Policy on Geometric Design of Highways And Streets

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Policy on Geometric Design of Highways And Streets


Table of Contents
Preface 
Foreword

CHAPTER TITLES

Chapter  1  Highway Functions
Chapter  2  Design Controls and Criteria
Chapter  3  Elements of Design
Chapter  4  Cross Section Elements
Chapter  5  Local Roads and Streets
Chapter  6  Collector Roads and Streets
Chapter  7  Rural and Urban Arterials
Chapter  8  Freeways 
Chapter  9  Intersections 
Chapter  10  Grade Separations and Interchanges

Chapter 1 HIGHWAY FUNCTIONS

Systems and Classifications...............1
The Concept of Functional Classification .......................1
Hierarchies of Movements and Components............1
Functional Relationships............4
Access Needs and Controls ........6
Functional System Characteristics......7
Definitions of Urban and Rural Areas.....................7
Functional Categories................8
Functional Systems for Rural Areas........................8
Rural Principal Arterial System.......................8
Rural Minor Arterial System...........................9
Rural Collector System.......9
Rural Local Road System...9
Extent of Rural Systems ... 10
Functional Highway Systems in Urbanized Areas . 10
Urban Principal Arterial System....................10
Urban Minor Arterial Street System..............11
Urban Collector Street System......................12
Urban Local Street System...........................12
Length of Roadway and Travel on Urban Systems .......................12
Functional Classification as a Design Type ........... 13
References....... 14

Chapter 2 DESIGN CONTROLS AND CRITERIA

Introduction...... 15
Design Vehicles 15
General Characteristics............ 15
Minimum Turning Paths of Design Vehicles......... 18
Vehicle Performance ............... 43
Vehicular Pollution.................. 43
Driver Performance........................ 46
Introduction 46
Older Drivers.......................... 47
The Driving Task.................... 47
The Guidance Task................. 48
Lane Placement and Road Following.............48
Car Following..................48
Passing Maneuvers...........49
Other Guidance Activities.49
The Information System........... 49
Traffic Control Devices....49
The Roadway and its Environment................49
Information Handling............... 50
Reaction Time..................50
Primacy...........................53
Expectancy......................53
Driver Error  53
Errors Due to Driver Deficiencies .................54
Errors Due to Situation Demands ..................56
Speed and Design.................... 56
Design Assessment.................. 57
Traffic Characteristics.............. 58
General Considerations.....58
Volume..... 58
Average Daily Traffic.......58
Peak-Hour Traffic ............59
Directional Distribution........... 62
Composition of Traffic ............ 63
Projection of Future Traffic Demands................... 65
Speed....... 66
Operating Speed...............66
Running Speed.................67
Design Speed...................67
Traffic Flow Relationships ....... 72
Highway Capacity .......................... 74
General Characteristics............ 74
Application . 74xiii
Capacity as a Design Control.... 75
Design Service Flow Rate Versus Design Volume........................75
Measures of Congestion....75
Relation Between Congestion and Traffic Flow Rate....................76
Acceptable Degrees of Congestion ................77
Principles for Acceptable Degrees of Congestion..........................78
Reconciliation of Principles for Acceptable Degrees of Congestion ...........................80
Factors Other Than Traffic Volume That Affect Operating Conditions.. 81
Highway Factors..............81
Alignment........................82
Weaving Sections.............82
Ramp Terminals...............82
Traffic Factors.................83
Peak Hour Factor .............83
Levels of Service..................... 84
Design Service Flow Rates ...... 85
Weaving Sections.............85
Multilane Highways Without Access Control.86
Arterial Streets and Urban Highways.............86
Intersections.....................88
Pedestrians and Bicycles...88
Access Control and Access Management ..................... 88
General Conditions.................. 88
Basic Principles of Access Management............... 90
Access Classifications.............. 90
Methods of Controlling Access 91
Benefits of Controlling Access. 91
The Pedestrian.. 96
General Considerations ............ 96
General Characteristics............ 96
Walking Speeds ...................... 97
Walkway Capacities................ 98
Sidewalks ........................98
Intersections.....................99
Reducing Pedestrian-Vehicular Conflicts.......99
Characteristics of Persons With Disabilities .......... 99
Mobility Impairments..... 100
Visual Impairments........ 100
Developmental Impairments ....................... 100
Bicycle Facilities.......................... 100
Safety............ 101
Environment... 106
Economic Analysis ....................... 106
References..... 106xiv

Chapter 3 ELEMENTS OF DESIGN

Introduction.... 109
Sight Distance 109
General Considerations .......... 109
Stopping Sight Distance......... 110
Brake Reaction Time...... 110
Braking Distance ........... 111
Design Values................ 113
Effect of Grade on Stopping........................ 113
Variation for Trucks ....... 114
Decision Sight Distance......... 115
Passing Sight Distance for Two-Lane Highways.. 118
Criteria for Design.......... 118
Design Values................ 122
Effect of Grade on Passing Sight Distance... 125
Frequency and Length of Passing Sections... 125
Sight Distance for Multilane Highways............... 126
Criteria for Measuring Sight Distance................. 127
Height of Driver’s Eye ... 127
Height of Object............ 127
Sight Obstructions.......... 128
Measuring and Recording Sight Distance on Plans ..................... 128
Horizontal Alignment.................... 131
Theoretical Considerations..... 131
General Considerations .......... 132
Superelevation ............... 132
Side Friction Factor........ 133
Distribution of e and f Over a Range of Curves.......................... 138
Design Considerations ........... 141
Maximum Superelevation Rates.................. 141
Minimum Radius............ 142
Design for Rural Highways, Urban Freeways, and High-Speed Urban Streets.......... 143
Procedure for Development of Finalized e Distribution............... 146
Design Superelevation Tables..................... 155
Sharpest Curve Without Superelevation....... 166
Effects of Grades........... 167
Transition Design Controls..... 168
General Considerations... 168
Tangent-to-Curve Transition....................... 169
Spiral Curve Transitions . 176
Length of Spiral............. 177
Compound Curve Transition....................... 184
Methods of Attaining Superelevation........... 184
Design of Smooth Profiles for Traveled Way Edges................... 187xv
Axis of Rotation with a Median................... 188
Minimum Transition Grades....................... 190
Turning Roadway Design....... 191
Design for Low-Speed Urban Streets.................. 192
Maximum Comfortable Speed on Horizontal Curves.................. 195
Minimum Superelevation Runoff Length..... 195
Minimum Radii and Minimum Lengths of Superelevation Runoff for
Limiting Values of e and f .......................... 198
Curvature of Turning Roadways and Curvature at Intersections.......... 198
Minimum Radius for Turning Speed............ 198
Transitions and Compound Curves.............. 203
Length of Spiral............. 203
Compound Circular Curves ........................ 205
Offtracking 206
Derivation of Design Values for Widening on Horizontal Curves 206
Traveled Way Widening on Horizontal Curves.... 212
Design Values for Traveled Way Widening.. 214
Application of Widening on Curves............. 218
Widths for Turning Roadways at Intersections..... 220
Design Values................ 223
Widths Outside Traveled Way.................... 226
Sight Distance on Horizontal Curves .................. 228
Stopping Sight Distance . 228
Passing Sight Distance ... 232
General Controls for Horizontal Alignment......... 233
Vertical Alignment ....................... 235
Terrain.... 235
Grades.... 235
Vehicle Operating Characteristics on Grades . 236
Control Grades for Design .......................... 239
Critical Lengths of Grade for Design........... 242
Climbing Lanes..................... 247
Climbing Lanes for Two-Lane Highways .... 247
Climbing Lanes on Freeways and Multilane Highways............... 251
Methods for Increasing Passing Opportunities on  Two-Lane Roads... 254
Passing Lanes................ 254
Turnouts........................ 257
Shoulder Driving............ 258
Shoulder Use Sections .... 259
Emergency Escape Ramps ..... 259
General.......................... 259
Need and Location for Emergency Escape Ramps...................... 261
Types of Emergency Escape Ramps ............ 262
Design Considerations.... 264
Brake Check Areas ........ 268
Maintenance.................. 268xvi
Vertical Curves..................... 269
General Considerations... 269
Crest Vertical Curves..... 270
Sag Vertical Curves ....... 276
Sight Distance at Undercrossings ................ 280
General Controls for Vertical Alignment...... 282
Combinations of Horizontal and Vertical Alignment... 283
General Considerations .......... 283
General Design Controls ........ 284
Alignment Coordination in Design...................... 285
Other Elements Affecting Geometric Design.............. 286
Drainage. 286
Erosion Control and Landscape Development...... 292
Rest Areas, Information Centers, and Scenic Overlooks ..................... 293
Lighting.. 294
Utilities... 296
General.......................... 296
Urban 297
Rural. 298
Traffic Control Devices ......... 298
Signing and Marking...... 298
Traffic Signals ............... 299
Noise Barriers....................... 300
Fencing... 301
Maintenance of Traffic Through Construction Areas......................... 301
References..... 303

