ROAD GEOMETRIC DESIGN MANUAL
(MANUAL A9)
THIRD EDITION
MARCH 2013
Page i
March 2013
Third Edition
Abu Dhabi Department of Transport
Al Bateen Towers
PO Box 20
Abu Dhabi, United Arab Emirates
Copyright 2013, by the Abu Dhabi Department of Transport. All Rights Reserved. This
manual, or parts thereof, may not be reproduced in any form without written permission of
the publisher.
Page ii
DEVELOPMENT TEAM
Department of Transport Technical Committee:
Leader: Nabeel Salman
Members:
Mudar Tayyem
Husam Hammad
Salim Sulaiman
Hesham El Degwy
Hasan Ibrahim
Participating Stakeholders:
Department of Municipal Affairs
Abu Dhabi Police
Urban Planning Council
Abu Dhabi Municipality
Al Ain Municipality
Western Region Municipality
Document Development Consultant:
TrafQuest
PO Box 35701
Dubai
United Arab Emirates
Assisted by:
Roy Jorgensen Associates, Inc.
3735 Buckeystown Pike
PO Box 70
Buckeystown, MD 21717
United States of America
Document Review Consultant:
Aurecon Australia (Pty) Ltd
PO Box 43887
Abu Dhabi
United Arab Emirates
Page iii
TABLE OF CONTENTS
Development Team ............................................................................................................. ii
Table of Contents ............................................................................................................... iii
List of Figures xvii
List of Tables xxiv
Foreword xxix
1 INTRODUCTION TO ROAD DESIGN ......................................................... 1
1.1 Overview .................................................................................................................. 1
1.2 Objectives ................................................................................................................ 1
1.3 Application ............................................................................................................... 2
1.4 Content .................................................................................................................... 2
1.5 References .............................................................................................................. 5
2 GENERAL DESIGN CRITERIA & CONTROL ............................................ 6
2.1 Overview .................................................................................................................. 6
2.2 Context sensitive solutions ....................................................................................... 6
2.3 Sustainability ............................................................................................................ 8
2.4 Functional classification ........................................................................................... 9
2.4.1 Relationship to roadway design ........................................................................ 9
2.4.2 Function of roadway system for rural areas .................................................... 10
2.4.3 Function of roadway system for urban areas .................................................. 13
2.4.4 Urban streets .................................................................................................. 15
2.5 Speed .................................................................................................................... 16
2.5.1 Design speed.................................................................................................. 16
2.5.2 Average running speed ................................................................................... 16
2.5.3 Average travel speed ...................................................................................... 17
2.5.4 Space mean speed ......................................................................................... 17
2.5.5 Operating speed ............................................................................................. 17
2.5.6 Posted speed limit .......................................................................................... 17
2.5.7 Truck/car speed relationship ........................................................................... 18
2.6 Design vehicles ...................................................................................................... 18
2.6.1 Vehicle dimensions ......................................................................................... 18
2.6.2 Turning templates ........................................................................................... 19
2.6.3 Acceleration and deceleration rates ................................................................ 20
2.7 Traffic volume and composition .............................................................................. 20
2.7.1 Design year selection ..................................................................................... 24
Page iv
2.7.2 Traffic characteristics ...................................................................................... 25
2.7.3 Capacity and operational analyses ................................................................. 27
2.8 Environmental considerations ................................................................................ 30
2.9 Right-of-way considerations ................................................................................... 30
2.10 Access control and access management ............................................................... 31
2.11 Non-road design controls ....................................................................................... 32
2.11.1 Drivers ............................................................................................................ 32
2.11.2 Pedestrians and cyclists ................................................................................. 33
2.12 References ............................................................................................................ 34
3 CROSS SECTION ELEMENTS ................................................................ 35
3.1 Overview ................................................................................................................ 35
3.2 Roadway section .................................................................................................... 35
3.2.1 Carriageway ................................................................................................... 35
3.2.2 Travelled way ................................................................................................. 35
3.2.3 Shoulders ....................................................................................................... 41
3.2.4 Rumble strips .................................................................................................. 43
3.2.5 Auxiliary lanes ................................................................................................ 46
3.2.6 Curbs .............................................................................................................. 47
3.3 Medians ................................................................................................................. 50
3.3.1 Functions ........................................................................................................ 50
3.3.2 Median widths ................................................................................................. 51
3.3.3 Median types .................................................................................................. 53
3.3.4 Median selection ............................................................................................. 56
3.4 Roadside elements ................................................................................................ 57
3.4.1 Verges ............................................................................................................ 57
3.4.2 Side slopes ..................................................................................................... 57
3.4.3 Sidewalks/pathways ....................................................................................... 63
3.4.4 Bicycles .......................................................................................................... 63
3.4.5 Clear zones/clearances .................................................................................. 63
3.5 Traffic barriers ........................................................................................................ 63
3.6 Noise control .......................................................................................................... 65
3.7 Sand control ........................................................................................................... 66
3.7.1 General ........................................................................................................... 66
3.7.2 Sand movement and deposition...................................................................... 66
3.7.3 Location .......................................................................................................... 67
Page v
3.7.4 Design elements ............................................................................................. 68
3.7.5 Dune stabilization ........................................................................................... 69
3.7.6 Dune destruction ............................................................................................ 71
3.8 Right-of-way ........................................................................................................... 72
3.9 Utilities ................................................................................................................... 72
3.9.1 Types ............................................................................................................. 72
3.9.2 Location .......................................................................................................... 73
3.9.3 Design considerations .................................................................................... 74
3.10 Tunnels .................................................................................................................. 74
3.10.1 Types of tunnels ............................................................................................. 75
3.10.2 Tunnel cross sections ..................................................................................... 77
3.11 References ............................................................................................................ 79
