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                        W-Beam Guardrail Repair: A Guide for Highway and Street Maintenance Personnel


            
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                APPENDIX D: CLEAR ZONE DESCRIPTION
APPENDIX D: CLEAR ZONE DESCRIPTION

The concept of clear zone is an approach to minimize the number and severity of crashes involving vehicles running off the road. Simply stated, it is a traversable area that starts at the edge of the traffic lane and extends laterally a sufficient distance to allow a driver to stop or return to the road before encountering a hazard or overturning. The traversable area would be considered safe, if there were no fixed objects, unless they are breakaway, and if the roadside geometry (either the fore slope, back slope, or ditch) was flat enough that a vehicle could safely traverse the area without tipping and rolling over. Roadside safety features include breakaway sign and light posts, and traversable drainage structures. Curbs are not considered a roadside safety feature since they can be easily mounted by errant vehicles; hence, their presence does not alter how clear zone is measured.

Clear Zone Illustration

A safe traversable slope can be either a recoverable slope or a non-recoverable slope with a clear run-out area at the bottom. A **recoverable slope** is a slope on which a motorist may, to a greater or lesser extent, retain or regain control of a vehicle and recover or stop. Slopes 1:4 (Vertical:Horizontal) or flatter are generally considered recoverable. A **non-recoverable, traversable slope** is a slope which is considered traversable but on which an errant vehicle will continue to the bottom. Embankment slopes from 1:3 and 1:4 may be considered traversable but non-recoverable if they are smooth and free of fixed objects. A **clear run-out area** is the flatter area at the toe of a non-recoverable slope available for safe use by an errant vehicle. Slopes steeper than 1:3 are not considered traversable and should not be found in the clear zone.

The objective of roadside safety is to provide and maintain as much clear zone as practical. The design clear zone is the minimum width to be provided on a project and is dependent upon speeds, the roadside geometry, and traffic volumes. Further details on clear zone can be found in the *Roadside Design Guide.*

[1] Design can be seen at ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/roadway/mbgtl205.pdf

[2] See Appendix D for description of clear zone.
      
  Book traversal links for APPENDIX D: CLEAR ZONE DESCRIPTION
      ‹ APPENDIX C: MAINTENANCE GUIDANCE
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                Book:W-Beam Guardrail Repair: A Guide for Highway and Street Maintenance Personnel
              I. INTRODUCTION: INTENT AND CONTENT
                II. IDENTIFY PROBLEMS AND PLAN APPROPRIATE ACTION
                III. REPAIR SEQUENCE GUIDANCE
                IV. REPAIR RECORD
                REFERENCES
                APPENDIX A: ESTIMATING RESOURCES FOR W-BEAM GUARDRAIL REPAIR
                APPENDIX B: VIRGINIA DOT REPAIR GUIDANCE
                APPENDIX C: MAINTENANCE GUIDANCE
                APPENDIX D: CLEAR ZONE DESCRIPTION U.S. DEPARTMENT OF TRANSPORTATION

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