Download Design Criteria for Roadways: Rural & Urban Freeways, Arterials, and Collector Streets and more Study notes Design in PDF only on Docsity! MONTANA DEPARTMENT OF TRANSPORTATION GEOMETRIC DESIGN STANDARDS September 2016 MDT Geometric Design Standards 1.0 INTRODUCTION The MDT Geometric Design Standards provide design criteria summary tables for the geometric design of MDT rural and urban facilities. Chapter 2: Basic Design Controls of the MDT Road Design Manual (RDM) outlines the basic design controls for the criteria presented in this document. The selection of design values depends on the functional classification of the highway facility. Descriptions for each functional classification category are provided in Chapter 2, Section 2.2 of the RDM. The most recent version of the MDT Functional Classification Map is provided at the following link on the Montana State Official Website. MDT Functional Classification Map Note that, in general, National Highway System (NHS) facilities within the current Federal‐aid system will be designed using the design criteria presented in the freeway tables (Exhibits 1 and 7) and the rural/urban principal arterial tables (Exhibits 2 and 8). Federal code identifies the America Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) and the supplemental A Policy on Design Standards Interstate System as the minimum standard of design for use on the NHS (1, 2). Flexibility in design exists even within full AASHTO standards, and MDT has established standards for some criteria for use on the NHS, within Montana, where AASHTO provides only general guidance or a range of acceptable values. If differences exist between values presented here and in AASHTO, the more conservative values will control for all NHS routes. This is particularly important when routes are added to or removed from the NHS, when revisions to AASHTO standards are made, and when design speeds above the minimum shown are selected. Local agencies may have developed their own geometric design criteria for local facilities. If a facility is not on the State highway system, it may be acceptable to use the local agency criteria where there are conflicts with the MDT design criteria. Decisions to use local agency criteria should be made by the design team on a case‐by‐case basis. Chapter 2 of the MDT Road Design Manual outlines the basic design controls for the criteria presented in this document. Page 2 MDT Geometric Design Standards This page intentionally left blank. MDT Geometric Design Standards Page 3 The design criteria summary tables are intended to provide a resource for the design team to have a concise listing of design values. However, the design team should review Chapter 2 of the RDM and additional RDM section references for more information on the design elements. In addition, the tables include footnotes, which are identified by a number in parentheses (e.g., (6)) and are critical to the proper use of the design tables. 1.1 Route Segment Plan The Route Segment Plan is based on functional classification, traffic volumes, and route continuity. The purpose is to identify and define a consistent pavement width to be used when reconstruction or major widening is conducted on a route segment. For NHS roadways, the criteria provided in the AASHTO Green Book and the supplemental A Policy on Design Standards Interstate System set the minimum standards (1, 2). The MDT Route Segment Plan Map is provided at the following link on the MDT Website. MDT Route Segment Plan Map Chapters 2 and 5 of the RDM provide additional information regarding the roadway width decision process for MDT. Additional roadway width design information for various types of facilities can be found in the AASHTO Green Book and the Guidelines for Nomination and Development of Pavement Projects (1, 3). Page 6 MDT Geometric Design Standards 2.2 Rural Principal Arterials (NHS ‐ Non