4 SIGHT DISTANCE .................................................................................... 80
4.1 Overview ................................................................................................................ 80
4.2 Eye and object heights ........................................................................................... 80
4.3 Stopping sight distance .......................................................................................... 81
4.3.1 Passenger cars (level grade) .......................................................................... 81
4.3.2 Grade-adjusted SSD ....................................................................................... 82
4.3.3 Trucks............................................................................................................. 83
4.3.4 SSD application .............................................................................................. 84
4.4 Decision sight distance .......................................................................................... 85
4.4.1 Theoretical discussion .................................................................................... 85
4.4.2 Applications .................................................................................................... 86
4.5 Passing sight distance ........................................................................................... 87
4.6 Intersection sight distance ...................................................................................... 89
4.6.1 General ........................................................................................................... 89
4.6.2 Eye and object heights ................................................................................... 90
4.6.3 Case A Intersections with no control ............................................................ 90
4.6.4 Case B Intersections with stop control on the minor road ............................. 90
4.6.5 Case C Intersections with yield control on the minor road ............................ 95
4.6.6 Case D Intersections with traffic signal control ............................................. 98
4.6.7 Case EIntersections with all-way stop control .............................................. 99
4.6.8 Case F Left turns from the major road ......................................................... 99
4.6.9 Examples of ISD applications ....................................................................... 102
4.6.10 Effect of skew ............................................................................................... 106
Page vi
4.7 References .......................................................................................................... 108
5 HORIZONTAL ALIGNMENT .................................................................. 109
5.1 Overview .............................................................................................................. 109
5.2 Horizontal curves ................................................................................................. 109
5.2.1 Types of horizontal curves ............................................................................ 109
5.2.2 General theory .............................................................................................. 112
5.2.3 Minimum radii ............................................................................................... 114
5.2.4 Maximum deflection without curve ................................................................ 114
5.2.5 Minimum length of curve ............................................................................... 115
5.3 Superelevation development ................................................................................ 116
5.3.1 Superelevation rates ..................................................................................... 116
5.3.2 Transition lengths ......................................................................................... 117
5.3.3 Application of transition length ...................................................................... 125
5.3.4 Axis of rotation .............................................................................................. 126
5.3.5 Shoulder superelevation ............................................................................... 127
5.3.6 Compound curves ........................................................................................ 129
5.3.7 Reverse curves ............................................................................................. 130
5.3.8 Superelevation development figures ............................................................. 131
5.4 Spiral curves ........................................................................................................ 131
5.4.1 Application .................................................................................................... 141
5.4.2 Length of spiral ............................................................................................. 144
5.4.3 Length of superelevation runoff .................................................................... 145
5.4.4 Limiting superelevation rates ........................................................................ 146
5.4.5 Length of tangent runout ............................................................................... 146
5.5 Horizontal sight distance ...................................................................................... 146
5.5.1 Overview ...................................................................................................... 146
5.5.2 Equations ..................................................................................................... 147
5.5.3 Eye and object heights ................................................................................. 150
5.6 Curve widening .................................................................................................... 150
5.6.1 General theory .............................................................................................. 150
5.6.2 Design values ............................................................................................... 153
5.6.3 Application .................................................................................................... 155
5.7 General controls for horizontal alignment ............................................................. 155
5.8 References .......................................................................................................... 158
6 VERTICAL ALIGNMENT ........................................................................ 159
Page vii
6.1 Overview .............................................................................................................. 159
6.2 Grades and terrain ............................................................................................... 159
6.2.1 Terrain/topography ....................................................................................... 159
6.2.2 Maximum grades .......................................................................................... 159
6.2.3 Minimum grades ........................................................................................... 159
6.2.4 Trucks........................................................................................................... 160
6.2.5 Critical length of grade .................................................................................. 160
6.3 Truck-climbing lanes ............................................................................................ 166
6.3.1 Location guidelines ....................................................................................... 167
6.3.2 Capacity analysis .......................................................................................... 168
6.3.3 Design guidelines ......................................................................................... 168
6.3.4 Downgrades ................................................................................................. 172
6.4 Vertical curves ..................................................................................................... 172
6.4.1 Crest vertical curves ..................................................................................... 172
6.4.2 Sag vertical curves ....................................................................................... 178
6.4.3 Vertical curve computations .......................................................................... 183
6.5 Minimum vertical clearances ................................................................................ 185
6.6 Alignment and profile relationships....................................................................... 190
6.6.1 General controls for vertical alignment .......................................................... 190
6.6.2 Coordination of horizontal and vertical alignment .......................................... 192
6.6.3 Alignment coordination figures ...................................................................... 193
6.6.4 Profile grade lines ......................................................................................... 202
6.7 Emergency escape ramps ................................................................................... 202
6.7.1 Purpose and need ........................................................................................ 202
6.7.2 Containment facilities .................................................................................... 203
6.7.3 Warrant for investigation ............................................................................... 203
6.7.4 Location and spacing .................................................................................... 204
6.7.5 Design process ............................................................................................. 205
6.7.6 Brake check areas ........................................................................................ 211
6.7.7 Maintenance ................................................................................................. 211
6.8 References .......................................................................................................... 212
7 RURAL AND URBAN FREEWAYS ........................................................ 213