Chapter 4 CROSS SECTION ELEMENTS

General.......... 309
Pavement....... 309
Surface Type......................... 309
Cross Slope........................... 309
Skid Resistance..................... 314
Lane Widths... 315
Shoulders....... 316
General Characteristics.......... 316
Width of Shoulders................ 318
Shoulder Cross Sections......... 319
Shoulder Stability.................. 321
Shoulder Contrast.................. 322
Turnouts . 322
Horizontal Clearance to Obstructions ......................... 322
Curbs............. 323
General Considerations .......... 323xvii
Curb Configurations .............. 324
Curb Placement..................... 326
Drainage Channels and Sideslopes. 327
General Considerations .......... 327
Drainage Channels ................ 327
Sideslopes. 330
Illustrative Outer Cross Sections.... 333
Normal Crown Sections ......... 333
Superelevated Sections .......... 334
Traffic Barriers. 335
General Considerations .......... 335
Longitudinal Barriers............. 337
Roadside Barriers........... 337
Median Barriers............. 338
Bridge Railings ..................... 339
Crash Cushions ..................... 340
Medians ......... 341
Frontage Roads  343
Outer Separations ......................... 346
Noise Control. 348
General Considerations .......... 348
General Design Procedures.... 349
Noise Reduction Designs ....... 350
Roadside Control.......................... 352
General Considerations .......... 352
Driveways  352
Mailboxes. 354
Tunnels.......... 355
General Considerations .......... 355
Types of Tunnels................... 356
General Design Considerations........................... 357
Tunnel Sections..................... 357
Examples of Tunnels ............. 359
Pedestrian Facilities...................... 361
Sidewalks . 361
Grade-Separated Pedestrian Crossings ................ 363
Sidewalk Curb Ramps ........... 365
Bicycle Facilities.......................... 371
Bus Turnouts.. 372
Freeways  372
Arterials.. 372
Park-and-Ride Facilities......... 374
Location ........................ 374
Design........................... 375
On-Street Parking ......................... 377
References..... 380

Chapter 5 LOCAL ROADS AND STREETS

Introduction.... 383
Local Rural Roads ........................ 384
General Design Considerations........................... 384
Design Traffic Volume ... 384
Design Speed................. 384
Sight Distance................ 384
Grades........................... 386
Alignment...................... 386
Cross Slope.................... 387
Superelevation ............... 387
Number of Lanes........... 387
Width of Traveled Way, Shoulder, and Roadway....................... 387
Structures...................... 389
Bridges to Remain in Place......................... 389
Vertical Clearance ......... 389
Right-of-Way Width....... 391
Foreslopes ..................... 391
Horizontal Clearance to Obstructions........... 391
Curbs  392
Intersection Design......... 392
Railroad Highway Grade Crossings............. 392
Traffic Control Devices.. 393
Bicycle Facilities............ 393
Erosion Control.............. 393
Local Urban Streets ...................... 393
General Design Considerations........................... 393
Design Traffic Volume ... 394
Design Speed................. 394
Sight Distance................ 395
Grades........................... 395
Alignment...................... 395
Cross Slope.................... 396
Superelevation ............... 396
Number of Lanes........... 396
Width of Roadway......... 397
Parking Lanes................ 397
Median.......................... 397
Curbs  398
Drainage........................ 398
Cul-De-Sacs and Turnarounds..................... 398
Alleys 400
Sidewalks ...................... 400
Sidewalk Curb Ramps .... 402xix
Driveways ..................... 402
Roadway Widths for Bridges ...................... 403
Horizontal Clearance to Obstructions........... 403
Vertical Clearance ......... 403
Border Area................... 403
Right-of-Way Width....... 404
Provision for Utilities..... 404
Intersection Design......... 404
Railroad-Highway Grade Crossings............. 405
Street and Roadway Lighting ...................... 406
Levels ........................... 407
Traffic Control Devices.. 407
Erosion Control.............. 407
Landscaping................... 407
Bicycle Facilities............ 408
Special-Purpose Roads.................. 408
Introduction.......................... 408
Recreational Roads................ 408
General Considerations... 408
Design Speed................. 409
Design Vehicle............... 410
Sight Distance................ 410
Passing Sight Distance ... 410
Grades........................... 411
Vertical Alignment......... 413
Horizontal Alignment..... 413
Number of Lanes........... 415
Widths of Traveled Way, Shoulder, and Roadway...................... 415
Cross Slope.................... 415
Clear Recovery Area...... 417
Roadside Slopes............. 417
Roadside Barrier............ 417
Signing and Marking...... 418
Structures...................... 418
Resource Recovery Roads ..... 418
Local Service Roads.............. 420
References..... 420

Chapter 6 COLLECTOR ROADS AND STREETS

Introduction.... 423
Rural Collectors 424
General Design Considerations........................... 424
Design Traffic Volumes.. 424
Design Speed................. 424xx
Sight Distance................ 425
Grades........................... 425
Alignment...................... 425
Cross Slope.................... 425
Superelevation ............... 428
Number of Lanes........... 428
Width of Roadway......... 428
Foreslopes ..................... 428
Structures...................... 430
Bridges to Remain in Place......................... 430
Vertical Clearance ......... 431
Horizontal Clearance to Obstructions........... 431
Right-of-Way Width....... 432
Intersection Design......... 432
Railroad-Highway Grade Crossings............. 432
Traffic Control Devices.. 433
Erosion Control.............. 433
Urban Collectors .......................... 433
General Design Considerations........................... 433
Design Traffic Volumes.. 434
Design Speed................. 434
Sight Distance................ 435
Grades........................... 435
Alignment...................... 435
Cross Slope.................... 435
Superelevation ............... 435
Number of Lanes........... 437
Width of Roadway......... 437
Parking Lanes................ 437
Medians......................... 438
Curbs  439
Drainage........................ 439
Sidewalks ...................... 440
Driveways ..................... 440
Roadway Widths for Bridges ...................... 440
Vertical Clearance ......... 440
Horizontal Clearance to Obstructions........... 441
Right-of-Way Width....... 441
Provision for Utilities..... 441
Border Area................... 442
Intersection Design......... 442
Railroad-Highway Grade Crossings............. 443
Street and Roadway Lighting ...................... 443
Traffic Control Devices.. 443
Erosion Control.............. 444
Landscaping................... 444xxi
References..... 444

