ITE Journal - March 2021 - 32

United States, as the forests change colors to an array of green,
red, yellow, and orange-the same color as many highway signs.
The problem is exacerbated when the signs fade over time, making
them blend in even more with their surroundings. The image below
simulates what someone with Deutronopia (green-blind) color
vision deficiency may see.

Signing
Traffic engineers use signs to share information with road users,
and color is one of the primary aspects of the sign denoting
its type. For example, all red or partially-red signs are called
" regulatory " signs, warning signs are yellow, work zone signs
are orange, and other colors are used for other types of signs as
described above.

Figure 3. Left: Stop sign with background vegetation. Right: That same
image as seen by some colorblind road users.

Speed Limits, Speed Advisories, and Color
One example of sign color confusion is the way traffic engineers
post speeds. There are three different types of speed-related signs
on the roadway:

Modified from MUTCD

Regarding roadway striping, the MUTCD requires that " Markings
shall be yellow, white, red, blue, or purple " and details the purpose
of each color:1
ƒ	 White: Separation of traffic in the same direction,
right-hand edge of road.
ƒ	 Yellow: Separation of traffic in opposite directions, left-hand
edge of divided highways, one-way streets, and some ramps.
ƒ	 Red: Truck escape ramps, lanes that should not be entered
in the direction from which the markings are visible.
ƒ	 Blue: Supplement white markings for disabled
parking spaces.
ƒ	 Purple: Supplement other markings in toll plaza areas;
designate areas restricted to vehicles with electronic toll
plaza accounts.
ƒ	 Black: Contrast marking, only used in combination with
other colors.
Using color alone to differentiate regulations can be
problematic for colorblind road users. For instance, colorblind
drivers could misidentify yellow skip lines on their left
as white skip lines, assuming the lane to their left is in the same
direction they themselves are traveling. This momentary mistake
can happen quickly and subconsciously, and the result could be a
head-on collision.

For colorblind road users, it is common for signs (especially green,
red, yellow, and orange) to visually blend in with the environment.
This is of particular concern in the autumn in many parts of the
32

Ma rch 2021

ite j o u rn al

State of Michigan

Blending in with the Environment

Figure 4. Left: Two-way, two-direction roadway with a yellow skip
marking. Right: a multi-freeway with white skip lane marking.

Flickr Commons/haljackey

Pavement Marking

Figure 2. Variety of posted speeds.
ƒ	 Regulatory Speed Limit - These signs provide a speed limit
that, if exceeded, could result in a driver receiving a citation.
ƒ	 Advisory Speed Limit - These signs are typically added at the
bottom of a warning sign, have a yellow background, and
are only a suggestion. Exceeding an advisory speed is not
breaking the law.
ƒ	 Work Zone Speed Limits and Advisory Speeds - In some
cases, a work zone will have a regulatory work zone speed
limit. But a work zone may also have an advisory speed
plaque under work zone warning signs (orange background)
to denote a recommended speed.
Colorblind drivers may not be able to easily tell whether the
speed sign is regulatory or advisory, putting them at a disadvantage
since they cannot easily use color as a distinguisher.

Image from The Bluffton Sun; simulation via Colbindor

ƒ	 Light blue and coral are currently unassigned, but if either is
introduced it is likely to cause confusion.
ƒ	 Fluorescent pink signs, used to warn road users of incidents,
test poorly for colorblind people, looking more like faded
red, yellow, or grey.



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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