Left Turn Lanes and Center Turn Lanes.
- Desirable width for left turn lanes is 12’, required where feasible and reasonable. Minimum under any circumstances is 10'.
- 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.
- The median gutter pan, if applicable, is included in these widths.
15.6.5 Bypass Lanes.
- Standard bypass lanes are 12' wide with a 4' minimum shoulder. The lane width may be reduced to 11’ in low-speed urban areas; however, the shoulder width may not be reduced.
- Where there is no existing shoulder along the State highway, the 4' shoulder may be waived as long as a suitable roadside condition is provided in accordance with 15.6.4.
- Bypass lanes shall be open section except along urban closed section highways or where a curb is necessary for proper drainage.
15.6.6 Bicycle Accommodations.
SHA has developed design guidelines for the preferred accommodations to benefit bicycling and walking along State highways. It is SHA’s goal to provide the preferred accommodations as part of all roadway projects where feasible and reasonable. Providing bicycle and pedestrian accommodations is especially important where the existing or proposed land use supports cycling and walking. This includes trip generators and destinations such as employment, education, residential, commercial, recreation, and transit centers. While it is SHA’s intent to provide the preferred accommodations on all projects, it is understood that projects will be reviewed on a case-by-case basis.
- Proposed Improvements. All state highway improvements shall be bicycle compatible and provide the preferred bicycle accommodations in accordance with SHA guidelines, including but not limited to 15.6.1 and 15.6.2, where feasible and reasonable as determined by SHA. Further guidance on various types of bicycle accommodations may be obtained in the Guidelines for Accommodating Bicycles and Pedestrians on State Highways.
- Existing Conditions. Where existing conditions along the State route are capable of supporting bicycle traffic, as determined by 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 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 Guidelines for Accommodating Bicycles and Pedestrians on State Highways.
15.7 Roadway Excavation and Slope Grading
15.7.1 Roadway Excavation.
- Excavation for the road template shall accommodate the specified Hot Mix Asphalt or Portland Cement Concrete pavement section, including the supporting base course consisting of graded aggregate or borrow material.
- The graded aggregate or borrow material shall extend underneath of curb and gutter sections and at least 1 ft beyond.
- 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 SHA in order to attain specified compaction of the subgrade prior to paving. Refer to the Paving requirements in 15.7.
15.7.2 Cut Slopes.
- Cut 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 or flatter are desirable for roadside safety because they are considered traversable and recoverable from the standpoint of roadside safety design. Flatter slops also contribute to ease of mowing, reduced incidence of slope erosion problems, and improved aesthetics along the property frontage.
- Slope rates shall conform to the following chart, which reflects the economy of steeper slopes for deeper cuts. Roadside grading considerations are to be addressed separately.
- Slope rounding shall be provided where practical. This softens the appearance of cut slopes and grade breaks along properties abutting the highway corridor.
- In no case shall any cut slope or fill slope be graded steeper than 2:1 (horizontal : vertical) unless a site-specific geotechnical study and design have been approved by SHA’s Geotechnical Explorations Division.
15.7.3 Fill Slopes.
- Fill slopes shall be graded as flat as possible within the State right-of-way and extending, where feasible and reasonable, within available portions of adjoining property. Slopes of 4:1 or flatter are desirable for roadside safety, ease of mowing, and minimization of slope erosion problems. In addition, flatter fill slopes provide improved aesthetics by softening the appearance of the road fill along the property frontage.
- Slope rates should generally conform to the following table, which reflects economy of steeper slopes for higher fills.
- In no case shall any cut slope or fill slope be graded steeper than 2:1 (horizontal : vertical) unless a site-specific geotechnical study and design have been approved by SHA’s Geotechnical Explorations Division.
15.7.4 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), to promote a safe vehicular recovery area wherever feasible and reasonable, as determined by the SHA. Roadside designs that are suitable for the safe recovery of errant vehicles shall be provided for the following applications, among others:
- All open sections.
- Closed sections with mountable curb (SHA Type ‘B’ or ‘C’).
- Closed sections on urban highways with barrier curb (SHA Type ‘A’) and posted speeds of 50 mph or above.
- General guidelines based on the AASHTO Roadside Design Guide are discussed below.