Chapter 7 RURAL AND URBAN ARTERIALS

Introduction.... 447
Rural Arterials 447
General Characteristics.......... 447
General Design Considerations........................... 448
Design Speed................. 448
Design Traffic Volume ... 448
Levels of Service ........... 448
Sight Distance................ 449
Alignment...................... 449
Grades........................... 450
Number of Lanes........... 450
Superelevation ............... 450
Cross Slope.................... 450
Vertical Clearances ........ 451
Structures...................... 451
Traffic Control Devices.. 451
Erosion Control.............. 451
Widths........................... 452
Horizontal Clearance to Obstructions........... 452
Cross Section and Right-of-Way................. 453
Provision for Passing...... 453
Ultimate Development of Four-Lane Divided Arterials............... 454
Multilane Undivided Arterials  457
Divided Arterials................... 458
General Features............ 458
Lane Widths .................. 459
Cross Slope.................... 459
Shoulders ...................... 459
Median Barrier Clearance........................... 460
Medians......................... 460
Alignment and Profile .... 461
Climbing Lanes on Multilane Arterials ........ 462
Superelevated Cross Sections...................... 463
Cross Section and Right-of-Way Widths...... 466
Sections With Widely Separated Roadways. 469
Intersections................... 470
Access Management....... 471
Bikeways and Pedestrian Facilities.............. 471
Bus Turnouts ................. 472
Railroad-Highway Crossings....................... 472
Rest Areas..................... 472xxii
Urban Arterials. 473
General Characteristics.......... 473
General Design Considerations........................... 474
Design Speed................. 474
Design Traffic Volume ... 474
Levels of Service ........... 474
Sight Distance................ 475
Alignment...................... 475
Grades........................... 475
Superelevation ............... 475
Cross Slope.................... 476
Vertical Clearances ........ 476
Lane Widths .................. 476
Curbs and Shoulders....... 477
Number of Lanes........... 477
Width of Roadway......... 478
Medians......................... 478
Drainage........................ 482
Parking Lanes................ 482
Borders and Sidewalks ... 483
Railroad-Highway Crossings....................... 484
Roadway Width for Bridges........................ 485
Bridges to Remain in Place......................... 485
Horizontal Clearance to Obstructions........... 485
Right-of-Way Width....... 486
Traffic Barriers.............. 486
Access Management.............. 486
General Features............ 486
Access Control by Statute ........................... 487
Access Control by Zoning........................... 487
Access Control Through Driveway Regulations ......................... 487
Access Control Through Geometric Design.. 488
Pedestrian Facilities............... 488
Provision for Utilities ............ 490
Intersection Design................ 490
Operational Control and Regulations .................. 490
Traffic Control Devices.. 490
Regulatory Measures...... 492
Operational and Control Measures for Right-Turn Maneuvers..... 492
Operational and Control Measures for Left-Turn Maneuvers ...... 492
Regulation of Curb Parking......................... 495
Directional Lane Usage .. 495
Frontage Roads and Outer Separations................ 498
Grade Separations and Interchanges ................... 498
Erosion Control..................... 500
Lighting.. 500xxiii
Bikeways 500
Public Transit Facilities ......... 500
Location of Bus Stops..... 501
Bus Turnouts ................. 504
Reserved Bus Lanes....... 504
Traffic Control Measures 505
References..... 506

Chapter 8 FREEWAYS

Introduction.... 507
General Design Considerations...... 507
Design Speed........................ 507
Design Traffic Volumes......... 508
Levels of Service................... 508
Pavement and Shoulders........ 508
Curbs...... 509
Superelevation....................... 509
Grades.... 509
Structures . 510
Vertical Clearance................. 510
Horizontal Clearance to Obstructions.................. 511
Ramps and Terminals ............ 512
Outer Separations, Borders, and Frontage Roads . 512
Rural Freeways  512
Alignment and Profile............ 513
Medians.. 513
Sideslopes. 516
Frontage Roads ..................... 516
Urban Freeways ........................... 517
General Design Characteristics........................... 517
Medians.. 517
Depressed Freeways.............. 517
General Characteristics... 517
Slopes and Walls............ 518
Typical Cross Section..... 519
Restricted Cross Section . 521
Walled Cross Section...... 521
Examples of Depressed Freeways ............... 522
Elevated Freeways ................ 524
General Characteristics... 524
Medians......................... 525
Ramps and Terminals ..... 525
Frontage Roads.............. 526
Clearance to Building Line ......................... 526xxiv
Typical Cross Section..... 526
Viaduct Freeways Without Ramps............... 527
Two-Way Viaduct Freeways With Ramps ... 528
Freeways on Earth Embankment................. 529
Examples of Elevated Freeways.................. 530
Ground-Level Freeways ........ 531
General Characteristics... 531
Typical Cross Section..... 532
Restricted Cross Section . 533
Example of a Ground-Level Freeway.......... 534
Combination-Type Freeways . 534
General Characteristics... 534
Profile Control............... 535
Cross-Section Control..... 537
Examples of Combination-Type Freeways... 537
Special Freeway Designs ....... 541
Reverse-Flow Roadways  541
Dual-Divided Freeways.. 544
Freeways With Collector-Distributor Roads. 547
Accommodation of Transit and  High-Occupancy Vehicle Facilities... 547
General Considerations... 547
Buses 549
Rail Transit.................... 554
References..... 558

Chapter 9 INTERSECTIONS

Introduction.... 559
General Design Considerations and Objectives........... 559
Types and Examples of Intersections.......................... 562
General Considerations .......... 562
Three-Leg Intersections ......... 563
Basic Types of Intersections........................ 563
Channelized Three-Leg Intersections........... 568
Four-Leg Intersections........... 569
Basic Types................... 569
Channelized Four-Leg Intersections ............ 570
Multileg Intersections ............ 575
Modern Roundabouts............. 578
Capacity Analysis ......................... 583
Alignment and Profile ................... 583
General Considerations .......... 583
Alignment. 584
Profile..... 586
Types of Turning Roadways.......... 587xxv
General... 587
Minimum Edge-of-Traveled-Way Designs.......... 587
Design for Specific Conditions (Right-Angle Turns).......................... 596
Passenger Vehicles......... 597
Single-Unit Trucks and City Transit Buses .. 613
Semitrailer Combination Trucks.................. 614
Oblique-Angle Turns...... 614
Effect of Curb Radii on Turning Paths......... 615
Effect of Curb Radii on Pedestrians............. 618
Corner Radii Into Local Urban Streets......... 625
Islands ........... 625
General Characteristics.......... 625
Channelizing Islands.............. 627
Divisional Islands.................. 629
Refuge Islands ...................... 630
Island Size and Designation.... 631
Island Delineation and Approach Treatment........ 632
Turning Roadways With Corner Islands ..................... 638
Right-Angle Turns With Corner Islands....... 638
Oblique-Angle Turns With Corner Islands .......... 641
Free-Flow Turning Roadways at Intersections ............ 643
Superelevation for Turning Roadways at Intersections  643
General Design Guidelines..... 643
Superelevation Runoff ........... 646
Development of Superelevation at Turning Roadway Terminals ......... 646
General Procedure ......... 647
Turn-Lane Cross-Slope Rollover................. 652
Superelevation Transition and Gradeline Control........................ 652
Traffic Control Devices................. 653
Intersection Sight Distance............ 654
General Considerations .......... 654
Sight Triangles...................... 655
Approach Sight Triangles ........................... 655
Departure Sight Triangles........................... 657
Identification of Sight Obstructions Within Sight Triangles......... 657
Intersection Control............... 658
Case A—Intersections With No Control....... 658
Case B—Intersections With Stop Control on the Minor Road...... 660
Case B1—Left Turn From the Minor Road.. 660
Case B2—Right Turn from the Minor Road. 667
Case B3—Crossing Maneuver from the Minor Road.................. 667
Case C—Intersections With Yield Control on the Minor Road.... 670
Case C1—Crossing Maneuver From the Minor Road................. 670
Case C2—Left- and Right-Turn Maneuvers. 675
Case D—Intersections With Traffic Signal Control..................... 675
Case E—Intersections With All-Way Stop Control..................... 678xxvi
Case F—Left Turns From the Major Road... 678
Effect of Skew...................... 681
Stopping Sight Distance at Intersections for Turning Roadways................. 682
General Considerations .......... 682
Vertical Control..................... 682
Horizontal Control................. 683
Design to Discourage Wrong-Way Entry.................... 683
General Intersection Types............ 686
General Design Considerations........................... 686
Channelization 690
Speed-Change Lanes at Intersections ......................... 692
Median Openings.......................... 693
General Design Considerations........................... 693
Control Radii for Minimum Turning Paths.......... 694
Shape of Median End............. 701
Minimum Length of Median Opening................. 701
Median Openings Based on Control Radii for Design Vehicles........... 702
Passenger Vehicles......... 702
Single-Unit Trucks or Buses....................... 703
Semitrailer Combinations 704
Effect of Skew...................... 704
Above-Minimum Designs for Direct Left Turns.. 706
Indirect Left Turns and U-turns ..... 709
General Design Considerations........................... 709
Indirect Left Turn or Indirect U-Turn—Using Local Streets............... 711
Indirect Left Turn or Indirect U-Turn—Wide Medians....................... 712
Location and Design of U-Turn Median Openings. 713
Flush or Traversable Medians........ 716
Auxiliary Lanes 717
General Design Considerations........................... 717
Deceleration Length............... 718
Storage Length...................... 718
Taper...... 719
Median Left-Turn Lanes........ 720
Median End Treatment .......... 726
Offset Left-Turn Lanes.......... 727
Simultaneous Left Turns ............... 727
Intersection Design Elements with  Frontage Roads.... 729
Bicycles at Intersections................ 732
WheelChair Ramps at Intersections 732
Lighting at Intersections................ 733
Driveways...... 733
Railroad-Highway Grade Crossings ........................... 735
Horizontal Alignment ............ 735
Vertical Alignment................ 735
General... 736xxvii
References..... 743

