4. CHARACTERISTICS OF THE
DRIVER Traffic and transportation engineers are
considering various factors that can affect the
efficiency of transportation. One of these factors is
the driver's characteristics. Varying in their skills
and perceptual abilities where demonstrated by a
wide range of abilities to hear, see, evaluate, and
react to information. Studies have shown that these
abilities may also vary in an individual under
different conditions, such as the influence of
alcohol, fatigue, and the time of day. Therefore, it is
important that criteria used for design purposes be
compatible with the capabilities and limitations of
most drivers on the highway.
5. THE HUMAN RESPONSE
Actions taken by drivers on a road result from
their evaluation of and reaction to information they
obtain from certain stimuli that they see or hear.
However, evaluation and reaction must be carried out
within a very short time, as the information being
received along the highways is continually changing. It
is important that highway and traffic engineers have
some fundamental knowledge of visual perception as
well as of hearing perception.
7. VISUAL ACUITY
Visual acuity is the most common clinical
measurement of how your eyes function. It's
usually one of the first tests taken during a
comprehensive eye exam to determine how
sharp your vision is.
8. Visual acuity test is a critical part of identifying signs of
vision problems.
For example, it can detect refractive errors, more
commonly known as farsightedness and near-
sightedness.
Hyperopia (farsightedness) occurs when you have sharp
far-range vision while your close-range vision is less
clear.
Myopia (near-sightedness) is the opposite, your close-
range vision may be clear, while your far-range vision is
out of focus.
9. Two Types of Visual Acuity
Static Visual Acuity
Dynamic Visual Acuity
10. The driver's ability to identify an object when both
the object and the driver are stationary depends
on his or her static acuity.
Static Visual Acuity
Factors that affect static visual acuity
Background brightness
Contrast
Time
11. Dynamic Visual
Acuity
The driver's ability to clearly detect
relatively moving objects, not necessarily
in his or her direct line of vision, depends
on the driver's dynamic visual acuity.
12. Peripheral Vision
The ability of people to see
objects beyond the cone of
clearest vision. Although
objects can be seen within
this zone, details and color
are not clear.
13. Color Vision
The ability to differentiate one
color from another, but
deficiency in this ability, usually
referred to as color blindness, is
not of great significance in
highway driving because other
ways of recognizing traffic
information devices (e.g., shape)
can compensate for it.
14. Glare Vision and
Recovery
Glare vision
Glare
Recovery
- Glare is light that interferes with your vision,
making it difficult to see or sometimes making
your eyes water.
- is the time required by a person to recover from
the effects of glare after passing the light source.
15. Two types of Glare Vision
Direct Glare
Specular Glare
16. Depth Perception
Affects the ability of a person to
estimate speed and distance. It
is particularly important on two-
lane highways during passing
maneuvers, when head-on
crashes may result from a lack of
proper judgment of speed and
distance.
17. Hearing Perception
The ear receives sound stimuli, which is
important to drivers only when warning
sounds, usually given out by emergency
vehicles, are to be detected. Loss of some
hearing ability is not a serious problem,
since it normally can be corrected by a
hearing aid.
20. 04
The driver sees a
control device, warning
sign, or object on the
road.
The driver identifies the object
or control device and thus
understands the stimulus.
PERCEPTION IDENTIFICATION
21. 04
The driver decides what
action to take in response to
the stimulus; for example, to
step on the brake pedal, to
pass, to swerve, or to
change lanes.
The driver actually
executes the action decided
on during the emotion sub-
process.
EMOTION
REACTION OR
VOLITION
22. Time elapses during each of these
subprocesses. The time that elapses from the
start of perception to the end of reaction is the
total time required for perception, identification,
emotion, and volition, sometimes referred to as
PIEV time or (more commonly) as perception-
reaction time.
23. ⚫ An important factor in the determination of
braking distances, which in turn dictates the
minimum sight distance required on a highway and
the length of the yellow phase at a signalized
intersection.
⚫ Varies among individuals and may, in fact, vary
for the same person as the occasion changes.
⚫These changes in perception-reaction time
depend on how complicated the situation is, the
existing environmental conditions, age, whether the
person is tired or under the influence of drugs
and/or alcohol, and whether the stimulus is
PERCEPTION –
REACTION TIME
24. TRIGGS AND HARRIS
• They noted that the 85th-percentile time to
brake, obtained from several situations,
varied from 1.26 to over 3 seconds.
25. The reaction time selected for design purposes should,
however, be large enough to include reaction times for most
drivers using the highways. Recommendations made by the
American Association of State Highway and Transportation
Officials (AASHTO) stipulate 2.5 seconds for stopping-sight
distances. This encompasses the decision times for about 90
percent of drivers under most highway conditions. Note,
however, that a reaction time of 2.5 second may not be
adequate for unexpected conditions or for some very
complex conditions, such as those at multiphase at-grade
intersections and ramp terminals. For example, when signals
are unexpected, reaction times can increase by 35 percent.
27. As older drivers seem to be depending more on the
automobile for meeting their transportation needs, it
is very important that traffic and highway engineers
consider these diminished characteristics of older
drivers in making decisions on highway design and
operational characteristics that are influenced by
human characteristics.
28. Specific declining abilities of older drivers include reduced visual
acuity, ability to see at night, and flexibility and motion range. This
group also suffers from narrower visual fields, greater sensitivity to
glare, higher reaction times, and reduced muscle strength, which may
result in the older driver having a higher crash risk. For example,
reduction in visual acuity results in older drivers being less capable
to discern letters on road signs, while greater sensitivity to glare
results in older drivers taking a much longer time in recovering from
the disabling effect of glare and may therefore fail to respond to
roadway signs or roadway obstacles, particularly at work zones.
