A Policy on Geometric Design Of Highways and Streets

ighway engineers, as designers, strive to meet the needs of highway users while maintaining the integrity of the environment. unique combinations of design controls and constraints that are often conflicting call for unique design solutions

HAMMAM Mohammed 4 years ago 0 73

Foreword

Highway engineers, as designers, strive to meet the needs of highway users while maintaining the integrity of the environment. unique combinations of design controls and constraints that are often conflicting call for unique design solutions. A Policy on Geometric Design of Highways and Streets provides guidance based on established practices that are supplemented by recent research. This document is also intended as a comprehensive reference manual to assist in administrative, planning, and educational efforts pertaining to design formulation.

Design values are presented in this document in both metric and u.S. customary units and were developed independently within each system. The relationship between the metric and u.S. customary values is neither an exact (soft) conversion nor a completely rationalized (hard) conversion; and the use of brackets around u.S. Customary values does not indicate as in some AASHTO publications that these are soft conversions. The metric values are those that would have been used had the policy been presented exclusively in metric units; the u.S. customary values are those that would have been used if the policy had been presented exclusively in u.S. customary units. Therefore, the user is advised to work entirely in one system and not attempt to convert directly between the two.

The fact that new design values are presented herein does not imply that existing streets and highways are unsafe, nor does it mandate the initiation of improvement projects. This publication is not intended as a policy for resurfacing, restoration, or rehabilitation (3r) projects. For projects of this type, where major revisions to horizontal or vertical curvature are not necessary or practical, existing design values may be retained. Specific site investigations and crash history analyses often indicate that the existing design features are performing in a satisfactory manner. The cost of full reconstruction for these facilities, particularly where major realignment is not needed, will often not be justified. resurfacing, restoration, and rehabilitation projects enable highway agencies to improve highway safety by selectively upgrading exising highway and roadside features without the cost of full reconstruction. When designing 3r projects, the designer should refer to TRB Special Report 214, Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation, and related publications for guidance.

The intent of this policy is to provide guidance to the designer by referencing a recommended range of values for critical dimensions. good highway design involves balancing safety, mobility, and preservation of scenic, aesthetic, historic, cultural, and environmental resources. This policy is therefore not intended to be a detailed design manual that could supersede the need for the application of sound principles by the knowledgeable design professional. Sufficient flexibility is permitted to encourage independent designs tailored to particular situations. Minimum values are either given or implied by the lower value in a given range of values. The larger values within the ranges may be used where social, economic, an environmental impacts are not critical. Engineering judgment is exercised by highway agencies to select
appropriate design values.

The highway, vehicle, and individual users are all integral parts of transportation safety and efficiency.

While this document primarily addresses geometric design issues, a properly equipped and maintained vehicle and reasonable and prudent performance by the user are also needed for safe and efficient operation of the transportation facility.

Emphasis is placed on the joint use of transportation corridors by pedestrians, cyclists, and public transit vehicles. Designers should recognize the implications of sharing transportation corridors and are encouraged to consider not only vehicular movement, but also movement of people, distribution of goods, and provision of essential services. A more comprehensive transportation program is thereby emphasized.

Cost-effective design is also emphasized. The traditional procedure of comparing highway-user benefits with costs has been expanded to reflect the needs of non-users and the environment. Although adding complexity to the analysis, this broader approach also takes into account both the need for a given project and the relative priorities among various projects. The results of this approach may need to be modified to meet the needs-versus-funds challenges that highway administrators face. The goal of cost-effective design is not merely to give priority to the most beneficial individual projects but to provide the most benefits to the highway system of which each project is a part.

Most of the technical material that follows is detailed or descriptive design information. Design guidelines are included for freeways, arterials, collectors, and local roads, in both urban and rural locations, paralleling the functional classification used in highway planning. The book is organized into functional chapters to stress the relationship between highway design and highway function. An explanation of functional classification is included in Chapter 1.

These geometric design guidelines are intended to provide operational efficiency, comfort, safety, and convenience for the motorist. The design concepts presented herein were also developed with consideration for environmental quality. The effects of the various environmental impacts can and should be mitigated by thoughtful design processes. This principle, coupled with that of aesthetic consistency with the surrounding terrain and urban setting, is intended to produce highways that are safe and efficient for users, acceptable to non-users, and in harmony with the environment.

