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THE 2001 GREEN BOOK

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Chapter 5
Local Roads and Streets

• Exhibits updated to reflect changes in Chapter 3 and 9
• Superelevation
• Structures
• Clear zone
• Sight distance
• Parking lanes
• Intersections

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Note

AASHTO is currently evaluating alternative criteria for local and collector roads with volumes < 400 vehicles per day

Guidelines for Geometric Design of Very Low - Volume Local Roads (< 400 ADT) (Forthcoming)

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Exhibits

Four Exhibits revised to be consistent with Chapter 3 revisions:

• Exhibit 5 - 2 Stopping Sight Distance
• Exhibit 5 - 3 Passing Sight Distance
• Exhibit 5 - 13 Stopping Sight Distance Recreational Roads
• Exhibit 5 - 14 Passing Sight Distance Recreational Roads

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Miscellaneous

• Maximum superelevation allowed for rural roads changed from 10 % to 12 %
• Exhibit 5 - 6 Footnotes added for surfaced approaches and long bridges ( 30 m [ 100 ft ])
• Clear zone width now 2 - 3 m [ 7 - 10 ft ]
• Corner sight distance criteria deleted - See Chapter 9
• Parking lanes added

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Intersection Design

Intersection design section reworded

• Exhibit 5 - 10 added
• Discusses two distinct radii to consider
  • Effective turning radius
  • Curb return radius

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Chapter 6
Collector Roads and Streets

• Exhibits
• Design speed for horizontal clearance
• Medians
• Parking lanes

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Collector Exhibits

Two exhibits updated to be consistent with Chapter 3 revisions:

• Exhibit 6 - 2 Stopping Sight Distance
• Exhibit 6 - 3 Passing Sight Distance

Table for maximum grades in previous editions replaced by two exhibits:

• Exhibit 6 - 4 Maximum grades for rural
• Exhibit 6 - 8 Maximum grades for urban

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Miscellaneous

• Design speed revised to upper limit of 70 km/h [ 45 mph ] for low-speed design
  • Minimum clear zone of 3 m [ 10 ft ] on rural collectors
• Median discussion and widths on urban collectors modified slightly

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Parking Lanes

• Revisions:
  • Residential areas - 2.1 to 2.4 m [ 7 to 8 ft ] parking lane width
  • Commercial areas - 2.4 to 3.0 m [ 8 to 11 ft ] parking lane width
  • Industrial areas - 2.4 to 3.0 m [ 8 to 11 f t ] parking lane width

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Chapter 7
Rural and Urban Arterials

• Sight distance exhibit
• Widths
• Medians
• Curbs and shoulders
• Access management
• Turning radius for dual left turns

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Exhibits

• Exhibit 7 - 1 Sight distance values moved from Provisions for Passing to Sight Distance in the chapter
• Exhibit 7 - 3:
  • adjusted lane width from 6.6 m [ 22 ft ] to 7.2 m [ 24 ft ] for 80 km/h [ 50 mph ] and ADT of 1500 to 2000
  • column heading changed from DHV over 200 to ADT over 2000

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Widths

• A minimum of 0.6 m [2 ft ] paved shoulder width should be provided for pavement support, wide vehicles, collision avoidance and bicycles
• Section on Bridges to Remain added to provide minimum widths for existing bridges that will be retained

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Medians

• Advises against using 4 - lane undivided facilities
• Median discussion expanded and updated for both rural and urban
• Curb and Shoulders relocated to follow Lane Widths

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Access Management

Access Management replaces Access Control

• Refers to Chapter 2 discussion
• Discussion on left turns into and out of adjacent properties added

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Miscellaneous

• Pedestrian Facilities updated
  • Refers to Chapter 4
• Operation and Control Measures for Left - Turns
  • Desirable turning radius 27 m [ 90 ft ]

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Chapter 8
Freeways

• Updated to be consistent with other chapters
• Rural freeway discussion now precedes urban
• Allowance for height of resurfacing no longer specified
• Vertical clearance over railroads
  • 6.6 m [21.5 ft] minimum increased to 7.0 m [23 ft]

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Chapter 9
Intersections

Types
Functional area defined
Discussion of roundabouts
Turning roadways
Islands
Intersection sight distance
Offset left turn lanes

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Types

3 general types of intersections defined:

• At-grade
• Grade separations without ramps
• Interchanges

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Functional Area Defined

• Perception - reaction time
• Maneuver distance (braking & lane changing)
• Queue - storage distance (accommodate longest queue expected)

Defined by physical area

Defined by functional area

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Roundabouts

Yield at entry Deflection of entering traffic Discussion only FHWA-RD-00-067 Roundabouts: An Informational Guide

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Turning Roadways

• Discussion reorganized
• All exhibits updated to be consistent with Chapter 2 design vehicles
• Maximum superelevation rate increased to 12 % where climate is favorable

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Islands

• Minimum Design for Turning Roadways now part of General Characteristics
• Reversals in curvature for divisional islands reduced:
  • Minimum of 1165 m [ 3825 ft ] for rural areas
  • Minimum 620 m [ 2035 ft ] for speeds up to 70 km/h [ 45 mph ]
• Free - flow Turning Roadways replaces Application at Terminals

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Intersection Sight Distance

Six cases

• No control
• Stop control
• Yield control
• Signal control
• All-way stop control
• Left turn from major road

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Gap Acceptance
Sight Triangles

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Intersection Sight Distance

Speed	94 GB [90 GB]	2001 GB
	ISD	ISD
80 km/h [50 mph]	250 m [840 ft]	170 m [555 ft]

ISD = intersection sight distance for turning left from stop onto major highway

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Offset Left - Turn Lanes

Advantages: Better visibility Reduced conflict More vehicles served

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Miscellaneous

• Horizontal control see Chapter 3
• Deceleration length:
  • Discussion revised
  • Additional design speeds and values included
• Discussion on driveways expanded

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Chapter 10
Grade Separations and Interchanges

Access separations and control on crossroad at interchanges
Turning roadway widths
Single - point urban interchanges
Superelevation and cross slopes
Two lane entrance ramps

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Miscellaneous

• Recommends separation of bicycle/pedestrian movement from vehicle movement through interchanges
• Single Point Urban Interchange discussed as separate type
• Exhibit 10-67 made consistent with Exhibit 3-55

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Access Control at Interchanges

Minimizes spillback on ramp & crossroad
Distance for crossroad weaves
Distance for merging maneuvers
Provides storage for turning vehicles

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Miscellaneous

• Cautions against the use of minimum values for taper type entrances
• Exhibit 10-70 Acceleration lengths have been recomputed
• Adds a caution concerning volumes exceeding lane capacity on 2-lane ramps

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Technical Corrections

• Exhibit 3 - 55 and Exhibit 10 - 67 - In metric side, under Case I column, replace "with" with "no" so it is identical with US Customary.
• Exhibit 3 - 76 - Delete "and Sag" from title.
• Exhibit 5 - 11 - Replace "5.5" under residential in the metric side with "2.2".

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Technical Corrections

• Exhibit 10 - 60 is incorrect. It should be similar to Figure X-66 in 94 GB.
• Exhibit 10-71 - In the metric side, under the column All Speeds, in Acceleration Lanes, change the second occurrence of "3 to 4 % Downgrade" to "5 to 6 % Downgrade"

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Future Research

Truck impacts on criteria (underway)
Improved design for freeway speed change lanes (proposed)
Design criteria and warrants for right turn deceleration (proposed)
Auxiliary through lanes and lane drops (proposed)
Passing sight distance (proposed)

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