7.1 Overview .............................................................................................................. 213
7.2 Freeway systems ................................................................................................. 213
7.2.1 Basic components ........................................................................................ 213
Page viii
7.2.2 Freeway spacing .......................................................................................... 214
7.2.3 Network configurations ................................................................................. 214
7.2.4 Linear freeway systems configurations ......................................................... 215
7.3 Freeway types...................................................................................................... 218
7.3.1 Ground-level freeways .................................................................................. 218
7.3.2 Depressed freeways ..................................................................................... 221
7.3.3 Elevated freeways ........................................................................................ 222
7.3.4 Combination-type freeways .......................................................................... 224
7.3.5 Special freeway designs ............................................................................... 227
7.4 General design considerations ............................................................................. 231
7.4.1 Design speed................................................................................................ 231
7.4.2 Design traffic volumes .................................................................................. 231
7.4.3 Capacity analysis .......................................................................................... 232
7.4.4 Travelled way and shoulders ........................................................................ 233
7.4.5 Curbs ............................................................................................................ 234
7.4.6 Superelevation .............................................................................................. 234
7.4.7 Grades.......................................................................................................... 234
7.4.8 Structures ..................................................................................................... 234
7.4.9 Vertical clearance ......................................................................................... 235
7.4.10 Roadside design ........................................................................................... 235
7.4.11 Ramps and terminals .................................................................................... 235
7.4.12 Outer separations and borders ..................................................................... 235
7.4.13 Access control .............................................................................................. 236
7.5 Grade separation design ...................................................................................... 237
7.5.1 Justification ................................................................................................... 237
7.5.2 Design .......................................................................................................... 238
7.6 Rural freeways ..................................................................................................... 243
7.6.1 Alignment and profile .................................................................................... 243
7.6.2 Medians ........................................................................................................ 245
7.6.3 Side slopes ................................................................................................... 246
7.6.4 Service roads ................................................................................................ 247
7.7 Urban freeways .................................................................................................... 247
7.7.1 General design characteristics ...................................................................... 247
7.7.2 Medians ........................................................................................................ 247
7.7.3 Service roads ................................................................................................ 248
Page ix
7.7.4 Managed lanes ............................................................................................. 250
7.8 References .......................................................................................................... 253
8 RURAL ROADS ..................................................................................... 254
8.1 Overview .............................................................................................................. 254
8.2 Two-lane roads .................................................................................................... 254
8.2.1 General characteristics ................................................................................. 254
8.2.2 General design considerations ..................................................................... 254
8.2.3 Cross section elements ................................................................................ 261
8.2.4 Structures ..................................................................................................... 262
8.2.5 Provision for passing .................................................................................... 262
8.2.6 Ultimate development for a dual carriageway ............................................... 264
8.2.7 Turnouts ....................................................................................................... 265
8.3 Rural multilane roads ........................................................................................... 267
8.3.1 General design considerations ..................................................................... 270
8.3.2 Cross sectional elements .............................................................................. 271
8.3.3 Structures ..................................................................................................... 273
8.3.4 Intersections ................................................................................................. 273
8.3.5 Access management .................................................................................... 274
8.4 Trucks .................................................................................................................. 274
8.5 References .......................................................................................................... 276
9 URBAN STREETS.................................................................................. 277
9.1 Overview .............................................................................................................. 277
9.2 General ................................................................................................................ 277
9.2.1 Urban design challenges .............................................................................. 277
9.2.2 Urban street typology .................................................................................... 278
9.2.3 Access management .................................................................................... 279
9.3 General design elements ..................................................................................... 279
9.3.1 Design speed................................................................................................ 279
9.3.2 Capacity analyses ........................................................................................ 279
9.3.3 Sight distance ............................................................................................... 284
9.3.4 Alignment ..................................................................................................... 284
9.3.5 Grades.......................................................................................................... 284
9.3.6 Cross section elements ................................................................................ 285
9.3.7 Traffic control devices ................................................................................... 294
9.3.8 Structures ..................................................................................................... 294
Page x
9.3.9 Intersections ................................................................................................. 294
9.3.10 Drainage ....................................................................................................... 295
9.4 Horizontal alignment ............................................................................................ 295
9.4.1 Superelevation methodology ........................................................................ 295
9.4.2 General superelevation considerations ......................................................... 295
9.4.3 Maximum superelevation rate ....................................................................... 296
9.4.4 Minimum radii ............................................................................................... 296
9.4.5 Maximum deflection without curve ................................................................ 297
9.4.6 Transition lengths ......................................................................................... 297
9.4.7 Axis of rotation .............................................................................................. 298
9.4.8 Typical designs ............................................................................................. 298
9.5 Tables of design criteria ....................................................................................... 298
9.6 References .......................................................................................................... 319
10 INTERSECTIONS ................................................................................... 320
10.1 Overview .............................................................................................................. 320