Chapter 10 GRADE SEPARATIONS AND INTERCHANGES

Introduction and General Types of Interchanges......... 747
Warrants for Interchanges and Grade Separations ....... 749
Adaptability of Highway Grade Separations and Interchanges................... 751
Traffic and Operation............. 751
Site Conditions...................... 752
Type of Highway and Intersecting Facility.......... 752
Access Separations and Control on the Crossroad at Interchanges.............. 753
Safety..... 755
Stage Development................ 755
Economic Factors.................. 755
Initial Costs ................... 755
Maintenance Costs......... 755
Vehicular Operating Costs.......................... 756
Grade Separation Structures .......... 756
Introduction.......................... 756
Types of Separation Structures........................... 756
Overpass Versus Underpass Roadways............... 762
General Design Considerations ................... 762
Structure Widths ............ 764
Underpass Roadways ............ 765
Lateral Clearances ......... 765
Vertical Clearance ......... 767
Overpass Roadways .............. 768
Bridge Railings .............. 768
Lateral Clearances ......... 770
Medians......................... 770
Longitudinal Distance to Attain Grade Separation 771
Grade Separations Without Ramps ..................... 773
Interchanges... 774
General Considerations .......... 774
Three-Leg Designs ................ 775
Four-Leg Designs.................. 780
Ramps in One Quadrant . 780
Diamond Interchanges.... 782
Single-Point Urban Interchanges................. 787
Cloverleafs.................... 792
Directional and Semidirectional Interchanges. 798
Other Interchange Configurations ....................... 803
Offset Interchanges........ 803
Combination Interchanges.......................... 803
General Design Considerations........................... 806xxviii
Determination of Interchange Configuration 806
Approaches to the Structure........................ 809
Interchange Spacing ....... 811
Uniformity of Interchange Patterns ............. 811
Route Continuity............ 811
Overlapping Routes........ 813
Signing and Marking...... 813
Basic Number of Lanes.. 814
Coordination of Lane Balance and Basic Number of Lanes......... 815
Auxiliary Lanes ............. 818
Lane Reductions............. 822
Weaving Sections........... 823
Collector-Distributor Roads ........................ 823
Two-Exit Versus Single-Exit Interchange Design....................... 824
Wrong-Way Entrances... 825
Ramps .... 827
Types and Examples....... 827
General Ramp Design Considerations.......... 829
Ramp Traveled-Way Widths....................... 842
Ramp Terminals............. 844
Single-Lane Free-Flow Terminals, Entrances. 849
Single-Lane Free-Flow Terminals, Exits...... 853
Other Interchange Design Features..................... 867
Testing for Ease of Operation...................... 867
Pedestrians .................... 868
Ramp Metering.............. 869
Grading and Landscape Development.......... 869
Models .......................... 871
References 871
LIST OF EXHIBITS
1- Hierarchy of Movement.....2
1-2 Channelization of Trips......4
1-3 Schematic Illustration of a Functionally Classified Rural  Highway Network...............5
1-4 Schematic Illustration of a Portion of a Suburban Street Network...6
1-5 Relationship of Functionally Classified Systems in Serving Traffic Mobility and
Land Access......................7
1-6 Typical Distribution of Rural Functional Systems ........................ 10
1-7 Typical Distribution of Urban Functional Systems ....................... 12
2-1 Design Vehicle Dimensions.......................... 16
2-2 Minimum Turning Radii of Design Vehicles . 19
2-3 Minimum Turning Path for Passenger Car (P) Design Vehic le...... 21
2-4 Minimum Turning Path for Single-Unit (SU) Truck Design Vehicle ......................... 22
2-5 Minimum Turning Path for Intercity Bus (BUS-12 [BUS-40]) Design Vehicle .......... 23
2-6 Minimum Turning Path for Intercity Bus (BUS-14 [BUS-45]) Design Vehicle .......... 24
2-7 Minimum Turning Path for City Transit Bus (CITY-BUS) Design Vehicle................ 25
2-8 Minimum Turning Path for Conventional School Bus (S-BUS-11 [S-BUS-36])
Design Vehicle ................ 26
2-9 Minimum Turning Path for Large School Bus (S-BUS-12 [S-BUS-40])
Design Vehicle ................ 27
2-10 Minimum Turning Path for Articulated Bus (A-BUS) Design Vehicle....................... 28
2-11 Turning Characteristics of a Typical Tractor-Semitrailer Combination Truck............. 29
2-12 Lengths of Commonly Used Truck Tractors.. 30
2-13 Minimum Turning Path for Intermediate Semitrailer (WB-12 [WB-40])
Design Vehicle ................ 31
2-14 Minimum Turning Path for Intermediate Semitrailer (WB-15 [WB-50])
Design Vehicle ................ 32
2-15 Minimum Turning Path for Interstate Semitrailer (WB-19 [WB-62])
Design Vehicle ................ 33
2-16 Minimum Turning Path for Interstate Semitrailer (WB-20 [WB-65 and WB-67])
Design Vehicle ................ 34
2-17 Minimum Turning Path for Double-Trailer Combination (WB-20D [WB-67D])
Design Vehicle ................ 35
2-18 Minimum Turning Path for Triple-Trailer Combination (WB-30T [WB-100T])
Design Vehicle ................ 36
2-19 Minimum Turning Path for Turnpike-Double Combination (WB-33D [WB-109D])
Design Vehicle ................ 37
2-20 Minimum Turning Path for Motor Home (MH) Design Vehicle .... 38
2-21 Minimum Turning Path for Passenger Car and Camper Trailer (P/T)
Design Vehicle ................ 39
2-22 Minimum Turning Path for Passenger Car and Boat Trailer (P/B) Design Vehicle ..... 40
2-23 Minimum Turning Path for Motor Home and Boat Trailer (MH/B) Design Vehicle ... 41
2-24 Acceleration of Passenger Cars, Level Conditions........................ 44xxx
2-25 Deceleration Distances for Passenger Vehicles Approaching Intersections................. 45
2-26 Median Driver Reaction Time to Expected and Unexpected Information................... 51
2-27 85th-Percentile Driver Reaction Time to Expected and Unexpected Information........ 52
2-28 Relation Between Peak-Hour and Average Daily Traffic Volumes on
Rural Arterials................. 60
2-29 Corresponding Design Speeds in Metric and US Customary Units 70
2-30 Generalized Speed-Volume-Density Relationships (15)................ 73
2-31 General Definitions of Levels of Service....... 84
2-32 Guidelines for Selection of Design Levels of Service................... 85
2-33 Weaving Sections ............ 87
2-34 Simple and Multiple Weaving Sections ......... 87
2-35 Estimated Crash Rates by Type of Median—Urban and Suburban Areas (18)............ 93
2-36 Estimated Crash Rates by Type of Median—Rural Areas (18)...... 94
2-37 Estimated Crash Rates by Unsignalized and Signalized Access Density—
Urban and Suburban Areas (18).................... 95
3-1 Stopping Sight Distance. 112
3-2 Stopping Sight Distance on Grades............. 115
3-3 Decision Sight Distance. 116
3-4 Elements of Passing Sight Distance for Two-Lane Highways ..... 119
3-5 Elements of Safe Passing Sight Distance for Design of Two-Lane Highways........... 120