A. Roadside Recovery Zone. A 30’ clear roadside recovery zone is generally appropriate under a wide range of highway operating speeds. This distance is measured from the edge of the active traveled way outward. A reduced clear zone requirement may be justified for highways with lower speeds or lower traffic volumes, using the Roadside Design Guide. The following chart, based on application of the RDG to routine design situations, is provided for the convenience of applicants but may not be suitable for all applications.
*NOTE: Distance is measured outward from the edge of the travel lane and includes the shoulder. Distances shown are for roadside slopes of 4:1 or flatter, along a tangent highway alignment, with ADT of 6000 or higher. 3:1 slopes are not to be considered part of the available clear zone distance.
B. Roadside Slopes. Slopes of 4:1 or flatter are considered recoverable and shall be used along the improvements whenever possible. Slopes of 3:1 are considered traversable without vehicle turnover; however, they are not credited towards fulfilling the clear zone distance requirement. Slopes of 2:1 are neither recoverable nor traversable and shall not be located within the roadside recovery zone.
C. Protection for Steep Slopes and Fixed Objects. Any fill slope steeper than 3:1 and more than 5’ high shall be considered non-traversable and protected with Standard Traffic Barrier W Beam and appropriate Standard end sections. Fixed objects that cannot reasonably be located, or relocated, to points outside of the roadside recovery zone shall be protected with Standard Traffic Barrier W Beam and appropriate Standard end sections. There must be at least 5’ clear space between the traffic barrier and the fixed object, to allow for guardrail deflection.
D. Ditch Grading. Ditch cross sections shall be in accordance with current adopted SHA design criteria. The ditch sections shall be designed to provide appropriate roadside design and drainage characteristics, in accordance with standard engineering practices as acceptable to the SHA. End sections shall be used on all unprotected culverts within the clear zone distance. Refer to the drainage requirements in Section 13.9.
E. Grading for Traffic Barrier "Guardrail". Grading shall conform to the requirements identified in the standard details for Traffic Barrier W Beam and Traffic Barrier W Beam End Treatments. This may require local deviation from the typical sections of the improvement to accommodate a specific end treatment, or the grading may dictate the selection of an appropriate end treatment.
F. Sub-Standard Roadside Conditions. Where open section roadside grading per these standards is not feasible due to demonstrated grading, utility, or property availability constraints, the proposed roadside grading shall be designed to approximate the existing conditions along the highway adjacent to the improvements.
15.7.5 Limits of Disturbance.
The limits of disturbance shall be shown on the plans and adjacent property impacts need to be clearly indicated. The disturbance along the frontage of adjacent properties should be limited to the minimum necessary to construct the specified scope of improvements in accordance with the guidelines. In environmentally sensitive or protected areas, the limits of disturbance may need to be precisely identified with respect to individual structures, natural resources, properties, and features as acceptable to the approving authorities for the related impacts or avoidance measures.
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. EAPD staff will furnish the latest approved pavement sections and mix designations upon request. As noted herewith, some projects require design approval from SHA’s Pavement Division.
All paving within the SHA right-of-way, without exception, shall be in accordance with the current SHA paving specifications for Hot Mix Asphalt Superpave and/or Portland Cement Concrete.
15.8.2 Full Depth Pavement Sections.
Full-depth paving shall conform to the sections and specifications identified in the permit by SHA. 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. A. Routine Projects. Standard pavement sections furnished by the Pavement Division shall be used for routine projects, except in the following situations:
- 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.
- If unusual site conditions or pavement failures are evident, assistance should be sought from Pavement Division. There may be an underlying condition, such as poor subgrade, drainage, or slope failure that needs to be addressed.
- If unusually large truck volume is anticipated and/or significant rutting exists in the existing roadway, assistance from the Pavement Division should be sought. A different PG binder selection may be appropriate for low-speed, high volume, stop-and-go traffic conditions.
- Projects in Garrett County require a different PG binder selection. Assistance from the Pavement Division is required.
The standard pavement sections for routine projects are given in Appendix D. These are broken down into Standard Duty and Heavy Duty for use on different types of highways with different traffic conditions. These sections are subject to periodic update by the Pavement Division.
