Transcript 2006 Albin - AASHTO - Subcommittee on Design

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
• 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
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
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
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]… “
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)
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
Examples – Operational
• With the current language there continues
to be confusion in the interpretation of the
operational offset.
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.
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
Status
• A Task Force comprised of members of
the Technical Committees on Geometric
Design and Roadside Safety was charged
with addressing these recommendations
Geometric Design
Roadside Safety
Reza Amini
Rick Bruce
Philip J. Clark
Max Valerio
Bill Prosser
Rory Meza
Rick Wilder
Mark Ayton
Dick Albin
Steve Walker
Dick Powers
Oklahoma DOT
Ohio DOT
New York DOT
New Mexico DOT
FHWA
Texas DOT
New York DOT
Ontario Ministry of Trans.
Washington DOT
Alabama DOT
FHWA
20-7 Project Recommendations
1. AASHTO should clearly designate the
Roadside Design Guide as the definitive
publication for roadside issues.
Task Force Agrees
2. One single definition for the term clear
zone should be adopted
Task Force is preparing a proposal for
the definition
20-7 Project Recommendations
3. 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
20-7 Project Recommendations
4. 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.
20-7 Project Recommendations
4. Need to clarify AASHTO intent on the use of
clear zone dimensions
20-7 Project Recommendations
5. 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.
20-7 Project Recommendations
6. 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.
20-7 Project Recommendations
7. Future editions of the GB and RDG should
contain a single definition for auxiliary lanes.
Task Force agrees
8. 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.
20-7 Project Recommendations
9. AASHTO needs to clarify the relationship
between curbs and clear zone.
Task Force agrees and will propose
changes to the GB and RDG
20-7 Project Recommendations
10. 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.
20-7 Project Recommendations
11. 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.
20-7 Project Recommendations
12. 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.
20-7 Project Recommendations
13. 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
20-7 Project Recommendations
14. 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
20-7 Project Recommendations
15. 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.