1. 1 shows that studies that have been done



AASHTO Green Book defined braking
reaction time as the interval from the instant that the driver recognizes the
existence of an obstacle on the roadway ahead that necessitates braking until
the instant that the driver actually applies the brakes (AASHTO, 2011).An indicator of the driver
speed to implement a task following a mental processing is brake reaction time.
“It includes the following components the visual perception time, mental
processing time, leg movement time and the device response time”. Many factors
affect brake reaction time like age, gender, mental fatigue, alcohol intake,
sleep deprivation, etc. “It is also affected by the features of the distracting
stimuli, like the size of the object, color of the object, amount of
illumination in the background etc.” ( Ashok, et al., 2016).

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Table 1 shows that studies that
have been done obtained different results of brake reaction time values. The
studies used different criteria for finding the value of brake reaction time;
for example, in 1936, Green Shield used laboratory automobile as the study
criteria, while Sivak et al. (1981) used response to brake light as the study
criteria (McGee, et al.). 


Table 1: Summary of
studies on brake-reaction time (McGee, et al.)


Aim of the Study


The aim of this paper is to study
all of the factors that affect the driver brake reaction time and mention some
studies that have been done as literature reviews.

Brake Reaction Time for Sight Distances


The driver characteristic
perception-reaction time is considered an important factor in a variety of
highway design and operations standards. One of the driver characteristics is sight
distance, which is the length of roadway that a driver can see ahead at any
particular time. There are three types of sight distances: stopping sight
distance (SSD), passing sight distance (PSD), and decision sight distance (DSD)
(AASHTO, 2011).

SSD is the sum of two distances
(AASHTO Green Book, 2011):

1)       The distance traversed by the
vehicle from the instant the driver sights an object necessitating a stop to
the instant the brakes are applied, and 

2)       The distance needed to stop the
vehicle from the instant brake application begins. These are referred to as brake
reaction distance and braking distance, respectively.



design speed, km/hr

Perception – reaction time, sec (AASHTO recommends 2.5 sec. as t)               

rate, m/s2

: Grade, m/m

PSD is the minimum sight distance
required on a two-lane two way highway that will permit a driver to (AASHTO
Green Book, 2011):

Complete a passing maneuver without colliding
with an oncoming vehicle.

Complete a passing maneuver without cutting
off the passed vehicle.

Passing sight Distance Formula:

1 shows the typical diagram of PSD maneuver that includes three distances as

PSD = d1 + d2 +

Figure 1: Typical diagram
of PSD (Bindra)

As shown in the figure, the PSD
can be obtained by adding the three distances that are calculated from some
other parameters as defined in the following:  

d1 = Distance travelled by the
vehicle P from its position P1 during the time in which vehicle P decides
whether or not, he should take over the slow moving vehicle S.

d2 = Distance travelled by the
vehicle at P1 to its position at P2.

d3 = Distance travelled by vehicle
R from position R1 to R2.

V = Design speed of the road in kph.

m = Difference in speed of fast and slow
moving vehicles

a =Rate of acceleration in m/sec2 of
vehicle P.

t = Time required to complete the actual
overtaking maneuver

s = Headway i.e. speed of the vehicles just
before and just after the overtaking operation.






The rate of acceleration (a) is
based on the speed of the vehicles as shown in Table 2 below

Table 2: Acceleration rate
for design speed (Bindra)

Speed  (km/hr)

Acceleration rate (km/hr. sec)
















speed of overtaken vehicle or slow moving vehicles (V-m) is considered as
uniform all long.

= 0.56 (V-m)

d2  = 2s + 0.28 (V-m)*T

depends on the speed of overtaking vehicle; therefore d2 can be
calculated as:

= b + 2*s

= 0.28*(V-m)*T +


a is in m/s2


= 0.28*(V-m)*T +



b =



s =
0.20*(V-m) + 6.0

T =

a is in kph /sec                       


T =


= 2s + 0.28* Vb*T

= 0.28*V*T


When the road is unidirectional and there is no interferences
of the opposite traffic, then d3 becomes zero, and

= d1+ d2

The passing sight distance for two-directional road is as

= d1+ d2 + d3

=0.56*(V-m) + 2*0.2*(V-m) +6.0 + 0.28*(V-m)*T + 0.28*V*T



Assumptions of PSD


1.      The passing or opposing vehicles
travel at the same speed that represents the design speed of the road.

2.      The speed of the vehicle being
passed (impeder) does not vary during the passing maneuver and it is less than
that of the passing vehicle by 19.2 km/h.

3.      The passing vehicle is capable of
accelerating to the passing speed (19.2 km/h higher than that of the vehicle
being passed) within a distance of about 40 percent of the distance covered
during the passing maneuver.

4.      The lengths of the vehicle being
passed and that of the passing vehicle are that for the passenger car design vehicle
(i.e., 5.7 m).

5.      The perception-reaction time of
the driver of the passing vehicle is 1.0 sec for aborting the pass.

6.      The same acceleration rate of 3.41
m/s² used for developing stopping sight distances is used for
aborting a passing maneuver.

7.      Time headway of 1 sec exists
between the passing and impeder vehicles at the end of an aborted or completed

8.      At the point where the passing
vehicle returns to its normal lane, the time headway between the passing and
impeder vehicles is 1 sec.

Despite the formulas for finding
passing sight distance as mentioned before, AASHTO Green book, 2011 showed the
passing sight distances for different design speeds as shown in Table 3. The
passing sights distance values are based on the researches that have been verified
with field observation of passing maneuvers (AASHTO Green Book, 2011).