B. Intermediate Projects. For Intermediate projects, EAPD staff will request and obtain a “network level” pavement recommendation from the Pavement Division. 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 at their own cost. If the results of their investigation indicate that the Pavement Division’s recommendations are over-conservative for the site conditions, the report of their investigation should be submitted to the Pavement Division for further review and re-evaluation of the pavement recommendations.
C. Major Projects. 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 the Pavement Division and Geotechnical Explorations Division. 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:
- geotechnical investigation – soil identification and material properties.
- subgrade soil strength testing – resilient modulus or CBR.
- traffic analysis – approved traffic count, truck weight, truck %, directional distribution (obtain from approved TIS and/ or SHA records).
- pavement design analysis – design inputs provided.
- geotechnical design analysis.
For detailed information, please refer to the OMT's guidelines.
15.8.3 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:
- 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.
- Existing Full Depth Shoulders. In recent years, SHA projects included full depth shoulder paving instead of stabilized aggregate shoulders. As-built plans showing the full depth shoulder construction are acceptable evidence in lieu of pavement cores. These plans may be available from SHA records.
- Forthcoming Project. Confirmation that full depth paving will be addressed on an 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 grinded, wedge/leveled, and overlaid to the required cross slope. Refer to the details in Appendix C. 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.
15.8.4 Sawcut and Pavement Removal.
A full-depth vertical sawcut 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.
15.8.5 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, a pavement patch consisting of concrete base and HMA surface shall be provided as detailed in Appendix C.
15.8.6 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 Appendix C.
15.8.7 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.
- With this technique, existing flow lines, cross-slopes, and street grades are maintained. This approach is typically used where existing flow lines need to maintained for positive drainage or further overlay against existing curbs would be undesirable.
- A wedge/level course can be specified if there is a need for grade corrections/adjustments. Refer to Appendix D for the appropriate paving specification and maximum lift thickness.
- No transitions are required for the tie-ins at the limits of the resurfacing.
- Refer to the detail in Appendix C.
15.8.8 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 SHA.
A. Overlay Thickness and Specification:
- A 1-1/2" overlay (9.5mm mix) or 2" overlay (12.5mm mix) on existing pavement in sound condition is acceptable. Localized grinding off of the existing thermoplastic pavement markings is required prior to the overlay.
- Refer to Appendix D for the appropriate paving specification and maximum lift thickness.
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.
- 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.Appendix C.The limits and transitions for the overlay shall be specified on the plans.Appendix C.Refer to the detail in Appendix C.
C. Lateral Tie-Ins for Overlays.
- On undivided roadways, the following are acceptable practices:
- Overlay extending across the entire roadway (both travel directions) with uniform thickness; or
- Overlay extending across a portion of the roadway (e.g. up to the centerline only) which has been milled/grinded equal to the thickness of the overlay (termed “at-grade resurfacing”).
- 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.
- Refer to the paving details in Appendix C for approved practices.
D. Pavement Preparation. Existing pavement shall be cleaned and tack-coated prior to placement of the overlay.
15.8.9 Pavement Patching.
The following guidelines apply to patching required to address substantially increased traffic volumes or to repair pavement damaged during construction.
A. HMA Patching Specification and Thickness. Refer to Appendix D for the appropriate material to specify for full-depth or partials-depth patching when the roadway is known to have a flexible pavement structure (HMA only). If the existing HMA pavement thickness is extremely thick (> 10 inches), the patching specification must be obtained from OMT Pavement Division.
B. Rigid Pavement Patching. If the roadway has a rigid pavement structure (Portland Cement Concrete) or a composite pavement structure (HMA and PCC), the patching specification must be obtained from OMT Pavement Division.
15.9 Curb and Gutter, Medians, and Traffic Control Islands
Curb and gutter, medians, and traffic control islands shall conform to the following guidelines.
15.9.1 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.
- 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 the posted speed is no higher than 45 mph. However, the area behind the curb should comply with roadside clear zone requirements or be protected by Traffic Barrier W Beam “guardrail”.
- Type 'B'. Type ‘B’ channelization shall be used for traffic control islands and medians only, when normal operating speeds are between 40 and 50 mph.
- 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.