Interstate) Exhibit 2 Geometric Design Criteria for Rural Principal Arterials (NHS - Non Interstate) Design Element RDM Section Design Criteria D es ig n C o n tr o l Design Speed (minimum) Level 2.5 70 mph Rolling 60 mph Mountainous 50 mph R o ad w ay E le m en ts Travel Lane Width 5.2 12 ft (1) Shoulder Width 5.2 Varies (1) Cross Slope Travel Lane 5.2 2% Shoulder 2% Median Width 5.3 Varies (2) C u t S ec ti o n s Ditch Inslope 5.4 6:1 (Width: 10 ft) Width 5.4 10 ft Min. Slope 20:1 towards backslope Backslope Cut Depth at Slope Stake (3) 0 – 5 ft 5.4 5:1 5 – 10 ft Level/Rolling: 4:1; Mountainous: 3:1 10 – 15 ft Level/Rolling: 3:1; Mountainous: 2:1 15 – 20 ft Level/Rolling: 2:1; Mountainous: 1.5:1 > 20 ft 1.5:1 F ill S lo p es Fill Height at Slope Stake (4) 0 – 10 ft 5.4 6:1 10 – 20 ft 4:1 20 – 30 ft 3:1 > 30 ft 2:1 A lig n m en t E le m en ts DESIGN SPEED 2.5 70 mph 60 mph 50 mph Stopping Sight Distance 2.8 730 ft 570 ft 425 ft Passing Sight Distance 2.8 1,200 ft 1000 ft 800 ft Minimum Radius (e=8.0%) 3.2 1,810 ft 1,200 ft 760 ft Spiral Curve Selection See Chapter 3, Section 3.2 of the RDM Superelevation Rate (5) 3.3 emax = 8.0% Vertical Curve Length Crest See Chapter 4, Section 4.4 of the RDM Sag Maximum Grade Level 4.3 3% Rolling 4% Mountainous 7% Minimum Vertical Clearance (6) 4.5 17.0 ft MDT Geometric Design Standards Page 7 Rural Principal Arterials (NHS ‐ Non Interstate) Footnotes 1. Travel Lane/Shoulder Width. Roadway width is based on the Route Segment Map described in Section 1.1 or the AASHTO Green Book standards, whichever value is more conservative. The AASHTO Green Book provides values for minimum width of traveled way and usable shoulder for rural arterials. 2. Median Width. For two‐way, left‐turn lanes in rural conditions, the minimum width is 14 feet. See Chapter 5, Section 5.3 of the RDM for additional information on median widths. 3. Cut Slopes (Rock). The backslope through rock cut sections will be determined by the Geotechnical Section based on its field investigation. 4. Fill Slopes (Rock). In rock fills over 10 feet high, the typical fill slope is 1.5:1. In rock fills less than or equal to 10 feet, the typical slope is 6:1. 5. Superelevation Rate. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. 6. Minimum Vertical Clearance. The clearances apply to the arterial passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays. Page 8 MDT Geometric Design Standards 2.3 Rural Minor Arterials (Non‐NHS Primary) Exhibit 3 Geometric Design Criteria for Rural Minor Arterials Design Element RDM Section Design Criteria D es ig n C o n tr o l Design Speed Level 2.5 60 mph Rolling 55 mph Mountainous 45 mph R o ad w ay E le m en ts Travel Lane Width 5.2 12 ft (1) Shoulder Width 5.2 Varies (1) Cross Slope Travel Lane 5.2 2% Shoulder 2% Median Width 5.3 Varies (2) C u t S ec ti o n s Ditch Inslope 5.4 6:1 (Width: 10 ft) Width 5.4 10 ft Min. Slope 20:1 towards backslope Backslope Cut Depth at Slope Stake (3) 0 – 5 ft 5.4 5:1 5 – 10 ft Level/Rolling: 4:1; Mountainous: 3:1 10 – 15 ft Level/Rolling: 3:1; Mountainous: 2:1 15 – 20 ft Level/Rolling: 2:1; Mountainous: 1.5:1 > 20 ft 1.5:1 F ill S lo p es Fill Height at Slope Stake (4) 0 – 10 ft 5.4 6:1 10 – 20 ft 4:1 20 – 30 ft 3:1 > 30 ft 2:1 A lig n m en t E le m en ts DESIGN SPEED 2.5 60 mph 55 mph 45 mph Stopping Sight Distance 2.8 570 ft 495 ft 360 ft Passing Sight Distance 2.8 1,000 ft 900 ft 700 ft Minimum Radius (e=8.0%) 3.2 1,200 ft 960 ft 590 ft Spiral Curve Selection See Chapter 3, Section 3.2 of the RDM Superelevation Rate (5) 3.3 emax = 8.0% Vertical Curve Length Crest See Chapter 4, Section 4.4 of the RDM Sag Maximum Grade Level 4.3 3% Rolling 4% Mountainous 7% Minimum Vertical Clearance (6) 4.5 17.0 ft MDT Geometric Design Standards Page 11 Rural Collector Roads Footnotes 1. Median Width. For two‐way, left‐turn lanes in rural conditions, the minimum width is 14 feet. See Chapter 5, Section 5.3 of the RDM for additional information on median widths. 