This publication supersedes the 2004 AASHTO publication of the same name. Because the concepts presented cannot be completely covered in this one document, references to additional literature are given at the end of each chapter. These references include works that were cited or consulted in the development of the chapter or are of interest to the discussion of the subject matter therein. Of these documents, only those balloted and published by AASHTO represent AASHTO policy.

1-Highway Functions

1.1 SYSTEMS AND CLASSIFICATIONS

The classification of highways into different operational systems, functional classes, or geometric types is needed for communication among engineers, administrators, and the general public.

Various classification schemes have been applied for distinct purposes in different rural and urban regions. Classification of highways by design types based on the major geometric features (e.g., freeways, conventional streets, and highways) is the most helpful approach for highway location and design procedures. Classification by route numbering (e.g., U.S., State, and County) is the most helpful approach for traffic operations. Administrative classification (e.g., National Highway System or Non-National Highway System) is used to denote the levels of government responsible for and the method of financing highway facilities. Functional classification, the grouping of highways by the character of service they provide, was developed for transportation planning purposes. Comprehensive transportation planning, which is an integral part of total economic and social development, uses functional classification as an important planning tool.

The emergence of functional classification as the predominant method of grouping highways is consistent with the policies contained in this publication.

1.2 THE CONCEPT OF FUNCTIONAL CLASSIFICATION

This section introduces the basic concepts needed for understanding the functional classification of highway facilities and systems.

1.2.1 Hierarchies of Movements and Components

While the accommodation of bicyclists, pedestrians, and transit users is an important consideration in the planning and design of highways and streets, the functional classification of a highway or street is primarily based on motor vehicle travel characteristics and the degree of access provided to adjacent properties. Motor vehicle travel involves a series of distinct travel movements. The six recognizable stages in most trips include main movement, transition, distribution,

collection, access, and termination. For example, Figure 1-1 shows a hypothetical highway trip using a freeway, where the main movement of vehicles is uninterrupted, high-speed flow. When approaching destinations from the freeway, vehicles reduce speed on freeway ramps, which act as transition roadways. The vehicles then enter moderate-speed arterials (distributor facilities)

1-2 A Policy on Geometric Design of Highways and Streets

that bring them nearer to the vicinity of their destination neighborhoods. They next enter collector roads that penetrate neighborhoods. The vehicles finally enter local access roads that provide direct approaches to individual residences or other terminations. At their destinations, the vehicles are parked at an appropriate terminal facility.

Each of the six stages of this hypothetical trip is handled by a separate facility designed specifically for its function. Because the movement hierarchy is based on the total amount of traffic volume, freeway trave is generally the highest level in the movement hierarchy, below that is distributor arterial travel, and lowest in the movement hierarchy is travel on collectors and local access routes.

Although many trips can be subdivided into all of the six recognizable stages, intermediate facilities are not always needed. The complete hierarchy of circulation facilities most closely applies to conditions of low-lowdensity suburban development, where traffic flows are cumulative on successive elements of the system. However, travelers sometimes follow a reduced number of components in the chain. For instance, a large single traffic generator may fill one or more lanes of a freeway during certain periods. In this situation, it is expedient to lead traffic directly onto a freeway ramp without using arterial facilities that would unnecessarily mix already-concentrated traffic flows with additional vehicles. This absence of intermediate facilities does not eliminate the functional need for the remaining levels of the flow hierarchy or the functional design components, although it may change their physical features. The order of movement is still identifiable.

A prominent cause of highway obsolescence is the failure of a design to recognize and accommodate each of the different trip levels of the movement hierarchy. Conflicts and congestion occur at interfaces between public highways and private traffic-generating facilities when the functional transitions are inadequate. Examples are commercial driveways that connect directly from a relatively high-speed arterial to a parking aisle without intermediate provisions for transition deceleration and arterial distribution or, more seriously, freeway ramps that connect directly to or from large traffic generators such as major shopping centers.

Inadequate capacity of the distributor arterial to serve traffic demands or internal circulation deficiencies within a destination facility or network may lead to traffic backing up onto the freeway. Successful internal design that provides facilities to accommodate all the intermediate functions between the high-speed freeway and the terminal parking facility will alleviate such a situation.

