PDDM Chapter 9 - Highway Design

1 Highway Design August 2012 Table of Contents 9-i Chapter 9 Highway Design TABLE OF CONTENTS GENERAL ..9-1 Role of the Designer ..9-1 Design Requirements and Standards ..9-4 Exceptions to Design Standards ..9-4 Need for Design Exception ..9-6 Design Exception Consequences and Risk Assessment ..9-7 Mitigating Design Exceptions ..9-8 Documenting Design Exceptions ..9-8 Monitoring Design Exceptions ..9-8 Variances to FLH Standard Practice and Guidance ..9-9 Design Philosophy and Context Sensitive Solutions ..9-9 GUIDANCE AND REFERENCES .. 9-12 Standards of Practice .. 9-12 9-13 GEOMETRIC Design .. 9-16 Geometric Design Controls .. 9-16 Roadway Context .. 9- 16 Functional 9-17 Terrain .. 9-19 Location .. 9-20 Traffic Volume .. 9-20 Level of Service and Mobility.

2 9-22 Level of Access and Management .. 9-22 Cross Section and Multi-modal Accommodation .. 9-22 Design Vehicle .. 9-23 User Characteristics .. 9-25 Maximum and Minimum Superelevation Rate .. 9-26 Speed Characteristics .. 9-27 Selecting an Appropriate Design Speed .. 9-29 Self-explaining, Self-enforcing Road Concepts .. 9-33 Aesthetic Considerations .. 9-34 Horizontal and Vertical Alignment Relationships .. 9-35 Combinations of Design Elements and Features .. 9-35 Human Factors and Driver Performance .. 9-36 Design Consistency .. 9-36 Combinations of Design Elements with Intersections and Bridges .. 9-37 Additive Design Risk Assessment .. 9-37 Horizontal Alignment .. 9-37 Horizontal Curves .. 9-38 Horizontal Curve and Superelevation Transitions .. 9-41 Risk Assessment and 9-52 Vertical Alignment.

3 9-53 Highway Design August 2012 TABLE OF CONTENTS (Continued) 9- ii Table of Contents Vertical Curves .. 9-54 Maximum Grade .. 9-54 Minimum Grade .. 9-55 Critical Lengths of 9-56 Intersection Considerations .. 9-56 Hidden Dips .. 9-56 Switchbacks .. 9-56 Drainage Considerations .. 9-57 Vertical Clearance .. 9-57 Risk Assessment and 9-58 Sight Distance .. 9-58 Determination of Sight Distance Requirements .. 9-59 Stopping Sight Distance .. 9-60 Decision Sight Distance .. 9-60 Passing Sight Distance .. 9-60 Intersection Sight Distance .. 9-61 Limiting Conditions and Restrictions .. 9-63 Risk Assessment and 9-64 Geometric Cross Section .. 9-66 Traveled Way (Lane) Width .. 9-66 Shoulder Width and Type .. 9-67 Horizontal Clearance to Structures .. 9-69 Cross Slope.

4 9-69 Pavements and Geometric Design Considerations .. 9-70 Risk Assessment and 9-71 Roadway Widening .. 9-71 Traveled Way Widening on Curves .. 9-71 Auxiliary Lanes .. 9-72 Parking Lanes .. 9-72 Speed Change and Turning Lanes .. 9-74 Climbing Lanes .. 9-74 Passing Zones and Lanes .. 9-75 Bicycle Lanes .. 9-78 Slow Moving Vehicle Turnouts .. 9-78 Parking Pullouts .. 9-79 Shoulder Widening for Barriers .. 9-80 Medians .. 9-80 Benefits and Disadvantages of Medians .. 9-80 Urban Medians .. 9-81 Rural Medians .. 9-81 Variable Medians and Independent Alignments .. 9-82 Curbs .. 9-82 Vertical Curbs .. 9-84 Sloping Curbs .. 9-84 Curb Offsets .. 9-84 Accessibility Issues with Curbing .. 9-85 Roadside Design Considerations .. 9-85 Forgiving Roadside Concepts .. 9-86 Clear Zone.

5 9-86 Lateral Clearance and Offset Distance .. 9-87 Highway Design August 2012 TABLE OF CONTENTS (Continued) Table of Contents 9- iii Considerations for Existing Features .. 9-88 Access Management .. 9-88 Driveways .. 9-88 Foreslopes .. 9-89 Recoverable Foreslopes .. 9-89 Traversable Foreslopes .. 9-90 Pavement Edge Transitions .. 9-90 Pavement Drainage Considerations .. 9-90 Foreslope Considerations at Intersections .. 9-90 Design of Intersections .. 9-91 Intersection Characteristics .. 9-91 Intersection Types .. 9-92 Intersection Design Vehicle .. 9-92 Intersection Alignment .. 9-93 Left-Turn Lanes .. 9-96 Right-turn Lanes .. 9-99 Bypass Lanes .. 9-103 Channelization .. 9-104 Islands .. 9-105 Pedestrian, Bicyclist and Transit Considerations at Intersections .. 9- 106 9-107 Railroad- Highway Grade Crossings.

