ITE Journal - March 2021 - 31

Colour Blind Awareness

But to a road user with color vision deficiency (typically referred
to as " color-blindness " ), and even more so to those who are fully
colorblind, these colors have little or no meaning.
Grey means stop. Grey means go.
An estimated 4 to 5 percent of the population has some sort of
color vision deficiency. The effects of colorblindness in transportation are not well-documented, and transportation professionals
have generally ignored or misunderstood the issue. What is known
is that colorblindness introduces a disadvantage to some road
users, and the lack of mitigation for this issue makes their travel
experience less efficient and less safe.

Color Vision Basics
The act of sight starts with rods and cones. Two photoreceptors on
the retina take information from the environment, through the
eyes, and to the brain. The rods handle light-related information,
and the cones handle color. The three cones take certain areas of
the spectrum to the brain-red (R), green (G), or blue (B)-like an
old " RGB " computer monitor. The combination of these three cones
creates color vision.
If any of the cones has a problem, the color absorbed by that
cone changes, which affects the RGB combination received by
the brain. Because any one of the cones can have a problem (or be
missing altogether), the type and severity of color vision deficiency
are nuanced. No colorblind person sees the world in exactly the
same way as another, which is one reason addressing this issue is
complicated. 
The most common type of color vision deficiency is Deuteranomaly, a malfunctioning of the green cone. A red cone
malfunction, called Protanomaly, is also possible. Rarely, one of
these cones may be missing altogether; this is called Deutronopia
(green) or Protanopia (red). Rarer still are malfunctioning or
missing blue cones, called Tritanomoly and Tritanopia.
The cone problems that cause colorblindness affect more than a
single color. Any faulty or missing cone (red, green, or blue) impacts
color identification along the entire spectrum. Overall, color
perception tends to be lower, increasing color confusion and the
ability to " call out the color " when seen. This can have significant
effects as travelers navigate the transportation system, as described
below.

Color in the MUTCD
The Manual on Uniform Traffic Control Devices (MUTCD) is the
national standard in the United States that guides the use of traffic
control devices, including signs, pavement marking, and traffic
signals. The MUTCD requires consistent color nationally to provide
uniformity. The manual mentions color more than 300 times,
starting on page 1.

Figure 1. Simulation approximating what some colorblind people see.
" Devices should be designed so that features such as size, shape,
color, composition, lighting or retroreflection, and contrast
are combined to draw attention to the devices; that size, shape,
color, and simplicity of message combine to produce a clear
meaning... " 1
The MUTCD then lays out its official " Color Code " that assigns
proper usage to each color:
The general meaning of the 13 colors shall be as follows:
a.	 Black - regulation
b.	 Blue - road user services guidance, tourist information, and
evacuation route
c.	 Brown - recreational and cultural interest area guidance
d.	 Coral - unassigned
e.	 Fluorescent Pink - incident management
f.	 Fluorescent Yellow-Green - pedestrian warning, bicycle
warning, playground warning, school bus and school
warning
g.	 Green - indicated movements permitted, direction guidance
h.	 Light Blue - unassigned
i.	 Orange - temporary traffic control
j.	 Purple - lanes restricted to use only by vehicles with
registered electronic toll collection (ETC) accounts
k.	 Red - stop or prohibition
l.	 White - regulation
m.	 Yellow - warning
A review of this list reveals several colorblind-related concerns:
ƒ	 Red and green are the most confused colors, yet they are
used for opposite messages: stop and go.
ƒ	 Blue is used for evacuation routes, a true emergency.
Purple-which colorblind people often confuse with blue-is
focused on toll collection, a non-emergency situation.
w w w .i t e.or g

M a rch 2021

31


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ITE Journal - March 2021

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