2. Ditch. A V‐ditch may be used with an approved design exception. For backslopes steeper than 4:1, place the toe of the backslope outside the clear zone. 3. Cut Slopes. The design team should attempt to locate backslopes steeper than 4:1 outside the clear zone. The backslope through rock cut sections will be determined by the Geotechnical Section based on its field investigation. At a maximum, the backslope typically will not exceed 0.25:1. For large cuts, benching of the backslope may be required. 4. Fill Slopes (Rock). In rock fills over 10 feet high, the typical fill slope is 1.5:1. In rock fills less than or equal to 10 feet, the typical slope is 6:1. 5. Superelevation Rate. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. 6. Minimum Vertical Clearance. The clearances apply to the collector passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays. Page 12 MDT Geometric Design Standards 2.5 Guidance for Rural Local Roads Exhibit 5 Guidance for Rural Local Roads Design Element RDM Section Design Criteria D es ig n C o n tr o ls Current AADT 2.6 ≤ 300 (1) Design Speed Paved Surface 2.5 50 mph (2) Gravel Surface 45 mph (2) R o ad w ay E le m en ts Minimum Roadway Width 5.2 24 ft (3) Cross Slope Travel Lane 5.2 Paved: 2% Gravel: 3% Shoulder Paved: 2% Gravel: 3% Median Width 5.3 Varies (4) C u t S ec ti o n s Inslope 5.4 4:1 Ditch (5) 5.4 V-Ditch (1.5 ft Depth) Backslope Cut Depth at Slope Stake (6) 0 – 5 ft 5.4 4:1 5 – 10 ft Level/Rolling: 3:1; Mountainous: 2:1 10 – 15 ft Level/Rolling: 2:1; Mountainous: 1.5:1 > 15 ft 1.5:1 F ill S lo p es Fill Height at Slope Stake (7) 0 – 10 ft 5.4 4:1 10 – 20 ft 3:1 > 20 ft 1.5:1 A lig n m en t E le m en ts DESIGN SPEED 2.5 50 mph 45 mph 30 mph(2) Stopping Sight Distance 2.8 425 ft 360 ft 200 ft Passing Sight Distance 2.8 800 ft 700 ft 500 ft Minimum Radius 3.2 760 ft 560 ft 205 ft Spiral Curve Selection 3.2 e ≥ 7% N/A N/A Superelevation Rate (8) 3.3 emax = 8.0% emax = 4% emax = 4% Vertical Curve Length Crest See Chapter 4, Section 4.4 of the RDM Sag Maximum Grade Level 4.3 6% 7% 7% Rolling 8% 9% 10% Mountain ous 10% 10% 10% Minimum Vertical Clearance (9) 4.5 14.5 ft MDT Geometric Design Standards Page 13 Rural Local Roads Footnotes 1. AADT. For local rural roads with current AADT > 300 and/or functionally classified as a rural collector, the design criteria for rural collector roads should be used (Exhibit 4). For local roads with current AADT ≤ 300 design the project using one of the following: a. County standards – note that many counties do not have standards b. The design criteria provided in Exhibit 5 c. AASHTO’s Guidelines for Geometric Design of Very Low‐Volume Local Roads (4). Use these guidelines only if it is not practical to meet the criteria in Exhibit 5. 2. Design Speed. See Chapter 2, Section 2.5 of the RDM for selection of design speed. For local roads requiring a higher design speed, the criteria for rural collector roads should be used (Exhibit 4). A 30 mph design speed may be used, but only if the adjacent terrain presents obstacles that render the use of a higher design speed impractical. A formal design exception for design speed is not required for rural local roads. However, deviation from the design speeds in Exhibit 5 must be documented in the PFR, AGR and SOW reports. 3. Roadway Width. The bridge width, adjacent paved traveled way width and county standards should be considered when establishing a roadway width, if greater than the minimum. Bridges will typically provide a minimum roadway width of 28 feet. This width should be utilized to the end of the approach guardrail. 4. Median Width. For two‐way, left‐turn lanes in rural conditions, the minimum width is 14 feet. See Chapter 5, Section 5.3 of the RDM for additional information on median widths. 