6 9-108 Pedestrian Considerations and Facilities .. 9-110 Sidewalks .. 9-111 Walking and Hiking Trails .. 9-112 Accommodation of the Disabled .. 9-113 Bicycle Considerations and Facilities .. 9-114 Transit Considerations and Facilities .. 9-116 Parking Lot Layout Considerations .. 9-116 RESURFACING, RESTORATION AND REHABILITATION (RRR) Design .. 9-118 Application of Design Standards .. 9-118 Improvement of Safety Performance .. 9-118 Evaluation of Existing Geometric Design .. 9-119 Improvement of Roadside Conditions .. 9-121 Improvement of Traffic Operations .. 9-122 Evaluation of Pavement and Drainage Structures .. 9-123 Mitigation of Substandard Design Features .. 9-123 OTHER Highway Design ELEMENTS .. 9-125 Earthwork Design .. 9-125 Clearing and Grubbing .. 9-125 Removal of Structures and Obstructions.

7 9-126 Design of Excavation and Embankment .. 9-126 Determination of Excavation and Embankment Volumes .. 9-127 Balancing Earthwork .. 9-127 Highway Design August 2012 TABLE OF CONTENTS (Continued) 9- iv Table of Contents Haul .. 9-128 Mass Diagram .. 9-128 Borrow and Offsite Borrow Areas .. 9-128 Waste and Offsite Waste Areas .. 9-128 Rock Blasting .. 9-128 Watering and Water Sources .. 9-128 Structural Excavation and Backfill .. 9-129 Conservation of 9-129 Roadway Obliteration .. 9-129 Linear Grading .. 9-129 Subgrade Treatments and Stabilization .. 9-129 Slope Treatments .. 9-131 Safety Considerations .. 9-131 Geotechnical Considerations .. 9-131 Grading Techniques .. 9-131 Slope Waterways and Catchment Basins .. 9-136 Rock Cut Slopes .. 9-136 Slides and Slope Stabilization.

8 9-137 Slope Protection .. 9- 137 Earth Retaining Structures .. 9-137 Determination of Need .. 9-137 Alternative Wall 9-138 Selection of a Retaining Wall System .. 9-138 Retaining Wall Systems .. 9-138 Geometric Information for Design of Retaining Wall Systems .. 9-139 Landscaping and Restoration of Vegetation .. 9-140 Enhanced Clearing Techniques .. 9-140 Enhanced Grading Techniques .. 9-140 Enhanced Rock Work .. 9-142 Topsoil 9-142 Restoration of Vegetation .. 9-143 Landscape Planting .. 9-143 Slope Enhancements .. 9-144 Ornamental Landscapes .. 9-144 Drainage Design .. 9-144 Safety Considerations .. 9-145 Roadway Ditches and Channels .. 9-145 Culverts .. 9-147 Pavement Drainage .. 9-148 Downdrains and Pipe Anchors .. 9-149 Storm Drains .. 9-149 Underdrains and Horizontal Drains.

9 9-149 Riprap Slope Protection .. 9-149 Energy Dissipators and Outlet Detention Basins .. 9-149 Soil Erosion and Sediment Control .. 9-150 Developing Erosion and Sediment Control Plans .. 9-150 Erosion and Sediment Control Phases .. 9-151 Parking and Rest Areas .. 9-152 Roadway Appurtenances .. 9-153 Highway Design August 2012 TABLE OF CONTENTS (Continued) Table of Contents 9-v Highway Lighting Systems .. 9-153 Fencing .. 9-153 Cattle Guards .. 9-155 Right-of-Way and Utility Considerations .. 9-155 Environmental Protection and Enhancements .. 9-156 Construction Considerations .. 9-157 Construction Sequencing .. 9-157 Constructability .. 9-157 PLANS SPECIFICATIONS AND ESTIMATE (PS&E) DEVELOPMENT .. 9-158 PS&E Package .. 9-158 Alternative PS&E Development and Contracting Options.

10 9-158 PS&E Development at Various Stages of Design .. 9-159 Conceptual Studies and Preliminary 9-159 Intermediate Design .. 9-159 Intermediate Design Revisions .. 9-160 Plan-in-Hand (PIH) PS&E .. 9-161 Final Design .. 9-162 Reviews .. 9-162 Preliminary Design (15 or 30 Percent) Review .. 9-163 Intermediate Design (50 Percent) Review .. 9-164 Plan-In-Hand Design (70 Percent) Review .. 9-165 Final PS&E (95 Percent) Review .. 9-166 PS&E Approval and Authorization (100 Percent) .. 9-166 Value Engineering .. 9-167 Plans .. 9-168 Format .. 9-168 Drafting Standards .. 9-169 Organization of Plans .. 9-170 FLH Standard Drawings, Division Standard Details and Special Details .. 9-181 Supporting Information .. 9-183 Computation of Quantities .. 9-183 Design Documentation.