15.9.2 Curb and Gutter.
Curb and gutter all consist of Standard Concrete Combination Curb and Gutter Type ‘A’ or Type ‘C’ (conforming to Standard No. MD-620.02 with a 1’-0” wide gutter pan). All curbs shall have a minimum of 3 1/2' compacted earth backing for support, sloping up 1/2" per foot from top of curb for a minimum of 3 1/2', thence on a slope not in excess of 2:1. 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.
Temporary bituminous curb may be used in lieu of concrete curb and gutter if highway improvements along the property frontage are funded in the Consolidated Transportation Program for construction within 6 years, whether or not advertised.
Depressed curb entrances shall be constructed in accordance with the SHA standard details. The apron shall be poured separately from the curb and gutter.
15.9.3 Traffic Control Islands.
Geometric design of islands shall conform to AASHTO policy, 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 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 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, a grass surface may be acceptable instead of the concrete sidewalk.
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.
- Minimum Width.
- Minimum width for medians between opposing traffic streams shall be 4 feet. This shall be increased to 6 feet where pedestrian refuge is incorporated into the median design, such as at a signalized intersection.
- Minimum width for medians for protected left turn lanes is generally 4 feet, to accommodate the required signing.
- 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 15.6.4.
- Construction Standards.
- 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.
- Medians greater than 6’ wide shall utilize the appropriate type of Standard Curb and Gutter based on the design requirements of Section 15.9.1. The top surface between curbs shall be grassed, landscaped, or paved as acceptable to SHA.
15.10 Drainage/Hydraulic/Hydrologic Requirements
Approval from SHA’s Highway Hydraulics Division is required for all projects that will affect State highway drainage conditions or facilities. EAPD determines whether a hydraulic/hydrologic review is required for each project. Refer to the “Guidelines for Development Adjacent to State Highways” for information on the requirements for review and approval. The latest version of this document is included in Appendix H.
15.10.1 General Requirements for Site Storm Drainage Facilities Not Tied Into Existing Highway Drainage Facilities.
Stormwater management plans should be reviewed and approved by the appropriate approving authority. The discharge rate after development shall not exceed the rate before development for the 2-, 10-, and in some instances, the 100-year storm events. The State Highway Administration will institute legal proceedings upon being damaged by increased storm water runoff to recover any costs and to avoid recurrence.
15.10.2 General Requirements for Site Storm Drainage Facilities Connect to Existing State Facilities.
The proposed storm water management plans must be reviewed by the SHA following their approval by the appropriate approving authority. The State will review the proposed facilities based on the design year storm of the existing State facilities. The design year storm is based on the Federal functional classification of the State highway.
15.10.3 Stormwater Management/Approving Authority.
Changes in stormwater runoff generated by the development, including the permitted improvements on the State highways, shall be managed as required by the approving authority. The permittee or owner is responsible for carrying stormwater runoff to an outfall in a manner acceptable to the SHA. Acceptable outfalls, and their associated contributing drainage facilities, shall meet the design criteria set forth by SHA.
The approving authority for stormwater management and sediment control for privately funded improvements on the State's right of way is the local jurisdiction and/or Soil Conservation District but not the SHA. SHA's review is concurrent with, but not a substitute, for the appropriate approval. If the local jurisdiction or SCD does not review the improvements within State right-of-way, the applicant should obtain approval from the Maryland Department of the Environment's Water Management Administration to ensure compliance with the applicable regulations. New or modified stormwater management facilities proposed within State right-of-way, if acceptable to SHA, are subject to concurrent review and approval by the Maryland Department of the Environment
15.10.4 Erosion and Sediment Control/Approving Authority.
Sediment and erosion control devices shall be established for the permitted improvements as required by the approving authority. The County, local jurisdiction, or Soil Conservation District is the approving authority for projects that are not State or federally funded.
15.10.5 Minimum Information Required for Review.
Information which is required to properly determine the effect of proposed drainage facilities on existing highway drainage facilities is as follows:
15.10.6 Staged Construction and Maintenance of Drainage.
All existing drainage systems (including, but not limited to ditches structures, inlets, pipes, outfalls, etc.) shall continue to function in an effective manner while work is in progress, as well as upon completion of work. Should any disturbance be made to existing drainage systems, you must restore them to their original condition and function using appropriate methods (including, but not limited to, structural replacement, cleaning out, resodding, stabilization practices and paving).