5. Ditch. V‐ditches can be used without prior approval. The design team should attempt to make the ditch traversable or locate it outside of the clear zone. 6. Cut Slopes (Rock). The backslope through rock cut sections will be determined by the Geotechnical Section based on its field investigation. 7. Fill Slopes. In rock fills over 10 feet high, the typical fill slope is 1.5:1. In rock fills less than or equal to 10 feet, the typical fill slope is 4:1. In earth fills where the fill depth greater than 20 feet, the use of steeper than 1.5:1 slopes may be used if justified by a slope stability analysis. 8. Superelevation Rate. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. Refer to AASHTO’s Guidelines for Geometric Design of Very Low‐Volume Local Roads (4) and assume 5 mph reduction in design speed for determining superelevation for design speeds 45 mph or less. 9. Minimum Vertical Clearance. The clearances apply to the local road passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays. Page 16 MDT Geometric Design Standards 3.3 Urban Freeways (NHS ‐ Interstate) Design Element RDM Section Design Criteria D es ig n C o n tr o l Design Speed (minimum) Level 2.5 50 mph Rolling Mountainous R o ad w ay E le m en ts Minimum Number of Travel Lanes 5.2 4 (minimum of 2 in each direction) Travel Lane Width 5.2 12 ft Shoulder Width Outside Shoulder 5.2 10 ft (1) Inside Shoulder 4 ft (2) Cross Slope Travel Lane 5.2 2% Shoulder 2% (3) Median Width Level 5.3 Minimum: 16 ft (4) Rolling Mountainous C u t S ec ti o n s(5 ) Ditch Inslope 5.4 6:1 (Width: 6 ft) Width 5.4 10 ft Slope 20:1 towards backslope Backslope Cut Depth at Slope Stake (6) 0 – 5 ft 5.4 5:1 5 – 10 ft 3:1 10 – 15 ft 2:1 > 15 ft 1.5:1 F ill S lo p es (5 ) Fill Height at Slope Stake (7) 0 – 10 ft 5.4 6:1 10 – 20 ft 4:1 20 – 30 ft 3:1 > 30 ft 2:1 A lig n m en t E le m en ts DESIGN SPEED 2.5 50 mph Stopping Sight Distance 2.8 425 ft Minimum Radius (e = 8.0%) 3.2 760 ft Spiral Curve Selection See Chapter 3, Section 3.2 of the RDM Superelevation Rate (8) 3.3 emax = 8.0% Vertical Curve Length Crest See Chapter 4, Section 4.4 of the RDM Sag Maximum Grade(9) Level 4.3 4% Rolling 5% Mountainous 6% Minimum Vertical Clearance (10) 4.5 17.0 ft Exhibit 7 Geometric Design Criteria for Urban Freeways (NHS - Interstate) MDT Geometric Design Standards Page 17 Urban Freeways (NHS ‐ Interstate) Footnotes 1. Outside Shoulder Width. In mountainous terrain, these may be reduced to a minimum width of 8 feet where costs would be prohibitive to provide wider shoulders. 2. Inside Shoulder Width. The following apply: a. For 3 or more through lanes in one direction, inside shoulders shall be 10 feet wide. b. Where continuous curbs are used in narrow medians on ramps, the inside shoulder width should desirably be 2 feet and a minimum of 1 foot. c. Where vertical elements (other than abutments, piers or walls) in the median are more than 1 foot high, the minimum offset from the edge of travel lane to the element is 4 feet. 3. Shoulder Cross Slope. Existing shoulder slopes on existing freeways may be 3.75 percent. If the proposed pavement work is resurfacing, the existing 3.75 percent slope may be retained. If the proposed pavement work is full‐depth reconstruction or major rehabilitation, the shoulder slope should match the cross slope of the traveled way, typically 2 percent. 4. Minimum Median Width. The minimum median width of 10 feet may be used in urban areas with high right‐of‐way costs and in rugged mountainous terrain. It may also be used on any long and unusually costly bridges. The minimum median width should be the width of the two inside shoulders and the width of the base of the barrier. 5. The design information for cut and fill slopes are intended to provide design guidance and are not MDT standards 6. Cut Slopes (Rock). The backslope through rock cut sections will be determined by the Geotechnical Section based on its field investigation. At a maximum, the backslope typically will not exceed 0.25:1. For large cuts, benching of the backslope may be required. 