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Clear Zone Conflicts in AASHTO Publications

Clear Zone Conflicts in AASHTO Publications. Dick Albin Washington State Department of Transportation. Presented at the AASHTO Subcommittee on Design Meeting June 14, 2006 Orlando, Florida. Background. In 2001, WSDOT was asked to clarify our Clear Zone Policy

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Clear Zone Conflicts in AASHTO Publications

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  1. Clear Zone Conflicts in AASHTO Publications Dick Albin Washington State Department of Transportation Presented at the AASHTO Subcommittee on Design Meeting June 14, 2006 Orlando, Florida

  2. Background • In 2001, WSDOT was asked to clarify our Clear Zone Policy • In reviewing the AASHTO publications, many conflicts were identified • The AASHTO Technical Committee on Roadside Safety proposed an NCHRP 20-7 project to further identify conflicts

  3. Clear Zone is addressed in several different AASHTO publications • Roadside Design Guide • Green Book • Guidelines for Geometric Design of Very Low-Volume Local Roads • A Guide to Achieving Flexibility in Highway Design

  4. Examples - Definition • There are different terms that relate to the clear zone • Clear zone • Clear recovery area • Horizontal clearance • There are slight differences in the definitions for these between the Green Book and Roadside Design Guide

  5. Examples • Roadside Design Guide contains guidance based on speed, ADT (including <400) and side slope • Green Book refers to the RDG but also has guidance based on functional class “For rural collector roads with design speeds of 70 km/h [45 mph] or less, a minimum clear zone of 3 m [10 ft]… “

  6. Examples • The RDG guidance (Table 3.1) has an ADT Range for “Under 750” and suggests the Clear Zone ranges from 7’ to 26’ depending on speed • The Guide for Very Low Volume Roads (<400 ADT) indicates a clear zone of 6’ should be considered (no speed criteria)

  7. Examples – Horizontal Clearance • While there have been some attempts to distinguish between horizontal clearance and clear zone, Every section on horizontal clearance in the Green book discusses clear zone

  8. Examples – Operational • With the current language there continues to be confusion in the interpretation of the operational offset.

  9. Example - Luminaires Green Book Breakaway poles should not be used on streets in densely developed areas, particularly with sidewalks. Green Book Breakaway poles should not be used on streets in densely developed areas, particularly with sidewalks Roadside Design Guide As a general rule, breakaway supports should be used unless an engineering study indicates otherwise. However, concern for pedestrian involvement has led to the use of fixed supports in some urban areas. Examples of sites where breakaway supports may be imprudent are adjacent to bus shelters or in areas of extensive pedestrian concentrations.

  10. Background • NCHRP project 20-7 (171), Identification of Conflicts Related to Clear Zones within AASHTO Publications, was completed by Tim Neumann (CH2M Hill) in December 2004. • This report contained 15 recommendations

  11. Status • A Task Force comprised of members of the Technical Committees on Geometric Design and Roadside Safety was charged with addressing these recommendations Roadside Safety Rory Meza Texas DOT Rick Wilder New York DOT Mark Ayton Ontario Ministry of Trans. Dick Albin Washington DOT Steve Walker Alabama DOT Dick Powers FHWA Geometric Design Reza Amini Oklahoma DOT Rick Bruce Ohio DOT Philip J. Clark New York DOT Max Valerio New Mexico DOT Bill Prosser FHWA

  12. 20-7 Project Recommendations • AASHTO should clearly designate the Roadside Design Guide as the definitive publication for roadside issues. Task Force Agrees • One single definition for the term clear zone should be adopted Task Force is preparing a proposal for the definition

  13. 20-7 Project Recommendations • Need to Resolve and establish the technical basis for clear zone dimensions 2 NCHRP projects are on-going 17-11 – Determination of Safe / Cost Effective Roadside Slopes and Associated Clear Distances 16-04 – Design guidelines for Safe and Aesthetic Roadside treatments in Urban Areas

  14. 20-7 Project Recommendations • Need to clarify AASHTO intent on the use of clear zone dimensions Task Force agrees that clear zone dimensions are not precise and that they are a guide for selecting a clear zone for a project This intent will be addressed with the definitions.

  15. 20-7 Project Recommendations • Need to clarify AASHTO intent on the use of clear zone dimensions

  16. 20-7 Project Recommendations • Clarify how auxiliary lanes affect the clear zone. Task Force agrees that clarification is needed and will propose how these are treated This intent will be addressed with the definitions.

  17. 20-7 Project Recommendations • A major conflict concerns how/if functional classification factors into the clear zone selection Task Force proposes to move dimensional guidance from Green Book to the RDG. Currently functional class is not in the RDG. The results for the NCHRP projects will be used as the basis of the suggested dimensions.

  18. 20-7 Project Recommendations • Future editions of the GB and RDG should contain a single definition for auxiliary lanes. Task Force agrees • RDG figures for Clear zone should cover all ranges of Design Speeds The results for the NCHRP projects would be used as the basis of the suggested dimensions.

  19. 20-7 Project Recommendations • AASHTO needs to clarify the relationship between curbs and clear zone. Task Force agrees and will propose changes to the GB and RDG

  20. 20-7 Project Recommendations • The Green Book should clarify the differences between “Horizontal clearance,” “operational offset” and “clear zone” Task Force proposes to use the terms “Lateral Offset” rather than horizontal clearance and Operational offset and separate the discussions on these from the Clear zone discussion.

  21. 20-7 Project Recommendations • AASHTO needs to clearly address how roadside safety is addressed in low to moderate speed, urban highways. Task Force agrees. This is the intent of NCHRP project 16-04.

  22. 20-7 Project Recommendations • Clarify the definition of traveled way in regard to whether bike lanes are in or out. Task Force will propose that bike lanes not be consider part of the traveled way for clear zone purposes.

  23. 20-7 Project Recommendations • Clarify the need for barrier to separate a high speed highway from a shared use path that is within the clear zone. Task Force believes this is more of a barrier warrants issue and that the committee on Non Motorized Transportation should work with the Roadside Safety committee to resolve

  24. 20-7 Project Recommendations • Clarify where the clear zone is measured when shoulder driving is allowed. Task Force believes that shoulder driving is relatively rare and that when it is allowed, such as during peak hours, speeds are reduced. Proposed to maintain the clear zone from the edge of the normal through lanes

  25. 20-7 Project Recommendations • AASHTO should tie together the design information and processes related to the border area. In addressing the previous recommendations, we believe that the AASHTO guidance will be more coordinated.

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