10.2 General design controls ....................................................................................... 320
10.2.1 General design considerations ..................................................................... 320
10.2.2 Intersection components ............................................................................... 321
10.2.3 Intersection capacity ..................................................................................... 324
10.2.4 Intersection types ......................................................................................... 326
10.2.5 Intersection spacing ...................................................................................... 329
10.2.6 Intersection alignment ................................................................................... 332
10.2.7 Profiles ......................................................................................................... 335
10.2.8 Design vehicles ............................................................................................ 336
10.2.9 Pedestrians and cyclists ............................................................................... 337
10.2.10 Signing and pavement markings ............................................................. 337
10.2.11 Drainage ................................................................................................. 338
10.3 Corner radii .......................................................................................................... 338
10.3.1 Design for right-turning vehicles.................................................................... 339
10.3.2 Left-turn control radii ..................................................................................... 351
10.4 Rural turning roadways/urban slip lanes............................................................... 355
10.4.1 Guidelines .................................................................................................... 355
10.4.2 Design .......................................................................................................... 355
10.4.3 Rural turning lane widths .............................................................................. 360
10.4.4 Horizontal alignment ..................................................................................... 362
Page xi
10.4.5 Right-angle turns with corner islands ............................................................ 366
10.4.6 Oblique-angle turns with corner islands ........................................................ 366
10.4.7 Deceleration/acceleration lanes .................................................................... 367
10.5 Channelization ..................................................................................................... 368
10.5.1 Guidance ...................................................................................................... 368
10.5.2 Design considerations .................................................................................. 369
10.6 Islands ................................................................................................................. 372
10.6.1 Island types .................................................................................................. 372
10.6.2 Selection of island type ................................................................................. 373
10.6.3 Design of islands .......................................................................................... 374
10.6.4 Refuge islands .............................................................................................. 377
10.6.5 Corner islands .............................................................................................. 378
10.6.6 Island size and designation ........................................................................... 380
10.7 Auxiliary turn lanes ............................................................................................... 381
10.7.1 Warrants ....................................................................................................... 381
10.7.2 Design of turn lanes ...................................................................................... 385
10.7.3 Left-turn lane designs ................................................................................... 389
10.7.4 Right-turn lanes ............................................................................................ 397
10.7.5 Multiple turn lanes ........................................................................................ 399
10.8 Median openings .................................................................................................. 402
10.8.1 Location/spacing ........................................................................................... 402
10.8.2 Design .......................................................................................................... 402
10.8.3 Minimum design for U-turns .......................................................................... 408
10.9 Placement of bus stops near intersections ........................................................... 408
10.10 Frontage roads..................................................................................................... 412
10.11 References .......................................................................................................... 414
11 ROUNDABOUTS .................................................................................... 415
11.1 Overview .............................................................................................................. 415
11.2 Characteristics of a roundabout ........................................................................... 415
11.2.1 Design features ............................................................................................ 415
11.2.2 Roundabouts types ....................................................................................... 415
11.3 Categories of roundabouts ................................................................................... 417
11.3.1 Mini-roundabouts .......................................................................................... 420
11.3.2 Single-lane roundabouts ............................................................................... 421
11.3.3 Multilane roundabouts .................................................................................. 422
Page xii
11.4 Roundabout Considerations ................................................................................. 422
11.4.1 Planning ....................................................................................................... 422
11.4.2 General roundabout characteristics .............................................................. 422
11.4.3 User considerations ...................................................................................... 425
11.4.4 Policy and legal issues ................................................................................. 425
11.4.5 Access management .................................................................................... 426
11.5 Operational analysis ............................................................................................ 426
11.5.1 Introduction ................................................................................................... 426
11.5.2 Principles ...................................................................................................... 427
11.5.3 Data collection .............................................................................................. 428
11.5.4 Analysis techniques ...................................................................................... 428
11.5.5 Highway capacity manual method ................................................................ 429
11.6 Safety .................................................................................................................. 431
11.7 Geometric design ................................................................................................. 432
11.7.1 Introduction ................................................................................................... 432
11.7.2 Principles and objectives .............................................................................. 433
11.7.1 Speed management ..................................................................................... 434
11.7.2 Lane arrangements....................................................................................... 436
11.7.3 Path alignment .............................................................................................. 436
11.7.4 Size, position, and alignment ........................................................................ 437
11.7.5 Single-lane roundabouts ............................................................................... 440
11.7.6 Multilane roundabouts .................................................................................. 443
11.7.7 Mini-roundabouts .......................................................................................... 446
11.7.8 Closely spaced roundabouts ......................................................................... 448
11.8 Other considerations ............................................................................................ 448
11.8.1 Traffic control devices ................................................................................... 448
11.8.2 Landscaping ................................................................................................. 449
11.8.3 Illumination ................................................................................................... 449
11.9 References .......................................................................................................... 451
12 INTERCHANGES ................................................................................... 452
12.1 Overview .............................................................................................................. 452
12.2 Warrants .............................................................................................................. 452
12.3 General design considerations ............................................................................. 453
12.3.1 System and service interchanges ................................................................. 453