7. Fill Slopes (Rock). In rock fills over 10 feet high, the typical fill slope is 1.5:1. In rock fills less than or equal to 10 feet, the typical slope is 6:1. 8. Superelevation Rate. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. 9. Maximum Grade (Level, Rolling, and Mountainous). Grades 1% steeper than the value shown may be provided in urban areas with right‐of‐way constraints or where needed in mountainous terrain. 10. Minimum Vertical Clearance. The clearances apply to a freeway passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays. Page 18 MDT Geometric Design Standards 3.4 Urban Principal Arterials (NHS ‐ Non Interstate) (1) Design Element RDM Section Curbed Shouldered D es ig n C o n tr o l Design Speed (2) 2.5 40 mph 40 mph R o ad w ay E le m en ts Travel Lane Width(3) 5.2 12 ft Minimum Roadway Width 5.2 28 ft (4) 36 ft Shoulder Width Outside 5.2 0 6 ft Inside N/A Cross Slope Travel Lane 5.2 2% Typical (5) 2% Shoulder 2% Typical (5) 2% Minimum Median Width 5.3 Raised: 4 ft (6) TWLTL Width (7) 5.2 12 ft Bicycle Lane Width (8) 5.2 4 ft Parking Lane Width (9) 5.2 10 ft (10) N/A C u t S ec ti o n Ditch Slope (11) 5.4 4:1 A lig n m en t E le m en ts (1 6) DESIGN SPEED 2.5 40 mph Stopping Sight Distance (12) 2.8 305 ft Intersection Sight Distance (13) 2.8 195 ft Minimum Radius 3.2 533 ft Superelevation Rate (14) 3.3 emax = 4.0% Vertical Curve Length Crest See Chapter 4, Section 4.4 of the RDM Sag Maximum Grade Level 4.3 6% Rolling 7% Mountainous 9% Minimum Vertical Clearance (15) 4.5 17.0 ft Exhibit 8 Geometric Design Criteria for Urban Principal Arterials (NHS — Non Interstate) MDT Geometric Design Standards Page 21 Urban Minor Arterials Footnotes 1. Federal functional classification defined by MDT and approved by the Montana Transportation Commission and the FHWA. 2. The design speed for urban minor arterials should match the conditions and driver expectancy. In the transitional areas between rural and urban sections of roadway, the use of the criteria for rural minor arterials may be appropriate. However, the determination of the design speed for transitional areas should be based on consideration of roadside development, number and type of approaches, lane configuration and traffic control devices. 3. For multilane facilities, the interior and exterior lane width is 11 feet. 4. The lane width does not include the gutter section. Add three feet where wide curb lane is provided for accommodating bicycles. 5. Cross Slopes (Curbed). The cross slope may be between 1‐percent and 4‐ percent, depending on site conditions. 6. The raised median width needs to be added to the exclusive left‐turn lane width. See Chapter 5, Section 5.3 of the RDM for additional information on median width. 7. This is also applicable for an exclusive left‐turn lane with a flush median. 8. The bicycle lane width can include the shoulder width if there is no parking. A 5‐foot width is recommended from the face of curb, guardrail or other roadside barriers. An increased lane width is recommended where the percentage of trucks or buses is high. See the AASHTO Guide for the Development of Bicycle Facilities for additional information (7). 9. Includes the width of the gutter section. 10. 8 feet may be acceptable when the lane is not likely to become a traffic lane in the foreseeable future. 11. Slopes steeper than 4:1 should be used only when achieving a 4:1 slope is not feasible. The preferred ditch width is 10 feet. However, site constraints often make the use of this width not feasible. If the use of a v‐ ditch is necessary, it should be traversable or the hinge point should be located outside of the clear zone. A design exception is required for the use of a narrower ditch. 