National Academies Press: OpenBook

Highway and Street Design Vehicles: An Update (2023)

Chapter: Chapter 7 - Development of Design Guidance for the Application of Updated Design Vehicles

« Previous: Chapter 6 - Turning Performance of Updated Design Vehicles
Page 114
Suggested Citation:"Chapter 7 - Development of Design Guidance for the Application of Updated Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Page 114
Page 115
Suggested Citation:"Chapter 7 - Development of Design Guidance for the Application of Updated Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Page 115
Page 116
Suggested Citation:"Chapter 7 - Development of Design Guidance for the Application of Updated Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Page 116

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114 7.1 Proposed Revisions to the AASHTO Green Book This chapter documents the development of design guidance for the application of the updated design vehicles presented in this report. The recommended changes in design guidance are described in this chapter and are suggested as revisions to the Green Book. Revisions to the Green Book text have been made only in response to the design vehicle updates resulting from this research. These recommended changes will be provided for consideration by AASHTO for inclusion in the next revision of the Green Book. A broader effort to update the Green Book is currently underway in NCHRP Project 07-29. 7.1.1 Revisions to Green Book Section 2.8.1 (Design Vehicles: General Characteristics) Green Book Section 2.8.1 has been updated to incorporate one new design vehicle (a pickup truck, designated as the PU design vehicle) and revised dimensions (and, in some cases, revised names) for the 20 existing design vehicles. The symbols for many design vehicles have been revised to reflect the changes in the design vehicle names or dimensions. These changes are based on the recommendations presented in Chapter 5. The revised Green Book text incorporates a revised table of design vehicle dimensions based on Table 37 in Section 5.13. The changes in design vehicle names and symbols have been implemented throughout the updated Green Book text. 7.1.2 Revisions to Green Book Section 2.8.2 (Design Vehicles: Minimum Turning Paths of Design Vehicles) Green Book Section 2.8.2 has been updated to incorporate the changes in minimum turning paths resulting from the changes in design vehicle dimensions. In particular, the revisions in turning radii shown in Table 38 have been implemented in the corresponding tables in the Green Book, and the revised turning path plots shown in Figures 56 through 76 have been incor- porated in the corresponding figures in the Green Book. 7.1.3 New Green Book Section on Selection of Appropriate Design Vehicles for a Specific Roadway or Intersection A new subsection has been added to Green Book Section 2.8 on design vehicles that explains the process of selecting an appropriate design vehicle (or vehicles) for a specific roadway or intersection. The subsection addresses situations where multiple design vehicles may be appro- priate along the same project or corridor. It describes situations where a roadway is designed to accommodate one particular design vehicle without encroachment on adjacent lanes but where C H A P T E R 7 Development of Design Guidance for the Application of Updated Design Vehicles

Development of Design Guidance for the Application of Updated Design Vehicles 115 a larger design vehicle (designated as a check vehicle) may be accommodated with encroach- ment on adjacent lanes. The latter approach is consistent with recent practices of some agencies (City of Portland 2008). 7.1.4 New Green Book Section on Application of Selected Design Vehicles in Development of Roadway and Intersection Geometrics A new subsection has been added to Green Book Section 2.8 on design vehicles that explains the process of using the selected design vehicle(s) in the design of a roadway or intersection. 7.1.5 Revisions to Green Book Section 3.3.9 (Horizontal Alignment: Offtracking) Green Book Section 3.3.9 has been revised to incorporate new figures that show, for specific design vehicles, the swept path width defined by the vehicle tires and the front overhang of the vehicle as the vehicle traverses a curve of a specified radius. 7.1.6 Revisions to Green Book Section 3.3.10 (Horizontal Alignment: Traveled Way Widening on Horizontal Curves) Green Book Section 3.3.10 has been revised to update the tables that show the appropriate amount of traveled way widening to accommodate specific design vehicles on horizontal curves of specific radii. 7.1.7 Revisions to Green Book Section 3.3.11 (Horizontal Alignment: Widths for Turning Roadways at Intersections) Green Book Section 3.3.11 has been revised to update the tables that show widths for turning roadways at intersections to accommodate specific design vehicles on horizontal curves of specific radii. 7.1.8 Revisions to Green Book Section 4.15.12 (Roadside Control: Driveways) Green Book Section 4.15.12 incorporates an expanded discussion on the design of driveway alignment and profile to reduce the potential for vehicle undercarriages to come into contact with the roadway surface. 7.1.9 Revisions to Green Book Section 4.17.1 (Pedestrian Facilities: Sidewalks) Green Book Section 4.17.1 includes additional emphasis on the desirability of separating truck and pedestrian movements in space and in time. 7.1.10 Revisions to Green Book Section 4.18 (Bicycle Facilities) The discussion in Green Book Section 4.18 has been expanded to identify specific bicycle facility types that provide separation between bicyclists and motor vehicles. It should be noted that AASHTO is currently revising its bicycle guide. Additional material from the revised bicycle guide will likely be included in the Green Book revisions to be made in NCHRP Project 07-29.

116 Highway and Street Design Vehicles: An Update 7.1.11 Revisions to Green Book Section 4.19 (Transit Facilities) An explicit reference to the six bus design vehicles has been added in Green Book Section 4.19. 7.1.12 Revisions to Green Book Section 9.6.1 (Turning Roadways and Channelization: Turning Roadways) The discussion in Green Book Section 9.6.1 of the choice of curb radii and the effect of that choice on pedestrian crossing distance has been expanded. 7.1.13 Revisions to Green Book Section 9.7.3.6 (Auxiliary Lanes: Double and Triple Left-Turn Lanes) The tables of swept path widths in left turns for specific design vehicle types and specific turning radii have been updated in Green Book Section 9.7.3.6. This section has also been expanded to discuss typical actions by drivers of large vehicles at double and triple left-turn lanes and the possible accommodation of encroachment by larger vehicles on adjacent turning paths. 7.1.14 Revisions to Green Book Section 9.9.5 (Indirect Left Turns and U-Turns: Location and Design of U-Turn Median Openings) In Green Book Section 9.95, the table of minimum median widths to accommodate specific U-turn maneuvers for specific design vehicles on divided roadways has been updated to reflect the changes in design vehicle dimensions and turning performance. 7.1.15 Revisions to Green Book Section 9.10.2.4 (Roundabouts: Design Vehicle) Green Book Section 9.10.2.4 has been updated to explicitly mention the use of mountable aprons around the center island of a roundabout to better accommodate larger design vehicles. 7.1.16 Revisions to Green Book Section 9.12 (Railroad-Highway Grade Crossings) Green Book Section 9.12 has been revised to refer to the analysis procedure to accommodate vehicles with low ground clearance at driveways in Green Book Section 4.15.12, which is also applicable to railroad-highway grade crossings. The sight distance tables in Section 9.12 have also been revised to reflect the replacement of the WB-67 design vehicle by the slightly longer WB-69 design vehicle.

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Approximately 55 percent of the passenger vehicles registered in the United States are light trucks, such as sport utility vehicles, vans, minivans, and pickup trucks. Conventional automobiles, such as sedans and coupes, make up the rest of passenger vehicles.

NCHRP Research Report 1061: Highway and Street Design Vehicles: An Update, from TRB's National Cooperative Highway Research Program, proposes revisions to the dimensions of 16 of the 20 design vehicles used in the 2018 edition of AASHTO’s A Policy on Geometric Design of Highways and Streets, commonly known as the Green Book.

Supplemental to the report is a spreadsheet tool.

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