3-6 Total Passing Sight Distance and Its Components—Two-Lane Highways ............... 123
3-7 Passing Sight Distance for Design of Two-Lane Highways......... 124
3-8 Scaling and Recording Sight Distances on Plans........................ 129
3-9 Geometry for Ball-Bank Indicator............... 134
3-10 Side Friction Factors...... 136
3-11 Comparison of Side Friction Factors Assumed for Design of Different Types of
Facilities ....................... 137
3-12 Methods of Distributing Superelevation and Side Friction .......... 139
3-13 Side Friction Factors for Rural Highways and High-Speed Urban Streets................ 144
3-14 Minimum Radius for Design of Rural Highways, Urban Freeways,
and High-Speed Urban Streets Using Limiting Values of e and f  145
3-15 Method 5 Procedure for Development of the Finalized e Distribution...................... 146
3-16 Design Superelevation Rates for Maximum Superelevation Rate of 4 Percent ......... 147
3-17 Design Superelevation Rates for Maximum Superelevation Rate of 6 Percent ......... 148
3-18 Design Superelevation Rates for Maximum Superelevation Rate of 8 Percent ......... 149
3-19 Design Superelevation Rates for Maximum Superelevation Rate of 10 Percent........ 150
3-20 Design Superelevation Rates for Maximum Superelevation Rate of 12 Percent........ 151
3-21 Values for Design Elements Related to Design Speed and Horizontal Curvature...... 156
3-22 Values for Design Elements Related to Design Speed and Horizontal Curvature...... 158
3-23 Values for Design Elements Related to Design Speed and Horizontal Curvature...... 160
3-24 Values for Design Elements Related to Design Speed and Horizontal Curvature...... 162
3-25 Values for Design Elements Related to Design Speed and Horizontal Curvature...... 164
3-26 Minimum Curve Radius for Section with Normal Cross Slopes (emax = 10%)........ 168
3-27 Maximum Relative Gradients..................... 170
3-28 Adjustment Factor for Number of Lanes Rotated....................... 172
3-29 Minimum Superelevation Runoff and Tangent Runout Lengths .. 174xxxi
3-30 Runoff Locations that Minimize the Vehicle’s Lateral Motion.... 175
3-31 Limiting Superelevation Rates.................... 176
3-32 Transition Spirals (23).... 178
3-33 Maximum Radius for Use of a Spiral Curve Transition............... 179
3-34 Desirable Length of Spiral Curve Transition 181
3-35 Superelevation Rates Associated With Large Relative Gradients. 182
3-36 Tangent Runout Length for Spiral Curve Transition Design........ 183
3-37 Diagrammatic Profiles Showing Methods of Attaining Superelevation for a
Curve to the Right.......... 185
3-38 Lengths of Circular Arcs for Different Compound Curve Radii... 192
3-39 Side Friction Factors for Low-Speed Urban Streets.................... 194
3-40 Relationship of Radius Superelevation, Cross Slope Rate, and Design Speed for
Low-Speed Urban Street Design................. 196
3-41 Minimum Radii and Minimum Lengths of Superelevation Runoff for Limiting
Values of e and f (Low-Speed Urban Streets) 197
3-42 Relation Between Speed and Side Friction Factor on Curves at Intersections ........... 200
3-43 Minimum Radii for Intersection Curves ...... 201
3-44 Minimum Radii for Curves at Intersections . 202
3-45 Minimum Lengths of Spiral for Intersection Curves................... 204
3-46 Length of Circular Arc for a Compound Intersection Curve When Followed by
a Curve of One-Half Radius or Preceded by a Curve of Double Radius ................... 206
3-47 Track Width for Widening of Traveled Way on Curves.............. 208
3-48 Front Overhang for Widening of Traveled Way on Curves......... 210
3-49 Extra Width Allowance for Difficulty of Driving on Traveled Way on Curves......... 211
3-50 Widening Components on Open Highway Curves (Two-Lane Highways,
One-Way or Two-Way) . 213
3-51 Calculated and Design Values for Traveled Way Widening on Open Highway
Curves (Two-Lane Highways, One-Way or Two-Way).............. 215
3-52 Adjustments for Traveled Way Widening Values on Open Highway Curves
(Two-Lane Highways, One-Way or Two-Way) ......................... 217
3-53 Derivation of Turning Roadway Widths on Curves at Intersections......................... 219
3-54 Derived Pavement Widths for Turning Roadways for Different Design Vehicles..... 221
3-55 Design Widths of Pavements for Turning Roadways.................. 224
3-56 Range of Usable Shoulder Widths or Equivalent Lateral Clearances Outside of
Turning Roadways, Not on Structure .......... 228
3-57 Design Controls for Stopping Sight Distance on Horizontal Curves ........................ 229
3-58 Diagram Illustrating Components for Determining Horizontal Sight Distance.......... 231
3-59 Speed-Distance Curves for a Typical Heavy Truck of 120 kg/kW [200 lb/hp] for
Deceleration on Upgrades .......................... 237
3-60 Speed-Distance Curves for Acceleration of a Typical Heavy Truck of 120 kg/kW
[200 lb/hp] on Upgrades and Downgrades... 238
3-61 Speed-Distance Curves for a Typical Recreational Vehicle on the Selected
Upgrades (40) ............... 240
3-62 Crash Involvement Rate of Trucks for Which Running Speeds Are Reduced
Below Average Running Speed of All Traffic (41)..................... 241xxxii
3-63 Critical Lengths of Grade for Design, Assumed Typical Heavy Truck of
120 kg/kW [200 lb/hp], Entering Speed = 110 km/h [70 mph] .... 245
3-64 Critical Lengths of Grade Using an Approach Speed of 90 km/h [55 mph] for
Typical Recreational Vehicle (40)............... 246
3-65 Climbing Lanes on Two-Lane Highways .... 248
3-66 Climbing Lane on Freeways and Multilane Highways................ 254
3-67 Passing Lanes Section on Two-Lane Roads. 256
3-68 Recommended Lengths of Turnouts Including Taper ................. 258
3-69 Forces Acting on a Vehicle in Motion......... 260
3-70 Rolling Resistance of Roadway Surfacing Materials .................. 260
3-71 Basic Types of Emergency Escape Ramps .. 263
3-72 Typical Emergency Escape Ramp............... 267
3-73 Types of Vertical Curves 269
3-74 Parameters Considered in Determining the Length of a Crest Vertical Curve to
Provide Sight Distance... 271
3-75 Design Controls for Crest Vertical Curves—Open Road Conditions........................ 273
3-76 Design Controls for Stopping Sight Distance and for Crest and Sag
Vertical Curves ............. 274
3-77 Design Controls for Crest Vertical Curves Based on Passing Sight Distance............ 276
3-78 Design Controls for Sag Vertical Curves—Open Road Conditions.......................... 278
3-79 Design Controls for Sag Vertical Curves..... 280
3-80 Sight Distance at Undercrossings................ 281
3-81 Alignment and Profile Relationships in Roadway Design (48) .... 287
4-1 Typical Cross Section, Normal Crown........ 310
4-2 Typical Cross Section, Superelevated.......... 311
4-3 Roadway Sections for Divided Highway (Basic Cross Slope Arrangements)........... 312
4-4 Normal Traveled-Way Cross Slope............. 314
4-5 Graded and Usable Shoulders..................... 317
4-6 Typical Highway Curbs . 325
4-7 Designation of Roadside Regions................ 330
