ITE Journal - March 2021 - 34

Two Colors. Same Signal Head. 
4D.06.06 Each arrow signal indication shall emit a single color:
red, yellow, or green except that the alternate display (dual-arrow
signal section) of a GREEN ARROW and a YELLOW ARROW
signal indication, both pointing in the same direction, shall be
permitted, provided that they are not displayed simultaneously.1

Addressing the needs of colorblind travelers starts with basic
accessibility principles, and continues with specific examples to
improve safety and efficiency for colorblind travelers, and in turn,
for everyone.

Accessibility Principles
Ian Hamilton, an accessibility specialist in Bristol, England,
identifies three key principles related to colorblindness that I've
adapted to transportation planning, design, and operations.
1.	 Don't use color difference alone to communicate or differential
information.
2.	 Check with a simulator to pick up on contrast issues.
3.	 Run by colorblind folk, but use that as a way to pick up on
issues you've missed, not was a way to verify accessibility.3
Don't Use Color Difference Alone to Communicate or Differentiate Information. As shown below, the London Underground
subway map color lines can be problematic for colorblind travelers.

Brian Chandler

Transport for London, 2020

The MUTCD allows the green arrow and yellow arrow to be
used in the same head location with the only difference being
the color. Note that in this case the figures are not showing the
difference between regular color vision and color deficiency. These
are both normal-color-vision photos of the same signal head, taken
a few seconds after the other.
Of every 20 drivers making this left turn, one is colorblind, and
he or she will struggle to identify that arrow as yellow or green. Those
who are colorblind will make their best guess, and then hope-for
their own safety and that of others-that they guessed correctly.

Solutions

Figure 8. Excerpt of London Underground Map.

Brian Chandler

Figure 6. Four-section signal head with green indication.

Figure 7. Four-section signal head with yellow indication.
34

Ma rch 2021

ite j o u rn al

To help colorblind users, several smartphone apps and websites
provide colorblind-friendly versions of the map. As seen below, this
image displays a normal map view on the left, what some colorblind
viewers see in the middle, and then a double-coded map on the
right that includes a mix of colors and patterns for an aesthetically
pleasing, colorblind-friendly map.
Check with a Simulator to Pick up on Issues. For any situation
where a colorblind perspective is needed, software tools can give
anyone a starting point to approximate what some colorblind users
may see. COBLIS is a browser-based simulator that allows users
to upload an image from their computer and simulate a variety
of color vision deficiencies. At DKS Associates, a consulting firm
focused on transportation solutions, the creative services team
uses Color Oracle, a free plug-in for Mac and Windows that
simulates color vision deficiency. DKS created a color palette for
transportation-related mapping projects that is optimized for
colorblind viewers.


https://www.color-blindness.com/coblis-color-blindness-simulator/ https://www.linkedin.com/company/dks-associates/ https://www.colororacle.org/

ITE Journal - March 2021

Table of Contents for the Digital Edition of ITE Journal - March 2021

ITE Journal - March 2021 - 1
ITE Journal - March 2021 - 2
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