15.10.7 Field Changes.
In the event that the permitted storm drainage or stormwater management facilities can not be constructed according to the approved plans due to utility conflicts, adverse site conditions or other factors discovered during construction, it is the responsibility of the Permittee to accomplish a functionally equivalent design and submit revised plans to SHA for approval.
15.10.8 Drainage Standard Structures.
All new or replacement drainage structures shall conform to the latest version of SHA’s Book of Standards for Highway and Incidental Structures, except where the use of modified or non-standard structures is expressly noted on the approved plans. All new or replacement drainage pipes shall conform to approved materials listed in the latest version of Section 905 of the SHA Standard Specifications.
15.10.9 Utility Clearances.
Clearance with any existing utility shall be in accordance with the criteria established by the utility owner. Underground utilities shall be located and clearances determined prior to submission of final design plans, using appropriate engineering methods including test pitting. Test pitting during the design phase, prior to issuance of the permit, must be coordinated with and permitted by the District Utility Engineer. Should utility conflicts arise during construction, an alternative design will be required that is functionally equivalent to the permitted design and will require approval from the Highway Hydraulics Division. Unforeseen or improperly evaluated conflicts with underground utilities can have a profound effect on the schedule and cost of construction. Redesign of proposed storm drainage systems may require considerable engineering efforts and relocation of the utility may be the only acceptable alternative. Applicants are advised to utilize appropriate resources to positively identify the precise horizontal and vertical location of all underground utilities at points of potential conflict with proposed storm drainage systems. This practice has been used successfully on State highway projects since the early 1990’s.
15.10.10 Stormwater Management Facilities.
Private stormwater management facilities, including embankments, permanent or storm-event storage, and outlet works structures, are not allowed in State right-of-way. Construction of on-site facilities as necessary to comply with the requirements of the local approving authority and/or SHA is the sole responsibility of the owner/developer. Regional or “joint use” facilities may be allowed within State right-of-way on a case by case basis, in accordance with pertinent policy. For further information on these topics, refer to the latest guidelines of the Highway Hydraulics Division.
Any structures, other than standard storm drainage, sign support, traffic signal equipment, and lighting structures, shall be reviewed and approved by SHA’s Bridge Design Division. Preliminary coordination is important to ensure designs are consistent with SHA requirements and allow time for the development of maintenance agreements.
The review and approval of structures within or impacting 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 Bridge Design Division, the TS&L and Foundation Review may be combined.
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 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. Additional information regarding the minimum information that must be shown on the plans is included in Appendix I. Working drawings during construction shall be submitted as outlined in the Standard Specifications for Construction and Materials.
15.11.2 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 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. Additional information regarding the minimum information that must be shown on the plans is included in Appendix I.
NOTE: Retaining walls that are for site grading purposes shall not be located on the State right-of-way. Such walls shall be located entirely on private property, including all tiebacks, soil anchorages, etc. Retaining walls that are 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 District Office.
15.11.3 Small Structures (Culverts).
The design plans for culverts with a span of 60" or more shall be reviewed and approved by the Office of Bridge Development's Bridge Design Division. Submission of a hydrologic/hydraulic study may also be required for review and approval by the 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. Additional information regarding the minimum information that must be shown on the plans is included in Appendix I.
15.11.4 Special or Non-Standard Drainage Structures.
Special or non-standard drainage structures shall be reviewed and approved by the Bridge Design Division, when this requirement is identified by the Highway Hydraulics Division.
15.12.1 Pedestrian Accommodations.
The SHA has developed design guidelines for the preferred accommodations to benefit bicycling and walking along State highways. It is SHA’s goal to provide the preferred accommodations as part of all roadway projects where feasible and reasonable. Providing bicycle and pedestrian accommodations is especially important where the existing or proposed land use supports cycling and walking. This includes trip generators and destinations such as employment, education, residential, commercial, recreation, and transit centers. While it is SHA’s intent to provide the preferred accommodations on all projects, it is understood that projects will be reviewed on a case-by-case basis.
15.12.2 Preferred Sidewalk Facilities.
Continuous 5 foot 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. Minimum 4 foot shoulders are preferred on all rural roadways or open section roadways to support walking. 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.