4-8 Typical Frontage Road Arrangements......... 344
4-9 Frontage Roads, Irregular Pattern............... 345
4-10 One-way Frontage Roads, Entrance and Exit Ramps.................. 346
4-11 Two-way Frontage Roads, Entrance and Exit Ramps ................. 346
4-12 Frontage Road in Business Area With Narrow Outer Separation. 347
4-13 Typical Outer Separations .......................... 348
4-14 Noise-Abatement Criteria for Various Land Uses...................... 350
4-15 Effects of Depressing the Highway............. 351
4-16 Effects of Elevating the Highway................ 352
4-17 Typical Two-lane Tunnel Sections.............. 358
4-18 Diagrammatic Tunnel Sections ................... 360
4-19 Entrance to a Freeway Tunnel..................... 360
4-20 Interior of a 3-lane One-way Tunnel............ 361
4-21 Typical Pedestrian Overpasses on Major Highways ................... 366
4-22 Mid-block Sidewalk Curb Ramp Details...... 368xxxiii
4-23 Sidewalk Curb Ramp at Middle of Radius—Discouraged Where Pedestrian
and/or Vehicular Volumes are Moderate to High........................ 369
4-24 Sidewalk Curb Ramp at End of Curb Radius . 370
4-25 Sidewalk Curb Ramp at Midblock............... 370
4-26 Median and Island Openings....................... 371
4-27 Bus Turnouts................. 373
4-28 Midblock Bus Turnout... 374
4-29 Sawtooth Bus Loading Area....................... 376
4-30 Typical Park-and-Ride Facility................... 378
4-31 Parking Lane Transition at Intersection ....... 379
5-1 Minimum Design Speeds for Local Rural Roads........................ 385
5-2 Design Controls for Stopping Sight Distance and for Crest and Sag Vertical
Curves.......................... 385
5-3 Design Controls for Crest Vertical Curves Based on Passing Sight Distance............ 386
5-4 Maximum Grades for Local Rural Roads .... 386
5-5 Minimum Width of Traveled Way and Shoulders ...................... 388
5-6 Minimum Clear Roadway Widths and Design Loadings for New and
Reconstructed Bridges ... 390
5-7 Minimum Structural Capacities and Minimum Roadway Widths for Bridges to
Remain in Place ............ 390
5-8 Types of Cul-de-Sacs and Dead-End Streets 399
5-9 Alley Turnarounds......... 401
5-10 Actual Curb Radius and Effective Radius for Right-Turn Movements at
Intersections .................. 405
5-11 Minimum Illumination Levels .................... 406
5-12 Potential Road Network. 409
5-13 Design Controls for Stopping Sight Distance and for Crest and Sag Vertical
Curves—Recreational Roads ...................... 411
5-14 Design Controls for Passing Sight Distance for Crest Vertical Curves—
Recreational Roads ........ 412
5-15 Maximum Grades for Recreational Roads ... 413
5-16 Minimum-Radius Horizontal Curve for Gravel Surface.............. 414
5-17 Turnout Design.............. 416
5-18 Widths of Traveled Way and Shoulders—Recreational Roads .... 416
5-19 Design Speeds for Resource Recovery and Local Service Roads  419
6-1 Minimum Design Speeds for Rural Collectors........................... 426
6-2 Design Controls for Stopping Sight Distance and for Crest and Sag Vertical
Curves.......................... 426
6-3 Design Controls for Crest Vertical Curves  Based on Passing Sight Distance........... 427
6-4 Maximum Grades for Rural Collectors........ 427
6-5 Minimum Width of Traveled Way and Shoulders ...................... 429
6-6 Minimum Roadway Widths and Design Loadings for  New and Reconstructed
Bridges ......................... 430
6-7 Structural Capacities and Minimum Roadway Widths for Bridges to Remain in
Place  431
6-8 Maximum Grades for Urban Collectors....... 436xxxiv
7-1 Minimum Sight Distances for Arterials ....... 449
7-2 Maximum Grades for Rural Arterials .......... 450
7-3 Minimum Width of Traveled Way and Usable Shoulder for Rural Arterials............. 452
7-4 Climbing Lane on Two-Lane Rural Arterial. 454
7-5 Two-Lane Arterial Cross Section With Ultimate Development to a Four-Lane
Arterial......................... 457
7-6 Methods of Attaining Superelevation on Divided Arterials ......... 465
7-7 Typical Medians on Divided Arterials......... 466
7-8 Cross Sectional Arrangements on Divided Arterials ................... 468
7-9 Cross Sectional Arrangements on Divided Arterials ................... 469
7-10 Maximum Grades for Urban Arterials ......... 476
7-11 Continuous Two-Way Left-Turn Lane ........ 480
7-12 Parking Turnouts in Downtown District...... 483
7-13 Arterial Street in Residential Area .............. 484
7-14 Divided Arterial Street With Parking Lanes. 485
7-15 Urban Arterial With Dual Left-Turn Lanes.. 494
7-16 Divided Arterial Street With Two-Way Frontage Road.............. 499
7-17 Bus Stops at Special Locations Adjacent to Certain Arterials...... 503
7-18 Exclusive Bus Lane ....... 505
8-1 Maximum Grades for Rural and Urban Freeways ...................... 510
8-2 Typical Ground-Level Rural Freeway......... 514
8-3 Typical Rural Medians... 515
8-4 Typical Cross Section for Depressed Freeways.......................... 520
8-5 Restricted Cross Sections for Depressed Freeways..................... 520
8-6 Cross Sections with Retaining Walls on Depressed Freeways Without Ramps ......... 522
8-7 Depressed Freeway........ 523
8-8 Depressed Freeway........ 524
8-9 Typical Cross Sections for Elevated Freeways on Structures Without Ramps........... 528
8-10 Typical and Restricted Cross Sections for Elevated Freeways on Structure With
Frontage Roads ............. 529
8-11 Typical and Restricted Cross Sections for Elevated Freeways on Embankment........ 530
8-12 Viaduct Freeway........... 531
8-13 Two-Level Viaduct Freeway...................... 532
8-14 Typical Cross Sections for Ground-Level Freeways................... 533
8-15 Restricted Cross Sections for Ground-Level Freeways ............... 534
8-16 Profile Control—Rolling Terrain Combination-Type Freeway.... 535
8-17 Profile Control—Flat Terrain Combination-Type Freeway......... 536
8-18 Cross-Section Control—Combination-Type Freeway................. 538
8-19 Combination-Type Freeway....................... 539
8-20 Four-Level Cantilevered Freeway............... 540
8-21 Typical Cross Sections for Reverse-Flow Operation................... 541
8-22 Typical Reverse Roadway Terminals .......... 543
8-23 Reverse-Flow Freeway.. 544
8-24 Typical Dual-Divided Freeway................... 546
8-25 Dual-Divided Freeway With a 4-3-3-4 Roadway Arrangement... 546
8-26 Bus Roadway Located Between a Freeway and a Parallel Frontage Road................ 548xxxv
8-27 Bus Stops at Freeway Level....................... 551
8-28 Bus Stops at Freeway-Level Diamond Interchange .................... 552
8-29 Freeway-Level Bus Stop at Cloverleaf Interchange.................... 552
8-30 Bus Stops at Street Level on Diamond Interchange .................... 553
8-31 Joint Freeway-Transit Right-of-Way........... 555
8-32 Typical Sections With Rail Transit in Freeway Median.............. 556
8-33 Example of Transit Station Layout.............. 557
8-34 Depressed Freeway With Rail Rapid Transit in the Median........ 558
9-1 Physical and Functional Intersection Area... 561