In the case of a freeway connecting directly to a large traffic generator, deceleration from rapid movement on the freeway occurs on the exit ramp. Distribution to various parking areas is then accomplished by primary distribution-type roads or lanes within the parking facility. These roads or lanes supplant the distributor arterial function. Collector-type roads or lanes within the parking facility may then deliver segments of the entering flow to the parking bays. The parking aisle, in leading to individual parking space terminals, then becomes the equivalent of an access street. Thus, the principal functions within the hierarchical movement system are recognizable. In addition, each functional category also is related to a range of vehicle speeds.

The same principles of design are also relevant to terminal facilities that adjoin distributor arterials or collectors. The functional design of the facility includes each movement stage, with internal circulation in the terminal design to accommodate the order of movement. The need to design for all stages of the movement hierarchy varies with the size of the traffic generator. For relatively small generators, two or more stages may be accommodated on the same internal facility. For larger traffic generators, each movement stage should have a separate functional facility.

The number of design components needed can be determined by comparing the customary volumes of traffic handled by public streets of different functional categories. The volume range on private internal facilities can be related to the comparable range on public streets. These volumes may not be directly comparable, inasmuch as the physical space available within a private facility is smaller and the operational criteria are appropriately quite different. However, the same principles of flow specialization and movement hierarchy can be applied.

Some further examples may demonstrate how the principles of movement hierarchy are related to a logical system of classifying traffic generation intensity. At the highest practical level of traffic generation, a single generator fills an entire freeway and, for this condition, intermediate public streets cannot be inserted between the generator and the freeway; consequently, the various movement stages should be accommodated internally with appropriate design features. At the next level of traffic generation, a single traffic generator could fill a single freeway lane. It is then appropriate to construct a freeway ramp for the exclusive use of the generator without intervening public streets. At still smaller volumes, it becomes desirable to combine the traffic from several generators before the flow arrives at a freeway entrance ramp.

The road performing this function then becomes a collector facility to accumulate these small flows until reaching a traffic volume that will fill the freeway ramp.

Similar principles can be applied at the distributor arterial level of service. If a given traffic generator is of sufficient size, an exclusive intersection driveway for that generator is justified. In other cases, an intermediate collector street should combine smaller traffic flows until they reach a volume that warrants an intersection along the distributor. The same theory can be applied with regard to the criteria for direct access to the collector street. A moderately sized traffic generator usually warrants a direct connection to the collector without an intermediate access street; however, in a district of single-family residences, a local access street should assemble the traffic from a group of residences and lead it into a collector street at a single point of access. In practice, direct access to arterials and collectors should be provided from commercial and residential properties, particularly in established neighborhoods.

In short, each element of the functional hierarchy can serve as a collecting facility for the next higher element, but an element should be present only if intermediate collection is needed to satisfy the spacing needs and traffic volume demands of the next higher facility. By estimating or forecasting the spacing needs and traffic volume demands for a system element, it is possible to identify which cases should use the full system and which cases may bypass intermediate elements.

CHAPTER 1 HIGHWAY FUNCTIONS

1.1 SYSTEMS AND CLASSIFICATIONS
1.2 THE CONCEPT OF FUNCTIONAL CLASSIFICATION
1.2.1 Hierarchies of Movements and Components
1.2.2 Functional Relationships
1.2.3 Access Needs and Controls
1.3 FUNCTIONAL SYSTEM CHARACTERISTICS
1.3.1 Definitions of Urban and Rural Areas
1.3.2 Functional Categories
1.3.3 Functional Systems for Rural Areas
1.3.4 Functional Highway Systems in Urbanized Areas
1.3.5 Functional Classification as a Design Type
1.4 REFERENCES

