Download 20-7HFG -CMFReview - American Association of State Highway

NCHRP 20-7
Proposed Research Needs Statement
Submitted by:
Highway Safety Performance Committee – ANB 25; Dr. John Milton
Human Factors Road Design Guides Subcommittee – AND 10(2); Dr. Samuel C. Tignor
Date: July 30, 2014
Title: “Assessment of Varied Interpretations Between HFG Guidelines and CMF”
Background/Needs Statement:
Today there are two new tools available for planning and designing roads and assessing their
safety. They are the “Highway Safety Manual” (HSM) and the “Human Factors Guideline for
Road Systems” (HFG). The HSM is for estimating the safety of roadway infrastructure. The
HFG is to facilitate safe operational decisions by providing the best factual information and
insight on road users’ needs. Together these two documents enable highway planners, designers
and traffic engineers to incorporate features to promote the highest level of safety for new or
upgraded roadways. Both documents were conceived by TRB standing committees, developed
with NCHRP support and are now available to highway planners, designers, and traffic
engineers.
Crash modification factors (CMF) are an essential component of using the HSM for estimating
road safety. They are used as part of the HSM computational process. The FHWA Clearinghouse
for CMF has compiled hundreds of CMF for numerous safety treatments and countermeasures.
The CMF have been assigned star ratings (in a scale of 1-5) to aid users by rating the
methodology used to develop the CMF. This assists users in deciding adequacy of a CMF by for
given project applications. In short, they are used to compare various treatments and for helping
in the selection of treatments that are best for the given projects. The star ratings are assigned
based on the review of research reports and the confidence in the results of the study producing
the CMF. Guidelines contained within the HFG are developed based on the soundness of human
factors research undertaken on specific safety treatments. Each guideline within the HFG is
accompanied by a scale rating, (based in linear steps from “primarily expert judgment” to
“primarily empirical data”) showing the soundness of the guideline based on the review of many
research reports that address how successfully road users can use the treatment. If insufficient
definitive human factor research is available, no guideline is developed or based on that
individual topic. The HFG guidelines are accompanied by a short review of the research so the
user will have a better understanding of the how the treatment performs and is accepted by the
road user. Taken together both the HFG and HSM crash modification factors, collectively, have
given the designer, planner, and traffic engineer better information on the performance and user
acceptance of given treatments than their safety tool boxes have done previously.
While differences can sometimes occur when comparing given treatment CMF and HFG
guidelines, it is not a case that either is wrong. It can occur based on when the research for the
CMF and the HFG guidelines were actually developed and made available. If the time the
respective research was done were years apart, the soundness of the research in the experimental
plans, whether the traffic and geometric conditions of the CMF and HFG guidelines were
comparable, whether statistical tests were appropriate for the data, and other factors can
individually or collective have a big impact on the Star rating and whether a HFG guideline was
written are considerations that may explain these differences.
The goal of this exploratory research is to determine (1) if safety treatments that differ between
what is available in the CMF clearinghouse and the HFG guidelines should be a concern to the
designer, planner, or traffic engineer, and (2) how difficult what the issues will be in assessing
the two documents for these kinds of conditions. What is sought are recommendations on how
these two situations can be best addressed across the entire set of CMF and all of the multiple
HFG guidelines.
It should be noted item 1 also includes the situation where, for specific safety treatments, there is
no Star rating provided but a HFG guideline is provided, or vice versa.
Research Objective:
The objectives are: (1) to review and screen the basis of the CMF and HFG guidelines to
determine if there is a suitable and practical way in which different or missing CMF or HFG
guidelines can be identified for safety treatments, and, (2) to make recommendations on how and
what the HFG and HSM documents should tell designers, planners and traffic engineers to do in
such situations. While the number of these differences between the two approaches may be
relatively small, users seek guidance on how to resolve them in selecting project safety
improvements/treatments.
Work Tasks:
The following tasks of this exploratory research is to help (1) understand the potential scope of
the problem that may arise in selecting appropriate CMF and HFG guidelines when
recommendation differences are detected between the two methods, and (2) provide guidance to
designers, planners, and traffic engineers in resolving the differences. It should be noted the HFG
guidance is specifically associated with road-user perception and understanding of infrastructure
design and operations experienced and the HSM is a quantified safety estimate.
1. Review the procedures used in establishing (1) CMF for the HSM models and (2) how
guidelines are selected for inclusion in the HFG.
2. Review the comparability of CMF Star ratings and the research reliability scale used in
the HFG.
3. Identify candidate procedures to use when given safety treatment CMF values and HFG
recommendations differ sufficiently to place the selection and use of the treatment in
question. This includes the case when either of the two approaches do not address given
safety treatments.
4. Given the large number of CMF and HFG guidelines that have been developed, identify
candidate screening procedures that could be used to identify conflicting safety results.
5. Recommend how frequently CMF values and HFG guidelines for the identical treatments
should be reviewed.
6. In cases for given safety treatments when there is a difference in whether there is a CMF
provided in the Clearinghouse as compared to a suggested HFG guideline, recommend
how designers, planners and traffic engineers might proceed in developing project safety
recommendations.
Urgency:
The HFG and HSM are both gaining recognition and acceptance as essential highway safety
tools. About 27 percent of highway fatalities are associated with road and user interaction
problems. The problems may be design oversights, inadequate time for proper user decision
making, or other similar situations. The HSM and HFG were developed to help road designers,
planners and traffic engineers make design and operational decisions that are compatible with
road users’ needs and capabilities. This exploratory effort will identify potential approaches in
how CMF and HFG guideline differences could be resolved. Both of these documents are being
increasingly used daily by highway safety analysts and their continued use is highly desirable.
Funding Requested and Time Required:
It is estimated that this research will take 18-months to complete and will require no more than
$50,000.
Contact Person:
Dr. John Milton, PE
Director, Enterprise Risk Management
Washington State Department of Transportation
310 Maple Park Avenue SE
Lacey, WA 98503-1147
P.O. Box 47418
Olympia, WA 98504-7418
Phone: 360-704-6363; 360-791-9242
Fax: 360-704-6367
[email protected]
Developers of Research Problem Statement:
Dr. John Milton, PE
Director, Enterprise Risk and Safety Management
Washington State Department of Transportation
310 Maple Park Avenue SE
Lacey, WA 98503-1147
P.O. Box 47418
Olympia, WA 98504-7418
Phone: 360-704-6363; 360-791-9242
Fax: 360-704-6367
[email protected]
Dr. Samuel C. Tignor, PE, ASCE Fellow, ITE Member, and retired FHWA R & D
Chair of TRB Human Factors Road Design Guides Subcommittee, AND10(2)
1706 Fairview Avenue, McLean, VA 22101
703-356-1037
[email protected]
Thomas Hicks, PE
Director of Business Development
Century Engineering, Inc.
10710 Gilroy Road
Hunt Valley, MD 21031
443-589-2400x1323
[email protected]