12.3.2 Interchange spacing ..................................................................................... 457
Page xiii
12.3.3 Distance between successive freeway/ramp junctions .................................. 457
12.3.4 Basic number of lanes .................................................................................. 457
12.3.5 Lane balance ................................................................................................ 457
12.3.6 Capacity and level of service ........................................................................ 460
12.3.7 Auxiliary lanes .............................................................................................. 461
12.3.8 Freeway lane drops ...................................................................................... 464
12.3.9 Route continuity ............................................................................................ 466
12.3.10 Uniformity ............................................................................................... 466
12.3.11 Left-hand ramps...................................................................................... 466
12.3.12 Signing and marking ............................................................................... 466
12.3.13 Weaving sections .................................................................................... 466
12.3.14 Grading and landscaping ........................................................................ 468
12.3.15 Review for ease of operation .................................................................. 468
12.3.16 Geometric design criteria ........................................................................ 468
12.3.17 Operational/safety considerations ........................................................... 472
12.4 Interchange types and layouts ............................................................................. 474
12.4.1 General ......................................................................................................... 474
12.4.2 Diamond interchange .................................................................................... 474
12.4.3 Modified diamond ......................................................................................... 479
12.4.4 Compressed diamond ................................................................................... 482
12.4.5 Single-point diamond interchange ................................................................. 485
12.4.6 Full cloverleaf ............................................................................................... 488
12.4.7 Partial cloverleafs ......................................................................................... 493
12.4.8 Trumpet interchange ..................................................................................... 502
12.4.9 Direct and semi-direct interchanges .............................................................. 506
12.4.10 Other Interchange types ......................................................................... 510
12.4.11 Selection ................................................................................................. 516
12.5 Ramp design ........................................................................................................ 517
12.5.1 Ramp types .................................................................................................. 517
12.5.2 Collector-distributor roadways ...................................................................... 519
12.5.3 High-speed direct/semi-direct roadways ....................................................... 521
12.5.4 Design speed................................................................................................ 522
12.5.5 Sight distance ............................................................................................... 523
12.5.6 Cross section elements ................................................................................ 523
12.5.7 Two-lane loop ramps .................................................................................... 527
Page xiv
12.5.8 Horizontal alignment ..................................................................................... 527
12.5.9 Vertical alignment ......................................................................................... 530
12.5.10 Roadside safety ...................................................................................... 531
12.5.11 Ramp capacity ........................................................................................ 531
12.5.12 Ramp Metering ....................................................................................... 531
12.6 Freeway ramp terminals ....................................................................................... 532
12.6.1 Exit ramp terminals ....................................................................................... 532
12.6.2 Entrance ramps ............................................................................................ 538
12.6.3 Capacity analysis .......................................................................................... 543
12.7 Ramp/crossroad intersections .............................................................................. 544
12.7.1 General design criteria .................................................................................. 544
12.7.2 Slip ramp designs ......................................................................................... 545
12.7.3 Crossroad access control ............................................................................. 548
12.8 Ramp/freeway divergence and convergence ....................................................... 549
12.8.1 Divergences ................................................................................................. 549
12.8.2 Convergences .............................................................................................. 550
12.8.3 Manoeuvre areas .......................................................................................... 550
12.9 HOV and public transport ..................................................................................... 552
12.10 Toll road facilities ................................................................................................. 553
12.11 References .......................................................................................................... 554
13 PEDESTRIAN AND BICYCLIST FACILITIES ........................................ 555
13.1 Overview .............................................................................................................. 555
13.2 Pedestrians .......................................................................................................... 555
13.2.1 Public Realm ................................................................................................ 555
13.2.2 Pedestrian realm zones ................................................................................ 555
13.2.3 Design guidance ........................................................................................... 558
13.3 Cyclists ................................................................................................................ 569
13.3.1 Definitions ..................................................................................................... 569
13.3.2 Bicycle facilities at intersections .................................................................... 570
13.3.3 Cycle parking ................................................................................................ 571
13.3.4 Separate cycle facilities ................................................................................ 571
13.4 References .......................................................................................................... 575
14 RAILWAY CROSSINGS ......................................................................... 576
14.1 Overview .............................................................................................................. 576
14.2 Geometric design elements.................................................................................. 576
Page xv
14.2.1 General guidance ......................................................................................... 576
14.2.2 Sight distance ............................................................................................... 576
14.2.3 Horizontal alignment ..................................................................................... 581
14.2.4 Vertical alignment ......................................................................................... 581
14.2.5 Surface design .............................................................................................. 581
14.2.6 Intersections design near railroad crossings ................................................. 582
14.3 Traffic control devices .......................................................................................... 582
14.4 Light rail transit track in mixed traffic .................................................................... 582
14.4.1 Introduction ................................................................................................... 582
14.4.2 Track position within lanes ............................................................................ 583
14.5 References .......................................................................................................... 585
15 INTELLIGENT TRANSPORT SYSTEMS ................................................ 586
15.1 Overview .............................................................................................................. 586
15.2 ITS design ............................................................................................................ 586
15.3 Systems engineering............................................................................................ 586
15.4 Vehicle detection stations .................................................................................... 587
15.4.1 General ......................................................................................................... 587
15.4.2 Types of detection ........................................................................................ 587