9-2 Elements of the Functional Area of an Intersection..................... 561
9-3 Channelized High-Type “T” Intersections ... 563
9-4 Three-Leg Rural Intersection, Channelized “T” ......................... 563
9-5 “T” Intersections............ 564
9-6 Channelized “T” Intersections .................... 565
9-7 “T” Intersections............ 566
9-8 Channelized “T” Intersections .................... 567
9-9 Unchannelized Four-Leg Intersections, Plain and Flared............ 570
9-10 Channelized Four-Leg Intersections............ 571
9-11 Channelized Four-Leg Intersections............ 572
9-12 Four-Leg Intersections (Channelized High-type)........................ 574
9-13 Four-Leg Intersections (Channelized High-type)........................ 576
9-14 Realigning Multi-Leg Intersections ............. 577
9-15 Geometric Elements of a Single-Lane Modern Roundabout........ 579
9-16 Typical Modern Roundabout ...................... 580
9-17 Roundabout with Entry Flaring in Two Quadrants..................... 582
9-18 Realignment Variations at Intersections....... 584
9-19 Edge-of-Traveled-Way Designs for Turns at Intersections.......... 588
9-20 Edge of Traveled Way for Turns at Intersections........................ 592
9-21 Minimum Traveled Way (Passenger Vehicles) .......................... 598
9-22 Minimum Traveled Way Designs (Single-Unit Trucks and City Transit Buses) ....... 600
9-23 Minimum Edge-of-Traveled-Way Designs (WB-12 [WB-40] Design
Vehicle Path) ................ 602
9-24 Minimum Edge-of-Traveled-Way Designs (WB-15 [WB-50]) Design
Vehicle Path) ................ 604
9-25 Minimum Edge-of-Traveled-Way Designs (WB-15 [WB-50]) Design
Vehicle Path) ................ 605
9-26 Minimum Edge-of-Traveled-Way Designs (WB-19 [WB-62]) Design
Vehicle Path) ................ 607
9-27 Minimum Edge-of-Traveled-Way Designs (WB-30T [WB-100T] Design
Vehicle Path) ................ 609
9-28 Minimum Edge-of-Traveled-Way Designs (WB-33D [WB-109D] Design
Vehicle Path) ................ 611
9-29 Effect of Curbed Radii on Right Turning Paths of Various Design Vehicles ............ 616
9-30 Effect of Curbed Radii on Right Turning Paths of Various Design Vehicles ............ 617
9-31 Cross Street Width Occupied by Turning Vehicle for Various Angles of
Intersection and Curb Radii........................ 619xxxvi
9-32 Effect of Curbed Radii and Parking on Right Turning Paths ....... 621
9-33 Variations in Length of Crosswalk With Different Curb Radii and Width of
Borders......................... 624
9-34 Corner Setbacks with Different Curb Radii and Width of Borders........................... 624
9-35 General Types and Shapes of Islands and Medians..................... 628
9-36 Alignment for Addition of Divisional Islands at Intersections ..... 630
9-37 Details of Corner Island Designs for Turning Roadways (Urban Location) .............. 634
9-38 Details of Corner Island Designs for Turning Roadways (Rural Cross Section on
Approach)..................... 635
9-39 Nose Ramping at Approach End of Median or Corner Island...... 636
9-40 Details of Divisional Island Design............. 637
9-41 Minimum Turning Roadway Designs With Corner Islands at Urban Locations ........ 639
9-42 Typical Designs for Turning Roadways....... 642
9-43 Use of Simple and Compound Curves at Free Flow Turning Roadways .................. 644
9-44 Effective Maximum Relative Gradients....... 647
9-45 Development of Superelevation at Turning Roadway Terminals . 648
9-46 Development of Superelevation at Turning Roadway Terminals . 649
9-47 Development of Superelevation at Turning Roadway Terminals . 650
9-48 Development of Superelevation at Turning Roadway Terminals . 651
9-49 Maximum Algebraic Difference in Cross Slope at Turning Roadway Terminals ...... 652
9-50 Intersection Sight Triangles........................ 656
9-51 Length of Sight Triangle Leg—Case A—No Traffic Control...... 659
9-52 Length of Sight Triangle Leg—Case A—No Traffic Control...... 661
9-53 Adjustment Factors for Sight Distance Based on Approach Grade .......................... 662
9-54 Time Gap for Case B1—Left Turn from Stop 664
9-55 Design Intersection Sight Distance—Case B1—Left Turn From Stop ..................... 665
9-56 Intersection Sight Distance—Case B1—Left Turn from Stop ..... 666
9-57 Time Gap for Case B2—Right Turn from Stop and Case B3—Crossing Maneuver.. 668
9-58 Design Intersection Sight Distance—Case B2—Right Turn from Stop and
Case B3—Crossing Maneuver.................... 668
9-59 Intersection Sight Distance—Case B2—Right Turn from Stop and Case B3—
Crossing Maneuver........ 669
9-60 Case C1—Crossing Maneuvers From Yield-Controlled Approaches—Length of
Minor Road Leg and Travel Times ............. 672
9-61 Length of Sight Triangle Leg Along Major Road—Case C1—Crossing
Maneuver at Yield Controlled Intersections . 673
9-62 Length of Sight Triangle Leg Along Major Road for Passenger Cars—
Case C1—Crossing Maneuver.................... 674
9-63 Time Gap for Case C2—Left or Right Turn. 676
9-64 Design Intersection Sight Distance—Case C2—Left or Right Turn at
Yield Controlled Intersections .................... 676
9-65 Intersection Sight Distance—Case C2—Yield Controlled Left or Right Turn........... 677
9-66 Time Gap for Case F—Left Turns From the Major Road............ 678
9-67 Intersection Sight Distance—Case F—Left Turn From Major Road........................ 679
9-68 Intersection Sight Distance—Case F—Left Turn From Major Road........................ 680
9-69 Sight Triangles at Skewed Intersections ...... 681xxxvii
9-70 Stopping Sight Distance for Turning Roadways......................... 682
9-71 Two-Lane Crossroad Designs to Discourage Wrong-Way Entry. 684
9-72 Divided Crossroad Designs to Discourage Wrong-Way Entry..... 685
9-73 General Types of Intersections.................... 687
9-74 General Types of Intersections.................... 688
9-75 Guide for Left-Turn Lanes on Two-Lane Highways (6).............. 689
9-76 Control Radii at Intersections for 90-Degree Left Turns ............. 695
9-77 Minimum Design of Median Openings (P Design Vehicle, Control Radius of
12 m [40 ft]).................. 697
9-78 Minimum Design of Median Openings (P Design Vehicle, Control Radius of
12 m [40 ft]).................. 698
9-79 Minimum Design of Median Openings (SU Design Vehicle, Control Radius of
15 m [50 ft]).................. 698
9-80 Minimum Design of Median Openings (WB-12 [WB-40] Design Vehicle,
Control Radius of 23 m [75 ft])................... 699
9-81 Minimum Design of Median Openings (SU Design Vehicle, Control Radius
of 15 m [50 ft]).............. 699
9-82 Minimum Design of Median Openings (WB-12 [WB-40]
Design Vehicle, Control Radius of 23 m [75 ft])........................ 700
9-83 Minimum Design of Median Openings (Radius of 30 m [100 ft]) 700
9-84 Minimum Design of Median Openings (Effect of Skew)............ 704
9-85 Design Controls for Minimum Median Openings....................... 705
9-86 Effect of Skew on Minimum Design for Median Openings (Typical Values
Based on Control Radius of 15 m [50 ft]).... 707
9-87 Above Minimum Design of Median Openings (Typical Bullet-Nose Ends) ............. 708