CHAPTER 2 DESIGN CONTROLS AND CRITERIA

2.1 DESIGN VEHICLES
2.1.1 General Characteristics
2.1.2 Minimum Turning Paths of Design Vehicles
2.1.3 Vehicle Performance
2.1.4 Vehicular Pollution
2.2 DRIVER PERFORMANCE AND HUMAN FACTORS
2.2.1 Introduction
2.2.2 Older Drivers and Older Pedestrians
2.2.3 The Driving Task
2.2.4 The Guidance Task
2.2.5 The Information System
2.2.6 Information Handling
2.2.7 Driver Error
2.2.8 Speed and Design
2.2.9 Design Assessment
2.3 TRAFFIC CHARACTERISTICS
2.3.1 General Considerations
2.3.2 Volume
2.3.3 Directional Distribution
2.3.4 Composition of Traffic
2.3.5 Projection of Future Traffic Demands
2.3.6 Speed 2.3.7 Traffic Flow Relationships
2.4 HIGHWAY CAPACITY
2.4.1 General Characteristics
2.4.2 Application
2.4.3 Capacity as a Design Control
2.4.4 Factors Other Than Traffic Volume That Affect Operating Conditions
2.4.5 Levels of Service
2.4.6 Design Service Flow Rates
2.5 ACCESS CONTROL AND ACCESS MANAGEMENT
2.5.1 General Conditions
2.5.2 Basic Principles of Access Management
2.5.3 Access Classifications
2.5.4 Methods of Controlling Access
2.5.5 Benefits of Controlling Access
2.6 THE PEDESTRIAN
2.6.1 General Considerations
2.6.2 General Characteristics
2.6.3 Walking Speeds
2.6.4 Walkway Level of Service
2.6.5 Intersections
2.6.6 Reducing Pedestrian-Vehicular Conflicts
2.6.7 Characteristics of Persons with Disabilities
2.7 BICYCLE FACILITIES
2.8 SAFETY
2.8.1 Key Factors Related to Traffic Crashes
2.8.2 Key Safety Resources
2.8.3 Safety Improvement Programs
2.8.4 Project Development Process
2.9 ENVIRONMENT
2.10 ECONOMIC ANALYSIS
2.11 REFERENCES

CHAPTER 3 ELEMENTS OF DESIGN

3.1 INTRODUCTION
3.2 SIGHT DISTANCE
3.2.1 General Considerations
3.2.2 Stopping Sight Distance
3.2.3 Decision Sight Distance
3.2.4 Passing Sight Distance for Two-Lane Highways
3.2.5 Sight Distance for Multilane Highways
3.2.6 Criteria for Measuring Sight Distance
3.3 HORIZONTAL ALIGNMENT
3.3.1 Theoretical Considerations
3.3.2 General Considerations
3.3.3 Design Considerations
3.3.4 Design for Rural Highways, Urban Freeways, and High-Speed Urban Streets
3.3.5 Design Superelevation Tables
3.3.6 Design for Low-Speed Urban Streets
3.3.7 Turning Roadways
3.3.8 Transition Design Controls
3.3.9 Offtracking
3.3.10 Traveled-Way Widening on Horizontal Curves
3.3.11 Widths for Turning Roadways at Intersections
3.3.12 Sight Distance on Horizontal Curves
3.3.13 General Controls for Horizontal Alignment
3.4 VERTICAL ALIGNMENT
3.4.1 Terrain
3.4.2 Grades
3.4.3 Climbing Lanes
3.4.4 Methods for Increasing Passing Opportunities on Two-Lane Roads
3.4.5 Emergency Escape Ramps
3.4.6 Vertical Curves
3.5 COMBINATIONS OF HORIZONTAL AND VERTICAL ALIGNMENT
3.5.1 General Considerations
3.5.2 General Design Controls
3.5.3 Alignment Coordination in Design
3.6 OTHER FEATURES AFFECTING GEOMETRIC DESIGN
3.6.1 Erosion Control and Landscape Development
3.6.2 Rest Areas, Information Centers, and Scenic Overlooks
3.6.3 Lighting
3.6.4 Utilities
3.6.5 Traffic Control Devices
3.6.6 Traffic Management Plans for Construction
3.7 REFERENCES

CHAPTER 4 CROSSͳSECTION ELEMENTS

5.1 INTRODUCTION
5.2 LOCAL RURAL ROADS
5.2.1 General Design Considerations
5.2.2 Cross-Sectional Elements
5.2.3 Structures
5.2.4 Roadside Design
5.2.5 Intersection Design
5.2.6 Railroad-Highway Grade Crossings
5.2.7 Traffic Control Devices
5.2.8 Drainage
5.2.9 Erosion Control and Landscaping
5.3 LOCAL URBAN STREETS
5.3.1 General Design Considerations
5.3.2 Cross-Sectional Elements
5.3.3 Structures
5.3.4 Roadside Design
5.3.5 Intersection Design
5.3.6 Railroad-Highway Grade Crossings
5.3.7 Traffic Control Devices
5.3.8 Roadway Lighting
5.3.9 Drainage
5.3.10 Erosion Control
5.3.11 Landscaping
5.4 SPECIAL-PURPOSE ROADS
5.4.1 Introduction
5.4.2 Recreational Roads
5.4.3 Resource Recovery Roads
5.5 VERY LOW-VOLUME LOCAL ROADS (ADT ≤ 400)
5.6 REFERENCES

