ITE Journal - March 2020 - 30

topics affecting the timing of yellow change and red clearance intervals
are addressed through discussion of the relevant literature, including
the foundational work of DeGazis, Herman, and Maradudin, as well as
research identified in the literature review, the current state of practice,
comments received throughout during the drafting process, and the
recommendations applied in the guidance.6 Those topics include:
ƒƒ Calculation method
ƒƒ Variance in vehicle codes
ƒƒ Perception-reaction time
ƒƒ Speed
ƒƒ Deceleration
ƒƒ Intersection width
ƒƒ Vehicle length
ƒƒ Grade
ƒƒ Minimum and maximum intervals
ƒƒ Rounding calculated intervals
ƒƒ Use and calculation of red clearance interval
ƒƒ Turning movements
ƒƒ Other road users
ƒƒ Special road conditions
ƒƒ Implementation
ƒƒ Safety
ƒƒ Driver behavior
In addition, the report identifies topics recommended by ITE for
additional study or new research that would be helpful to expand
the body of knowledge on this topic (discussed in more detail in Jeff
Lindley's article on page 32).

Recommended Methods of Determining Yellow Change
and Red Clearance Intervals
Summary
The report provides a description of the recommended methods
to calculate traffic signal change and clearance intervals. The
calculation methodology in the report is based on the extended
kinematic equation and is shown in both U.S. and metric units. The
report provides guidance for applying the methodology and for
selecting input values for both through and turning movements at
signalized intersections. Input values include perception-reaction
time, approach speed, deceleration rate, approach grade, intersection width, vehicle length, and conflicting movement start-up delay.
The report notes application techniques for wide intersections and
bicycle traffic. The application of measures of effectiveness and
recommendations for monitoring and evaluation close the report.

What's New
The final recommended practice was updated in response to
comments received on the proposed version of the document and
30

Ma rch 2020

ite j o u rn al

the guidance provided by the panel convened to adjudicate appeals
on the report. As a result there a number of new or revised elements
in comparison to previous practice documents and previous
versions of the proposed recommended practice as follows.
ƒƒ The recommended calculation method uses an extended
kinematic equation formula as the basis for calculation of
change intervals, which is documented in the literature review
(Jay Beeber (M) provides an explanation of Mats Järlström's
derivation of the extended kinematic equation on page 34).
Text and formula references in the guidance emphasize that the
calculation of the yellow interval is the minimum value.
ƒƒ With the use of the extended kinematic equation, the discussion
of application to left turning movements has been expanded
to include intersection entry velocity and an allowance for
the use of longer change intervals for these movements of up
to maximum value of seven seconds. In addition, guidance is
provided for several typical signal phasing methods.
ƒƒ Since there is limited research on the complex nature of
driver behavior, interactions, and theoretical formulation for
right-turn maneuvers, some elements of these factors are not
fully understood. Therefore, more information is necessary
before making a definitive, separate recommendation for change
and clearance intervals for right-turning vehicles.
ƒƒ Inclusion of a simple grade factor in the extended kinematic
equation formulation for non-zero grades.
ƒƒ Supplemental discussion and guidance related to determining
intersection width.
ƒƒ Modification of the discussion on the use of conflicting
movement start-up delay and removing the requirement for the
use of non-zero value.
ƒƒ Use of measured primary data is preferred wherever possible.
ƒƒ An approach for estimating values of approach speeds is offered
for when the primary 85th percentile speed data is unavailable.

Additional Information and
How to Purchase a Copy
Additional information on the recommended
practice, how to purchase, and other
supporting material is available at: https://
www.ite.org/technical-resources/topics/
traffic-engineering/traffic-signal-changeand-clearance-intervals/. The publication
may be purchased through the ITE
Bookstore.
Members: $75.00 (electronic or print format)
Non-members: $150.00 (either format)
MARCH 2020

Guidelines for
Determining
Traffic Signal Change
and Clearance Intervals
A Recommended Practice
of the Institute of
Transportation Engineers


https://www.ite.org/technical-resources/topics/traffic-engineering/traffic-signal-change-and-clearance-intervals/ https://www.ite.org/technical-resources/topics/traffic-engineering/traffic-signal-change-and-clearance-intervals/ https://www.ite.org/technical-resources/topics/traffic-engineering/traffic-signal-change-and-clearance-intervals/ https://www.ite.org/technical-resources/topics/traffic-engineering/traffic-signal-change-and-clearance-intervals/

ITE Journal - March 2020

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