15.5 Traffic data collection ........................................................................................... 588
15.6 Closed circuit television systems .......................................................................... 588
15.7 Road weather monitoring systems ....................................................................... 589
15.8 Help phone systems ............................................................................................ 590
15.9 Variable message signs ....................................................................................... 590
15.10 Ramp metering systems ...................................................................................... 591
15.11 Weigh-in-motion systems ..................................................................................... 591
15.12 Automatic number plate recognition systems ....................................................... 592
15.13 Tunnel management systems .............................................................................. 592
15.14 References .......................................................................................................... 594
16 ROADSIDE AMENITY ............................................................................ 595
16.1 Overview .............................................................................................................. 595
16.2 Visual amenity and aesthetics .............................................................................. 595
16.2.1 Introduction ................................................................................................... 595
16.2.2 Importance ................................................................................................... 595
16.2.3 Objectives ..................................................................................................... 596
16.2.4 Aesthetics and visual impact assessment ..................................................... 596
Page xvi
16.2.5 Documenting and reviewing visual impacts .................................................. 598
16.3 Landscaping ........................................................................................................ 600
16.3.1 Landscape design principles ......................................................................... 600
16.3.2 Overview of landscape design process ......................................................... 603
16.3.3 Responsibility for preparation of design ........................................................ 603
16.3.4 Design factors ............................................................................................... 604
16.4 Roadway lighting .................................................................................................. 606
16.4.1 Utility poles ................................................................................................... 606
16.4.2 Facilities ....................................................................................................... 607
16.5 Fencing ................................................................................................................ 607
16.5.1 General ......................................................................................................... 607
16.5.2 Freeways and expressways .......................................................................... 608
16.5.3 Pedestrian fencing ........................................................................................ 609
16.5.4 Protective fencing on roadway overpasses ................................................... 610
16.5.5 Fencing or safety devices on top of retaining walls ....................................... 610
16.6 Rest areas ........................................................................................................... 610
16.6.1 General ......................................................................................................... 610
16.6.2 Location of rest areas ................................................................................... 611
16.6.3 Design of rest areas ...................................................................................... 614
16.7 Oasis ................................................................................................................... 623
16.8 Truck lay-by ......................................................................................................... 624
16.9 Off-street parking ................................................................................................. 625
16.9.1 Park-and-ride lots ......................................................................................... 626
16.9.2 Design elements ........................................................................................... 627
16.10 References .......................................................................................................... 633
16.11 Definitions ............................................................................................................ 634
16.12 Geometric qualifying words .................................................................................. 659
16.13 Acronyms ............................................................................................................. 659
Page xvii
LIST OF FIGURES
Figure 2-1: Relationship of functionally classified systems in serving traffic mobility and land access (1) ................................................................................. 10
Figure 2-2: Basic dimension of tractorsemitrailer vehicle ........................................... 22
Figure 2-3: Basic dimension of tractor semitrailer vehicle/ trailer vehicle (double trailer) ...................................................................................................... 23
Figure 2-4: Turning characteristics of a typical semitrailer design vehicle (1) ............. 24
Figure 3-1: Rural dual carriageway nomenclature .......................................................... 36
Figure 3-2: Urban dual carriageway (freeways) nomenclature ...................................... 37
Figure 3-3: Rural single carriageway nomenclature ....................................................... 38
Figure 3-4: City boulevard nomenclature (4) ................................................................... 39
Figure 3-5: City avenue nomenclature (4) ....................................................................... 40
Figure 3-6: Rumble strip types (18) ................................................................................. 44
Figure 3-7: Shoulder rumble strip locations (19) ............................................................ 45
Figure 3-8: Vertical curb design ....................................................................................... 48
Figure 3-9: Typical curb types (17) .................................................................................. 49
Figure 3-10: Typical median types ................................................................................... 54
Figure 3-11: Typical ditch section .................................................................................... 59
Figure 3-12: Typical cut sections with curbs .................................................................. 60
Figure 3-13: Typical rock cut section .............................................................................. 62
Figure 3-14: Details of concrete median barrier ............................................................. 64
Figure 3-15: Example cast-in-place curb to concrete barrier transition ........................ 65
Figure 3-16: Sand dunes .................................................................................................. 69
Figure 3-17: Stabilizing dunes (23) .................................................................................. 71
Figure 3-18: Abu Dhabi Tunnels ...................................................................................... 75
Figure 3-19: Tunnel cross section ................................................................................... 78
Figure 4-1: Clear sight triangle for viewing traffic approaching from left ..................... 91
Figure 4-2: Clear sight triangle for viewing traffic approaching from right .................. 91
Figure 4-3: Approach sight triangles (yield control) (1) ................................................. 97
Figure 4-4: Intersection sight distance (left turns from the major road) ..................... 100
Figure 4-5: Example 4.6 1 ............................................................................................ 102
Figure 4-6: Example 4.6 2 ............................................................................................ 104
Figure 4-7: Example 4.6 3 ............................................................................................ 105
Figure 4-8: Sight distance at skewed intersections ...................................................... 107
Figure 5-1: Simple curve nomenclature ........................................................................ 111
Figure 5-2: Three-centred compound curve .................................................................. 111
Figure 5-3: Comparison of side-friction factors (2) ...................................................... 113
Figure 5-4: Method of distributing superelevation and side friction (1) ...................... 114
Figure 5-5: Superelevation transition length ................................................................. 121
Page xviii
Figure 5-6: Shoulder treatment through superelevated curve ..................................... 128
Figure 5-7: Reverse curves to parallel tangents ........................................................... 132
Figure 5-8: Reverse curves (tangents not parallel) ....................................................... 133
Figure 5-9: Superelevation development for reverse curves ....................................... 134
Figure 5-10: Axis of rotation about centreline (single carriageway)............................ 135
Figure 5-11: Axis of rotation about inside edge (single carriageway) ........................ 136
Figure 5-12: Axis of rotation about outside edge (single carriageway) ...................... 137
Figure 5-13: Axis of rotation for dual carriageway (depressed median) ..................... 138