9-88 Jughandle-Type Ramp with Crossroad........ 710
9-89 At-Grade Loop (Surface Loop) with Crossroad.......................... 710
9-90 Special Indirect Left-Turn Designs for Traffic Leaving Highway with
Narrow Median............. 711
9-91 Indirect Left Turn Through a Crossover...... 713
9-92 Minimum Designs for U-turns.................... 715
9-93 Special Indirect U-Turn with Narrow Medians .......................... 716
9-94 Flush or Traversable Median Lane Markings . 717
9-95 Taper Design for Auxiliary Lanes (Metric).. 721
9-96 4.2 to 5.4 m [14 to 18 ft] Median Width Left-Turn Design (Metric) ........................ 723
9-97 Median Left-Turn Design for Median Width in Excess of 5.4 m [18 ft]................... 725
9-98 Parallel and Tapered Offset Left-Turn Lane  728
9-99 Four-Leg Intersection Providing Simultaneous Left Turns.......... 729
9-100 Intersections with Frontage Roads .............. 731
9-101 Cumulative Frequency Distribution of Impact Lengths............... 734
9-102 Railroad-Highway Grade Crossing.............. 736
9-103 Case A:  Moving Vehicle to Safely Cross or Stop at Railroad Crossing ................... 739
9-104 Required Design Sight Distance for Combination of Highway and Train Vehicle
Speeds; 20-m [65-ft] Truck Crossing a Single Set of Tracks at 90° ......................... 741
9-105 Case B:  Departure of Vehicle From Stopped Position to
Cross Single Railroad Track....................... 742xxxviii
10-1 Interchange Configurations......................... 748
10-2 Factors Influencing Length of Access Control Along an Interchange Crossroad....... 754
10-3 Typical Grade Separation Structures With Closed Abutments..... 760
10-4 Typical Grade Separation Structure With Open-End Span.......... 761
10-5 Multilevel Grade Separation Structures....... 762
10-6 Lateral Clearances for Major Roadway Underpasses.................. 766
10-7 Typical Overpass Structures....................... 769
10-8 Flat Terrain, Distance Required to Effect Grade Separation ........ 772
10-9 Three-Leg Interchanges With Single Structures......................... 776
10-10 Three-Leg Interchanges With Multiple Structures...................... 777
10-11 Three-Leg Interchange (T-Type or Trumpet). 778
10-12 Three-Leg Interchange Semidirectional Design.......................... 778
10-13 Directional Three-Leg Interchange of a River Crossing.............. 779
10-14 Trumpet Freeway-to-Freeway Interchange .. 780
10-15 Four-Leg Interchanges, Ramps in One Quadrant........................ 781
10-16 Diamond Interchanges, Conventional Arrangements.................. 783
10-17 Diamond Interchange Arrangements to Reduce Traffic Conflicts 783
10-18 Diamond Interchanges with Additional Structures ..................... 784
10-19 Freeway With a Three-Level Diamond Interchange ................... 785
10-20 Existing Four-Leg Interchange With Diamond Stage Construction.......................... 786
10-21 X-Pattern Ramp Arrangement .................... 786
10-22 Underpass Single Point Urban Interchange.. 788
10-23 An SPUI Underpass in Restricted Right-of-Way........................ 788
10-24 Overpass Layout With a Frontage Road and a Separate U-Turn Movement............. 790
10-25 Underpass SPUI and Overpass SPUI .......... 791
10-26 Four-Leg Interchange, Full Cloverleaf With Collector-Distributor Roads ................ 793
10-27 Cloverleaf Interchange With Collector-Distributor Roads........... 794
10-28 Schematic of Partial Cloverleaf Ramp Arrangements, Exit and Entrance Turns ....... 795
10-29 Four-Leg Interchange (Partial or Two-Quadrant Cloverleaf with Ramps Before
Main Structure) ............. 796
10-30 Four-Leg Interchange (Partial or Two-Quadrant Cloverleaf with Ramps Beyond
Main Structure) ............. 797
10-31 Semidirect Interchanges With Weaving....... 799
10-32 Semidirect Interchanges With No Weaving.. 799
10-33 Semidirectional and Directional Interchanges—Multilevel Structures ..................... 800
10-34 Directional Interchange, Two Semidirect Connections ............... 801
10-35 Four-Level Directional Interchange ............ 801
10-36 Four-Level Directional Interchange ............ 802
10-37 Semidirectional Interchange With Loops ..... 802
10-38 Offset Interchange via Ramp Highway........ 803
10-39 Four-Leg Interchange, Diamond With a Semidirect Connection.. 804
10-40 Four-Leg Interchange, Cloverleaf With a Semidirect Connection 805
10-41 Complex Interchange Arrangement............. 805
10-42 Freeway with a Three-Level Cloverleaf Interchange .................. 806
10-43 Adaptability of Interchanges on Freeways as Related to Types of Intersecting
Facilities ....................... 80810-44 Widening for Divisional Island at Interchanges ......................... 810
10-45 Arrangement of Exits Between Successive Interchanges............ 812
10-46 Interchange Forms to Maintain Route Continuity....................... 812
10-47 Collector-Distributor Road on Major-Minor Roadway Overlap... 814
10-48 Schematic of Basic Number of Lanes ......... 815
10-49 Typical Examples of Lane Balance............. 816
10-50 Coordination of Lane Balance and Basic Number of Lanes........ 817
10-51 Alternative Methods of Dropping Auxiliary Lanes..................... 819
10-52 Coordination of Lane Balance and Basic Number of Lanes Through Application of
Auxiliary Lanes............. 820
10-53 Auxiliary Lane Dropped at Two-Lane Exit.. 821
10-54 Interchange Forms with One and Two Exits  826
10-55 General Types of Ramps 828
10-56 Guide Values for Ramp Design Speed as Related to Highway Design Speed........... 830
10-57 Ramp Shapes ................ 831
10-58 Development of Superelevation at Free-Flow Ramp Terminals... 835
10-59 Typical Gore Area Characteristics .............. 837
10-60 Typical Gore Details ...... 838
10-61 Minimum Length of Taper Beyond an Offset Nose.................... 839
10-62 Traveled-Way Narrowing on Entrance Ramps........................... 839
10-63 Gore Area, Single-Lane Exit....................... 840
10-64 Gore Area, Major Fork... 840
10-65 Gore Area, Two-Lane Exit ......................... 841
10-66 Entrance Terminal......... 841
10-67 Design Widths for Turning Roadways......... 843
10-68 Recommended Minimum Ramp Terminal Spacing..................... 848
10-69 Typical Single-Lane Entrance Ramps ......... 849
10-70 Minimum Acceleration Lengths for Entrance Terminals With Flat Grades of
2 Percent or Less ........... 851
10-71 Speed Change Lane Adjustment Factors as a Function of Grade . 852
10-72 Exit Ramps—Single Lane .......................... 854
10-73 Minimum Deceleration Lengths for Exit Terminals With Flat Grades of
2 Percent or Less........... 855
10-74 Layout of Taper-Type Terminals on Curves (Metric)................. 857
10-75 Parallel-Type Ramp Terminals on Curves ... 859
10-76 Typical Two-Lane Entrance Ramps ............ 862
10-77 Two-Lane Exit Terminals........................... 863
10-78 Major Forks................... 865
10-79 Branch Connections....... 866
10-80 Diagram of Freeway Operational Problem and Solution ............. 868

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