15.12.3 Design Requirements.
All sidewalks, ramps, and pedestrian facilities shall be designed to conform to the requirements of the Americans with Disabilities Act and pertinent guidelines established by the U.S. Architectural and Transportation Barriers Compliance Board (American Disabilities Act Accessibility Guidelines) and AASHTO. Requirements include, but are not limited to, the use of appropriate sidewalk ramps, widths, landings, railings, slopes, and surfaces. The applicant should refer to SHA's interim ADA Guidelines in Appendix G for further information on currently accepted current practice.
15.12.4 Construction Specifications.
Unless the local jurisdiction requires use of a different specification, sidewalks constructed in the State's right-of-way shall be constructed of 5" of SHA Concrete Mix No. 2 in accordance with the Standard Specifications 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 1/4" per foot for the total width of the sidewalk.
15.13 Traffic Barrier
The installation or modification of traffic barrier w beam "guardrail" may be required whenever warranted for safety as determined by SHA. Existing traffic barrier may need to be removed and reset or relocated to accommodate the proposed improvements or different traffic patterns.
15.13.1 New Installations.
Standard Traffic Barrier W Beam and appropriate Standard End Treatments shall be installed, where warranted, in accordance with the latest SHA standard details and specifications. The appropriate type of end treatment must be identified on the plans, in accordance with the selection guide included in Appendix G.
15.13.2 Adjustment of Existing Installations.
Existing Traffic Barrier W Beam affected by the improvements shall be removed and reset in accordance with the SHA Standard Specifications and end treatments shall be upgraded to meet current standards. For purposes of definition, “affected” means directly impacted by the improvements or subjected to more frequent traffic at close proximity. When an existing shoulder is converted to a turning lane or bypass lane, the adjacent traffic barrier w beam shall be adjusted and updated.
15.14 Landscaping and Streetscape
Streetscape design shall be in accordance with approved Master Plan and SHA standards. Non-conforming, individual, or municipal projects will require review and approval of the design by the Landscape Architecture Division. Improvements that affect conditions within the roadway (as opposed to sidewalk areas only) will require review and approval from a highway design and pavement design standpoint, as applicable.
Formal landscape design plans shall be in accordance with approved Master Plan. Non-conforming, individual, or municipal projects will require review and approval of the design by the Landscape Architecture Division. Informal planting plans will be reviewed and approved by the Landscape Operations Division.
15.15 Signing and Pavement Marking
Signing and pavement markings on State highways shall conform to the Federal Highway Administration's Manual on Uniform Traffic Control Devices, latest edition, and pertinent 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 Traffic Engineering Design Division may be required.
Signing appropriate for the proposed access and/or road improvements is required in accordance with standards and practices accepted by SHA. The Office of Traffic and Safety 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.
15.15.2 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 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.
15.16 Traffic Signals
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 the Traffic Engineering Design Division prior to the issuance of an Access Permit. In order for plans to be processed for review and approval, a Design Request approved by the Director, Office of Traffic and Safety, must be on file. Refer to Chapter 6 for general discussion of traffic studies that are necessary to facilitate a determination of whether a traffic signal may be justified. Following 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.
The design of lighting system installation or modifications shall be in accordance with SHA standards and accepted engineering practice. Standards for roadway lighting, fixtures, and supporting structures are available from the Office of Traffic and Safety. Ornamental street lighting fixtures, illumination levels, and filters shall be designed to avoid glare problems in the adjacent highway. Plans for all new or modified lighting shall be reviewed and approved by the Traffic Engineering Design Division. 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.
15.18 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.
Traffic controls shall conform to the latest version of the Manual on Uniform Traffic Control Devices (MUTCD). The MUTCD 2000 “Millennium Edition” dated December 2000 is current at the time of publication of this guidance document.
15.18.2 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 the Access Permit. The 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.
15.18.3 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 SHA Standard Temporary Traffic Control Typical Applications.
15.18.4 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 between the hours of 9:00 am and 3:00 pm, unless otherwise approved in advance and in writing by the Assistant District Engineer-Traffic.
15.18.5 Drop-Off Requirements.
Traffic control required as a result of pavement elevation differences shall be in accordance with SHA’s 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 SHA Standard Work Zone Traffic Control Typical Applications.
15.19 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 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 SHA:
Additional clearance may be required where necessary to establish or maintain an appropriate roadside clear zone in accordance with 15.7.4.