Figure 5-14: Axis of rotation for dual carriageway (raised median) ........................... 139
Figure 5-15: Axis of rotation about centreline (compound curves) ............................. 140
Figure 5-16: Spiral curve nomenclature (3) ................................................................... 142
Figure 5-17: Sight clearance requirements for horizontal curves (L > S) ................... 148
Figure 5-18: Sight clearance requirements for horizontal curves (S > L) ................... 149
Figure 5-19: Sight distance at horizontal curves (SSD)................................................ 151
Figure 5-20: Widening components on open roadway curves (1) ............................... 153
Figure 5-21: Horizontal curve coordination................................................................... 157
Figure 6-1: Critical length of grade (trucks) (1) ............................................................ 161
Figure 6-2: Measurement for length of grade ............................................................... 163
Figure 6-3: Example 6.2-2 .............................................................................................. 164
Figure 6-4: Critical length of grade calculations (Example 6.2-3) ............................... 165
Figure 6-5: Truck climbing lane .................................................................................... 167
Figure 6-6: Truck climbing lane .................................................................................... 169
Figure 6-7: Performance curves for a typical heavy truck (120 kg/kW) (1) ................ 171
Figure 6-8: Symmetrical vertical curve equation ......................................................... 186
Figure 6-9: Unsymmetrical vertical curve equations ................................................... 188
Figure 6-10: Plan and profile sheet ................................................................................ 191
Figure 6-11: Horizontal and vertical alignment coordination ...................................... 195
Figure 6-12: Examples of undesirable and good alignment coordination ................. 196
Figure 6-13: Combined alignment designs to avoid .................................................... 198
Figure 6-14: Superimposition of horizontal and vertical alignments ......................... 200
Figure 6-15: Examples of superimposition of horizontal and vertical alignments .... 201
Figure 6-16: An example of an arrester bed layout (2) ................................................ 209
Figure 7-1: Basic freeway networks (32) ....................................................................... 215
Figure 7-2: Linear freeway system configurations (32) ................................................ 217
Figure 7-3: Typical freeway at ground level (TrafQuest) .............................................. 218
Figure 7-4: Typical ground level freeway (TrafQuest) .................................................. 219
Figure 7-5: Typical cross sections for ground-level freeways (1) ............................... 220
Figure 7-6: Restricted cross sections for ground-level freeways (1) .......................... 220
Figure 7-7: Cross sections for depressed freeways (1)................................................ 222
Page xix
Figure 7-8: Typical viaduct cross sections for elevated freeways (1) ......................... 225
Figure 7-9: Typical embankment cross sections for elevated freeways (1) ................ 225
Figure 7-10: Combination freeway in rolling terrain (1) ................................................ 226
Figure 7-11: Profile control combination-type freeway in level terrain (1) ............. 226
Figure 7-12: Combination-type freeways with restricted right-of-way (1) ................... 228
Figure 7-13: Typical cross sections for reverse-flow operation (1) ............................. 228
Figure 7-14: Typical cross sections for dual-divided operation (1) ............................. 229
Figure 7-15: Typical freeway with C-D road (TrafQuest) .............................................. 230
Figure 7-16: Typical cross sections for underpasses (32) ........................................... 239
Figure 7-17: Grade separation determination (1) .......................................................... 242
Figure 7-18: Typical rural medians (1) ........................................................................... 246
Figure 7-19. Bus roadway located between a freeway and a parallel service road (1)251
Figure 7-20: Joint freeway-transit right-of-way (1) ........................................................ 252
Figure 8-1: Typical two-lane road (TrafQuest) .............................................................. 255
Figure 8-2: LOS on base speed-flow curves ................................................................. 260
Figure 8-3: Passing lanes on a two-way, single carriageway ...................................... 264
Figure 8-4: Single carriageway cross section with ultimate development to dual carriageway ........................................................................................... 266
Figure 9-1: Typical city boulevard (with frontage lane) (4) ........................................... 286
Figure 9-2: Typical City Avenue (4) ................................................................................ 287
Figure 9-3: Typical city street (4) ................................................................................... 288
Figure 9-4: Typical city access lane (4) ......................................................................... 288
Figure 9-5: Typical city boulevard (4) ............................................................................ 289
Figure 9-6: Superelevation rates (low-speed urban streets) ........................................ 297
Figure 10-1: Physical and functional intersection area (1) ........................................... 322
Figure 10-2: Typical intersection components ............................................................. 323
Figure 10-3: Three-leg intersection (Google Earth) ...................................................... 327
Figure 10-4: Four-leg intersection ................................................................................. 328
Figure 10-5: Roundabout (Google Earth) ...................................................................... 329
Figure 10-6: Signalised intersection spacing guidelines (48) ...................................... 331
Figure 10-7: Angled intersection (Google Earth) .......................................................... 332
Figure 10-8: Realignment of intersections (1) ............................................................... 334
Figure 10-9: Offset intersection ..................................................................................... 335
Figure 10-10: Intersection gradient check points ......................................................... 336
Figure 10-11: Allowable encroachment on a local road ............................................... 340
Figure 10-12: Allowable turning encroachment onto a multilane route ...................... 341
Figure 10-13: Shoulder/curb radius return transitions ................................................. 343
Figure 10-14: Three-centred compound radii ................................................................ 344
Figure 10-15: Effect of curb radii and shoulders on rural right-turning paths ............ 352
Page xx
Figure 10-16: Summary of right-turn design issues ..................................................... 353
Figure 10-17: Left-turn control radii ............................................................................... 354
Figure 10-18: Use of simple and compound curves at free-flow turning roadways ... 356
Figure 10-19: Typical rural turning roadway layout ...................................................... 357
Figure 10-20: Typical urban slip lane layouts (4) .......................................................... 358
Figure 10-21: Superelevation development of rural turning roadway (mainline on tangent or curved to the right) (1) ........................................................ 364
Figure 10-22: Superelevation development of rural turning road (mainline curved to the left) (1) ............................................................................................. 365
Figure 10-23: Examples of a channelized intersections ............................................... 371
Figure 10-24: Channelized island ................................................................................... 372
Figure 10-25: Typical channelizing island design ......................................................... 376
Figure 10-26: Crosswalk through centre island (4)....................................................... 377
Figure 10-27: Details of corner islands .......................................................................... 379
Figure 10-28: Guidelines for right-turn lanes at unsignalised intersections on two-way single carriageway (49) ......................................................................... 383
Figure 10-29: Guidelines for right-turn lanes at unsignalised intersection on dual carriageway (80 km/h or greater) (49) .................................................. 384
Figure 10-30: Typical auxiliary lanes at intersections .................................................. 387
Figure 10-31: Examples of taper designs (1) ................................................................. 388
Figure 10-32: Flush channelized islands at isolated high-speed rural intersection ... 391
Figure 10-33: Raised channelized intersection (parallel left-turn lane) ....................... 392
Figure 10-34: Parallel and tapered offset left-turn lane ................................................ 394
Figure 10-35 Typical design for parallel offset left-turn lanes ..................................... 395
Figure 10-36: Expressway or multilane facility with median width 12 m (tapered offset left-turn lane design) .................................................................. 396
Figure 10-37: Example of parallel offset design for left-turn lanes (Google Earth) .... 397
Figure 10-38: Four-leg intersection providing simultaneous left turns ....................... 398
Figure 10-39: Pedestrian refuge at multiple left-turn lanes (4)..................................... 399
Figure 10-40: Schematic for dual left-turn lanes ........................................................... 401