CHAPTER 6 COLLECTOR ROADS AND STREETS

6.1 INTRODUCTION
6.2 RURAL COLLECTORS
6.2.1 General Design Considerations
6.2.2 Cross-Sectional Elements
6.2.3 Structures
6.2.4 Roadside Design
6.2.5 Intersection Design
6.2.6 Railroad-Highway Grade Crossings
6.2.7 Traffic Control Devices
6.2.8 Drainage
6.2.9 Erosion Control and Landscaping
6.3 URBAN COLLECTORS
6.3.1 General Design Considerations
6.3.2 Cross-Sectional Elements
6.3.3 Structures
6.3.4 Roadside Design
6.3.5 Intersection Design
6.3.6 Railroad-Highway Grade Crossings
6.3.7 Traffic Control Devices
6.3.8 Roadway Lighting
6.3.9 Drainage
6.3.10 Erosion Control
6.3.11 Landscaping
6.4 REFERENCES

CHAPTER 7 RURAL AND URBAN ARTERIALS

7.1 INTRODUCTION
7.2 RURAL ARTERIALS
7.2.1 General Characteristics
7.2.2 General Design Considerations
7.2.3 Cross-Sectional Elements
7.2.4 Roadside Design
7.2.5 Structures
7.2.6 Traffic Control Devices
7.2.7 Erosion Control
7.2.8 Provision for Passing
7.2.9 Ultimate Development of Multilane Divided Arterials
7.2.10 Multilane Undivided Arterials
7.2.11 Divided Arterials
7.2.12 Intersections
7.2.13 Access Management
7.2.14 Bicycle and Pedestrian Facilities
7.2.15 Bus Turnouts
7.2.16 Railroad-Highway Grade Crossings
7.2.17 Rest Areas
7.3 URBAN ARTERIALS
7.3.1 General Characteristics
7.3.2 General Design Considerations
7.3.3 Cross-Sectional Elements
7.3.4 Roadside Design
7.3.5 Structures
7.3.6 Traffic Barriers
7.3.7 Railroad-Highway Grade Crossings
7.3.8 Access Management
7.3.9 Bicycle and Pedestrian Facilities
7.3.10 Provision for Utilities
7.3.11 Intersection Design
7.3.12 Operational Control and Regulations
7.3.13 Directional Lane Usage
7.3.14 Frontage Roads and Outer Separations
7.3.15 Grade Separations and Interchanges
7.3.16 Erosion Control
7.3.17 Lighting
7.3.18 Public Transit Facilities
7.4 REFERENCES

CHAPTER 8 FREEWAYS

8.1 INTRODUCTION
8.2 GENERAL DESIGN CONSIDERATIONS
8.2.1 Design Speed
8.2.2 Design Traffic Volumes
8.2.3 Levels of Service
8.2.4 Traveled Way and Shoulders
8.2.5 Curbs
8.2.6 Superelevation
8.2.7 Grades .
8.2.8 Structures
8.2.9 Vertical Clearance
8.2.10 Roadside Design
8.2.11 Ramps and Terminals
8.2.12 Outer Separations, Borders, and Frontage Roads
8.3 RURAL FREEWAYS
8.3.1 Alignment and Profile
8.3.2 Medians
8.3.3 Sideslopes
8.3.4 Frontage Roads
8.4 URBAN FREEWAYS
8.4.1 General Design Characteristics
8.4.2 Medians
8.4.3 Depressed Freeways
8.4.4 Elevated Freeways
8.4.5 Ground-Level Freeways
8.4.6 Combination-Type Freeways
8.4.7 Special Freeway Designs
8.4.8 Accommodation of Managed Lanes and Transit Facilities
8.5 REFERENCES