12. The stopping sight distance must be adjusted for higher design speeds and grades. See Chapter 2, Section 2.8 of the RDM and the AASHTO Green Book for additional information (1). 13. See Chapter 2, Section 2.8 of the RDM and the AASHTO Green Book (1). 14. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. 15. The clearances apply to the arterial passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays. Page 22 MDT Geometric Design Standards 3.6 Urban Collector Streets (1) Design Element Manual Section Design Criteria Curbed Shouldered D es ig n C o n tr o l Design Speed (2) 2.5 30 mph 30 mph R o ad w ay E le m en ts Travel Lane Width 5.2 10 ft (3) Shoulder Width Outside 5.2 0 ft 4 ft (4) Inside N/A Cross Slope Travel 5.2 2% Typical (5) 2% Shoulder 2% Typical (5) 2% Minimum Median Width 5.3 Raised: 4 ft (6) TWLTL Width (7) 5.2 11 ft Bicycle Lane Width (8) 5.2 4 ft Parking Lane Width (9) 5.2 8 ft E ar th C u t S ec ti o n Ditch Slope (10) 5.4 4:1 A lig n m en t E le m en ts (1 5) DESIGN SPEED 2.5 30 mph Stopping Sight Distance (11) 2.8 200 ft Intersection Sight Distance (12) 2.8 140 ft Minimum Radius (@ emax = 4%) 3.2 250 ft Spiral Curve Selection See Chapter 3, Section 3.2 Superelevation Rate (13) 3.3 emax = 4.0% Vertical Curve Length Crest See Chapter 4, Section 4.4 Sag Maximum Grade Level 4.3 9% Rolling 10% Mt 10% Minimum Vertical Clearance (14) 4.5 16.5’ Mt: Mountainous Exhibit 10 Geometric Design Criteria for Urban Collector Streets MDT Geometric Design Standards Page 23 Urban Collector Streets Footnotes 1. Federal functional classification defined by MDT and approved by the Montana Transportation Commission and the FHWA. 2. The design speed for urban collectors should match the conditions and driver expectancy. In the transitional areas between rural and urban sections of roadway, the use of the criteria for rural collectors may be appropriate. However, the determination of the design speed for transitional areas should be based on consideration of roadside development, number and type of approaches, lane configuration and traffic control devices. 3. The lane width does not include the gutter section. Add three feet where wide curb lane is provided for accommodating bicycles. 4. Shouldered cross‐section only. 5. Cross Slopes (Curbed). The cross slope may be between 1‐percent and 4‐ percent, depending on site conditions. 6. The raised median width needs to be added to the exclusive left‐turn lane width. See Chapter 5, Section 5.3 of the RDM for additional information on median width. 7. This is also applicable for an exclusive left‐turn lane with a flush median. For exclusive turn lanes, use 11 feet for collectors that primarily serve commercial/industrial areas. 8. The bicycle lane width can include the shoulder width if there is no parking. A 5‐foot width is recommended from the face of curb, guardrail or other roadside barriers. An increased lane width is recommended where the percentage of trucks or buses is high. See the AASHTO Guide for the Development of Bicycle Facilities for additional information (7). 9. Includes the width of the gutter section. 10. Slopes steeper than 4:1 should be used only when achieving a 4:1 slope is not feasible. The preferred ditch width is 10 feet. However, site constraints often make the use of this width not feasible. If the use of a v‐ ditch is necessary, it should be traversable or the hinge point should be located outside of the clear zone. A design exception is required for the use of a narrower ditch. 11. See Chapter 2, Section 2.8 of the RDM and the AASHTO Green Book for additional information regarding stopping sight distance (1). 12. See Chapter 2, Section 2.8 of the RDM and the AASHTO Green Book for additional information (1). 13. See Chapter 3, Section 3.3 of the RDM for superelevation rates based on design speed and curve radii. 14. The clearances apply to the collector passing under a bridge. The minimum clearance includes a 6‐inch additional allowance for future overlays.