Figure 10-41: Median opening design ........................................................................... 403
Figure 10-42: Median nose design ................................................................................. 407
Figure 10-43: Curb side bus stops near right-in, right-out junction (69) ..................... 411
Figure 10-44: Curb side bus stops near roundabout (69) ............................................ 411
Figure 10-45: Curb side bus stops at urban signal junction (69) ................................. 412
Figure 10-46: Intersections with frontage roads (1) ...................................................... 413
Figure 11-1: Roundabout characteristics (50) ............................................................... 416
Figure 11-2: Roundabout for freeway ramp and crossroad ......................................... 419
Figure 11-3: Single lane roundabout (Google Earth) .................................................... 419
Figure 11-4: Multilane roundabout ................................................................................. 419
Page xxi
Figure 11-5: Features of typical mini-roundabout ........................................................ 420
Figure 11-6: Features of typical single-lane roundabout (50) ...................................... 421
Figure 11-7: Features of typical two-lane roundabout (50) .......................................... 423
Figure 11-8: Features of typical three-lane roundabout (50) ........................................ 423
Figure 11-9: Geometric elements of an urban roundabout (50) ................................... 435
Figure 11-10: Single-lane roundabout (Google Earth) .................................................. 440
Figure 11-11: Typical minimum splitter island nose radii and offsets (50) ................. 442
Figure 11-12: Multi-lane roundabout (Google Earth) .................................................... 444
Figure 12-1: System and service types (1) .................................................................... 454
Figure 12-2: Service interchange (Google Earth) ......................................................... 455
Figure 12-3: Service interchange (Google Earth) ......................................................... 455
Figure 12-4: System interchange (Google Earth) ......................................................... 456
Figure 12-5: Ramp terminal spacing and guidelines (1) ............................................... 458
Figure 12-6: Coordination of lane balance and basic number of lanes (1) ................. 459
Figure 12-7: Individual elements of an interchange (13) .............................................. 461
Figure 12-8: Auxiliary lanes within an interchange (1) ................................................. 462
Figure 12-9: Auxiliary lanes between two interchanges............................................... 463
Figure 12-10: Typical freeway lane drop (right side) .................................................... 465
Figure 12-11: Weaving Influence area (13) .................................................................... 467
Figure 12-12: Ramp terminals on curved roads (51) .................................................... 470
Figure 12-13: Diamond interchange .............................................................................. 475
Figure 12-14: Double roundabout diamond (dumbbell) interchange .......................... 478
Figure 12-15: Split diamond interchanges .................................................................... 480
Figure 12-16: Modified diamond interchange ............................................................... 481
Figure 12-17: Compressed diamond interchange ......................................................... 482
Figure 12-18: Compressed diamond with turnaround .................................................. 484
Figure 12-19: Single-point urban diamond interchange ............................................... 485
Figure 12-20: Cloverleaf interchanges........................................................................... 490
Figure 12-21: Cloverleaf interchanges........................................................................... 491
Figure 12-22: Cloverleaf interchange layout ................................................................. 492
Figure 12-23: Partial cloverleaf interchange layout (Google earth) ............................. 494
Figure 12-24: Partial cloverleaf interchange layout (two quadrants Type A) ........... 495
Figure 12-25: Partial cloverleaf interchange layout (two-quadrant Type B) ............. 496
Figure 12-26: Partial cloverleaf interchange layout (two-quadrant Type C) ............. 497
Figure 12-27: Partial cloverleaf interchange layout (four-quadrant Type A) ............ 499
Figure 12-28: Partial cloverleaf interchange layout (four quadrants Type B) .......... 500
Figure 12-29: Trumpet interchange layout .................................................................... 503
Figure 12-30: Trumpet interchange layout (Type A) ..................................................... 504
Figure 12-31: Trumpet interchange layout (Type B) ..................................................... 505
Page xxii
Figure 12-32: Directional interchanges ......................................................................... 507
Figure 12-33: Directional interchange with semi direct connections .......................... 508
Figure 12-34: Directional interchange (Google Earth) .................................................. 509
Figure 12-35: Directional interchange with semi direct connections (Google Earth). 509
Figure 12-36: Rotary (roundabout) interchange ........................................................... 510
Figure 12-37: Two-level turbine interchange ................................................................. 511
Figure 12-38: Three-level turbine interchange .............................................................. 512
Figure 12-39: Stack interchange .................................................................................... 512
Figure 12-40: Two-level clover stack interchange ........................................................ 513
Figure 12-41: Three-level clover stack interchange ...................................................... 514
Figure 12-42: Y interchange ........................................................................................... 514
Figure 12-43: T-interchange ........................................................................................... 515
Figure 12-44: Three level diamond/volleyball interchange .......................................... 515
Figure 12-45: Basketweave interchange ....................................................................... 516
Figure 12-46: Ramp types (1) ......................................................................................... 518
Figure 12-47: Separation between C-D roadway and mainline .................................... 521
Figure 12-48: Typical ramp cross sections ................................................................... 525
Figure 12-49: Curve types on exit ramps (1) ................................................................. 529
Figure 12-50: Exit ramp terminal (1) .............................................................................. 532
Figure 12-51: Two-lane exit ramp terminal (1) ............................................................... 533
Figure 12-52: Entrance ramp terminal (1) ...................................................................... 538
Figure 12-53: Two-lane entrance ramp terminal (1) ...................................................... 539
Figure 12-54: Merge and diverge influence areas (5) ................................................... 543
Figure 12-55: Crossroad designs to discourage wrong-way entry (two-lane) (1) ....... 546
Figure 12-56: Crossroad designs to discourage wrong-way entry (divided) (1)......... 547
Figure 12-57: Major diverges .......................................................................................... 551
Figure 12-58: Major converges ...................................................................................... 552
Figure 13-1: Pedestrian Realm (4) .................................................................................. 557
Figure 13-2: Mid-block crossing (4) ............................................................................... 560
Figure 13-3: Typical crosswalk elements (4) ................................................................. 563
Figure 13-4: Bus stops at mid-block crossing (1+1 street) (69) ................................... 567
Figure 13-5: Bus stop/lay-by after mid-block crossing (divided street) (69) ............... 567
Figure 13-6: Bus stop/lay-by before mid-block crossing (divided street) (69) ............ 568
Figure 13-7: Bus stop after mid-block crossing (divided street) (69) .......................... 568
Figure 13-8: Cycle Facilities (4) ...................................................................................... 569
Figure 13-9: Shared waiting space for cyclists and pedestrians at intersection (4) .. 570
Figure 13-10: Cross section of two-way shared use path on separated right-of-way (42) ......................................................................................................... 574
Figure 14-1: Moving vehicle to safely cross or stop at railroad crossing (1) .............. 578
Page xxiii
Figure 14-2: Departure of vehicle from stopped position to cross railroad track (1) . 580
Figure 14-3: Railroad-road grade crossings ................................................................. 581
Figure 16-1: The visual environment ............................................................................. 598
Figure 16-2: Roadway decisions with aesthetic implications ...................................... 599
Figure 16-3: Rest area ..................................................................................................... 611
Figure 16-4: Evaluation criteria for site selection, layout, and design of freeway rest areas ...................................................................................................... 613
Figure 16-5: Typical rest area design layout ................................................................. 615
Figure 16-6: Typical rest area design layout ................................................................. 616