CHAPTER 9 INTERSECTIONS

9.1 INTRODUCTION
9.2 GENERAL DESIGN CONSIDERATIONS AND OBJECTIVES
9.2.1 Characteristics of Intersections
9.2.2 Intersection Functional Area
9.2.3 Design Objectives
9.2.4 Design Considerations for Intersection User Groups
9.2.5 Intersection Capacity
9.2.6 Intersection Design Elements
9.3 TYPES AND EXAMPLES OF INTERSECTIONS
9.3.1 Three-Leg Intersections
9.3.2 Four-Leg Intersections
9.3.3 Multileg Intersections
9.3.4 Roundabouts
9.4 ALIGNMENT AND PROFILE
9.4.1 General Considerations
9.4.2 Alignment
9.4.3 Profile
9.5 INTERSECTION SIGHT DISTANCE
9.5.1 General Considerations
9.5.2 Sight Triangles
9.5.3 Intersection Control
9.5.4 Effect of Skew
9.6 TURNING ROADWAYS AND CHANNELIZATION
9.6.1 Types of Turning Roadways
9.6.2 Channelization
9.6.3 Islands
9.6.4 Free-Flow Turning Roadways at Intersections
9.6.5 Turning Roadways with Corner Islands
9.6.6 Superelevation for Turning Roadways at Intersections
9.6.7 Stopping Sight Distance at Intersections for Turning Roadways
9.7 AUXILIARY LANES
9.7.1 General Design Considerations
9.7.2 Deceleration Lanes
9.7.3 Design Treatments for Left-Turn Maneuvers
9.8 MEDIAN OPENINGS
9.8.1 General Design Considerations
9.8.2 Control Radii for Minimum Turning Paths
9.8.3 Minimum Length of Median Opening
9.8.4 Median Openings Based on Control Radii for Design Vehicles
9.8.5 Effect of Skew
9.8.6 Above-Minimum Designs for Direct Left Turns
9.9 INDIRECT LEFT TURNS AND U-TURNS
9.9.1 General Design Considerations
9.9.2 Intersections with Jughandle or Loop Roadways
9.9.3 Displaced Left-Turn Intersections
9.9.4 Wide Medians with U-Turn Crossover Roadways
9.9.5 Location and Design of U-Turn Median Openings
9.10 ROUNDABOUT DESIGN
9.10.1 Geometric Elements of Roundabouts
9.10.2 Fundamental Principles
9.11. OTHER INTERSECTION DESIGN CONSIDERATIONS
9.11.1 Intersection Design Elements with Frontage Roads
9.11.2 Traffic Control Devices
9.11.3 Bicycles
9.11.4 Pedestrians
9.11.5 Lighting
9.11.6 Driveways
9.11.7 Midblock Left Turns on Streets with Flush Medians
9.12 RAILROAD-HIGHWAY GRADE CROSSINGS
9.12.1 Horizontal Alignment
9.12.2 Vertical Alignment
9.12.3 Crossing Design
9.12.4 Sight Distance
9.13 REFERENCES

ChAPTER 10 GRADE SEPARATIOnS AND InTERChAngES

10.1 INTRODUCTION AND GENERAL TYPES OF INTERCHANGES
10.2 WARRANTS FOR INTERCHANGES AND GRADE SEPARATIONS
10.3 ADAPTABILITY OF HIGHWAY GRADE SEPARATIONS AND INTERCHANGES
10.3.1 Traffic and Operation
10.3.2 Site Conditions
10.3.3 Type of Highway and Intersecting Facility
10.4 ACCESS SEPARATIONS AND CONTROL ON THE CROSSROAD AT INTERCHANGES
10.5 SAFETY
10.6 STAGE DEVELOPMENT
10.7 ECONOMIC FACTORS
10.7.1 Initial Costs
10.7.2 Maintenance Costs
10.7.3 Vehicular Operating Costs
10.8 GRADE SEPARATION STRUCTURES
10.8.1 Introduction
10.8.2 Types of Separation Structures
10.8.3 Overpass versus Underpass Roadways
10.8.4 Underpass Roadways
10.8.5 Overpass Roadways
10.8.6 Longitudinal Distance to Attain Grade Separation
10.8.7 Grade Separations without Ramps
10.9 INTERCHANGES
10.9.1 General Considerations
10.9.2 Three-Leg Designs
10.9.3 Four-Leg Designs
10.9.4 Other Interchange Configurations
10.9.5 General Design Considerations
10.9.6 Ramps
10.9.7 Other Interchange Design Features
10.10 REFERENCES

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