Clear Zone Conflicts in AASHTO Publications

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 lt400) 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 (lt400 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.
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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.