ITE Journal - March 2020 - 29

Background

Outreach and Survey

With the importance of this topic and the amount of study devoted to
it, a consensus has been difficult to reach over the years on the most
appropriate method of timing the yellow change and red clearance
intervals at traffic signals. ITE published a proposed recommended
practice in 1985 titled Determining Vehicle Change Intervals that was
not ratified by the ITE International Board of Direction to become a
recommended practice.2 Nine years later, ITE published an informational report titled Determining Vehicle Signal Change and Clearance
Intervals.3 In 2001 ITE published another informational report,
A History of the Yellow and All-Red Intervals for Traffic Signals,
summarizing the development of practice up to that year.4
In the interim, changes in technology, automated enforcement, the
availability of new primary data, further research, as well as the public
and professional concern that a defined standard of reference did not
exist with regard to this topic, have led to the initiative to develop this
report. Conversations between ITE leaders and the Federal Highway
Administration identified specific guidance on engineering methods
for traffic signal change and clearance intervals as a gap in engineering
practice in the period. This took place immediately prior the October
2007 release of the request for proposals for the National Cooperative
Highway Research Program (NCHRP) project that would become
NCHRP Report 731: Guidelines for Timing Yellow and All-Red Intervals
at Signalized Intersections.5 However, ITE's development process for
recommended practices follows a different development model than
NCRHP projects, and includes peer review, a public comment period
on the proposed recommended practice, and an appeals process.
ITE began the initial work drafting a recommended practice
with launch of the NCHRP project in 2008. An initial draft of the
report was completed prior to the release of NCHRP 731 in 2012.
Subsequently, the recommend practice was completely revised by
the volunteer technical committee, as well as a round of review panel
comments leading to the release of the proposed recommended
practice in February 2015. The technical committee, with ITE staff
support, worked through addressing the public comments with
detailed responses to each commenter and the review panel completed
another evaluation on the resulting document. As result of this input
and hundreds of individual comments from the technical committee,
review panel, and public across multiple drafts, the recommended
practice was reviewed and responses prepared. In September 2018,
ITE issued a Notice of Intent to Adopt the recommended practice,
which was appealed. The technical committee-again working with
ITE staff-prepared responses to the appeals, the technical committee
made changes where there was agreement, and ITE issued a second
Notice of Intent Adopt, that was also appealed. This led to the
convening of an Appeals Panel on August 28, 2019 and the ensuing
guidance providing direction for concluding the technical revisions to
the final version of Guidelines for Determining Traffic Signal Change
and Clearance Intervals Recommended Practice.

A survey of practice on the subject was coordinated between ITE and
the NCHRP research project team, and ITE staff acted as a liaison
to the research project. The survey sought to identify differences
and similarities in methods and factors used in traffic signal change
interval practices from a cross-section of national and international
agencies. The results of the survey are shared in the state of the practice
section of the recommended practice for each topic related to methods
and values for determining yellow change and red clearance intervals.
During the development period, ITE hosted several roundtable
discussions at its Annual Meetings and technical conferences where
the needs of public agencies were clearly outlined. In addition, a
number of individuals who would eventually become appellants
presented their approaches at the ITE Annual Meetings in
Anaheim, CA, USA and Hollywood, FL, USA.

Purpose and Intended Use
While municipal, county, and state jurisdictions have defined
practices or procedures on the determination of change and
clearance intervals at signalized intersections, historically there
has been a lack of consensus best practices available in the United
States and Canada. The guidelines are based not only upon existing
information found during the initial research, but also on the
collective experience of ITE staff, committee members, peer review
panel, and others who participated in the development process.
ITE's intent for the proposed recommended practice is to
reflect a thoughtful balance between sound engineering theory
and practical application. The recommendations presented in the
report should yield reasonable times for the yellow change and red
clearance intervals for traffic signals. These will allow the profession
to balance those durations while enhancing intersection safety,
maintaining reasonable traffic flow, and providing for movement of
vehicles, bicycles, and pedestrians. The goal of the recommended
practice is to create a consensus methodology for calculating and
evaluating traffic signal change intervals that can be uniformly and
consistently implemented by transportation agencies.
This report should not supersede engineering judgment. It is
anticipated this document will be updated periodically to refine the
procedures based on experiences of agencies using it and studies
performed by the research community. Note that this report is specifically focused on the timing of traffic signal change intervals and does
not discuss or intend to discuss pedestrian signal change intervals.

State of the Practice and Current Research
The report describes the sources of methods and values presented
in the recommended practice to address the goal of the engineering
profession to determine the appropriate duration of yellow change
and red clearance intervals that provide for intersection safety while
retaining a high level of operational efficiency. A broad cross-section of
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ITE Journal - March 2020

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https://www.nxtbook.com/ygsreprints/ITE/ITE_June2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_May2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_April2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_March2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_February2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_January2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_December2019
https://www.nxtbook.com/ygsreprints/ITE/G110939_ITE_November2019
https://www.nxtbook.com/ygsreprints/ITE/G110110_ITE_October2019
https://www.nxtbook.com/ygsreprints/ITE/G110109_ITE_September2019
https://www.nxtbook.com/ygsreprints/ITE/G108559_ITE_August2019
https://www.nxtbook.com/ygsreprints/ITE/G108250_ITE_July2019
https://www.nxtbook.com/ygsreprints/ITE/G107225_ITE_June2019
https://www.nxtbook.com/ygsreprints/ITE/G104039_ITE_May2019
https://www.nxtbook.com/ygsreprints/ITE/G104038_ITE_April2019
https://www.nxtbook.com/ygsreprints/ITE/G104036_ITE_March2019
https://www.nxtbook.com/ygsreprints/ITE/G103582_ITE_February2019
https://www.nxtbook.com/ygsreprints/ITE/G102868_ITE_January2019
https://www.nxtbook.com/ygsreprints/ITE/G100155_ITE_December2018
https://www.nxtbook.com/ygsreprints/ITE/G100154_ITE_November2018
https://www.nxtbook.com/ygsreprints/ITE/G99495_ITE_October2018
https://www.nxtbook.com/ygsreprints/ITE/G98028_ITE_September2018
https://www.nxtbook.com/ygsreprints/ITE/G97366_ITE_August2018
https://www.nxtbook.com/ygsreprints/ITE/G96287_ITE_July2018
https://www.nxtbook.com/ygsreprints/ITE/G94315_ITE_June2018
https://www.nxtbook.com/ygsreprints/ITE/G93877_ITE_May2018
https://www.nxtbook.com/ygsreprints/ITE/G93065_ITE_Apr2018
https://www.nxtbook.com/ygsreprints/ITE/G91484_ITE_Mar2018
https://www.nxtbook.com/ygsreprints/ITE/G89434_ITE_Feb2018
https://www.nxtbook.com/ygsreprints/ITE/G86608_ITE_Jan2018
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