Table 3: Passing sight
distance for design of two-lane highways (AASHTO, 2011)


DSD is the distance needed for a
driver to detect an unexpected or otherwise difficult-to-
perceive information source or
condition in a roadway environment that may be visually cluttered,
recognize the condition or its
potential threat, select an appropriate speed and path, and initiate and complete
complex maneuvers (AASHTO, 2011).

Because decision sight distance
offers drivers additional margin for error and affords them sufficient length
to maneuver their vehicles at the same or reduced speed, rather than to just stop,
its values are substantially greater than stopping sight distance (AASHTO, 2011).

The decision sight distances,
which are shown in Table 4, may be used to:

1)      Provide values for sight distances
that may be appropriate at critical locations, and

2)      Serve as criteria in evaluating
the suitability of the available sight distances at these locations.



Table 4: Decision sight
distance (AASHTO, 2011)




: design speed, km/hr

: Perception – reaction time, sec                 

Deceleration rate, m/s2

: Grade, m/m

As indicated in the three sight
distances mentioned before, the perception-reaction time for each type of the
sight distances are different; they can be summarized in Table 5.




5:  Brake perception reaction time for the three
types of sight distances (AASHTO, 2011)

Type of Sight Distance

Brake Reaction Time Value, sec








Avoidance maneuver A: Stop on rural road


Avoidance maneuver B: Stop on urban road

10.2 -11.2

Avoidance maneuver C: Speed /path/direction change on
rural road

12.1 -12.9

Avoidance maneuver D: Speed /path/direction change on
suburban road

14.0 -14.5

Avoidance maneuver E: Speed /path/direction change on
urban road


Effect of Brake Reaction Time on Safety


Driver reaction time is one of the
most important measurement components in crash avoidance research (
Sena, et al., 2016). When road accidents are being
reconstructed the accident reconstruction experts are almost without exception
confronted with the determination of driver’s reaction time. Regarding traffic
safety, the driver’s reaction time is the time which runs from the moment of
driver’s perception of danger to the moment of driver’s reaction to the
circumstances either by steering or braking (T.
Magister, 2006). Increases in reaction time can
lead to safety risks on the road. In situations such as the braking response,
the reaction time of the driver is not simply only one step process, but rather
a sequence of complex reactions (
Anderson, et al., 2012).

Literature Review


This literature covers several
studies about the factors that affect brake reaction time such as gender, age,
mental fatigue, alcohol intake, sleep deprivation, and so on.



 Effects of Gender on
Brake Reaction Time


In 2016, J. Ashok, V. Suganthi,
and I. Vijayalakshmi conducted a study to assess the effect of gender on brake
reaction time. The study was done in and around the Veerapandi village in Salem
district, Tamilnadu. They selected 35 male and 25 female drivers whose ages
were between 25 and 35 years and they had been in good health. The study was
done by using a stationary car that was connected to a computer. They used SPSS
statistical software for data analyses. They used a change in the color of
light as the stimulus that presented for the braking response. They obtained
that the males responded faster for the visual stimuli than for auditory
stimuli. Males responded quicker to unexpected stimuli in the experimental
condition than females. As a conclusion, they obtained that brake reaction
times for males are shorter than that for females as shown in Table 6.

Table 6: Mean ± SD of
Brake Reaction Time in male and female drivers ( Ashok, et al., 2016)

As shown in the table, the mean
value of braking reaction time for the females was 0.863, which was greater
than braking reaction time for males, which was 0.640 seconds. They showed than
there is a significant difference between them because the p-value was 0.0007,
which was much lesser than 0.05.


Effect of Age on Brake
Reaction Time


In 2012, Brown conducted a master
study entitled “A Comparison of Drivers’ Braking Responses across Ages”. The
study had two independent variables: age, and test type (complex driving
simulator, simple floor model tester, or simple driving simulator test). It
included two dependent variables: time as measured by seconds and force as
measured by pounds. They concluded that Older drivers’ complex braking reaction
times had greater variability and increased time from their simple reaction
times than did those of the younger participants as shown in Table 7.

Table 7: Brake Reaction
Time (Danielle, 2012)


 Effect of Mental
Fatigue on Brake Reaction Time


Driving fatigue is a common
phenomenon during driving, and is a hot research topic in the field. Fatigue has a remarkable impact on a driver’s
perceptions, attention, decision-making and judgement. The control ability of a
vehicle is directly determined by a driver’s reaction ability during driving
performance ( Guo, et al., 2016).

      Guo et al. conducted a research about
relationship between reaction ability and mental state for online assessment of
driving fatigue. The relationship between driving fatigue, physiological
signals and driver’s reaction time was analyzed. Twenty subjects were tested during
driving. All the subjects who held a driving license were screened for
eligibility. Twelve males (60%) and eight females (40%) were voluntarily
recruited for this research from the general public. Their ages ranged from 24
to 51, and their driving experience ranged from three years to 25 years. It was
ensured that the subjects had sufficient sleep, with no alcohol or coffee for
24 hours prior to participation in the experiments. In the experiment a
simulator, a biopac system, a reaction time test system and a computer was
used. Grey correlation analysis was used to select the input variable of the
classification model. A support vector machine was used
to divide the mental state into three levels.

The three levels (self-assessment
method) were proposed based on Stanford Sleepiness scale in order to allow the
driver to also perform a self-assessment quickly and intimately. Level 1
represented the drivers in a state of vigilance. Level 2 represented the drivers
with slight mental fatigue. Level 3 represented the drivers with serious mental
fatigue. The detailed scale statements of the levels is shown in Table 8 below


Table 8: Self-assessment
scale ( Guo, et al., 2016)


The study also regarded age and
gender of drivers for different mental levels. As shown in Figure 2, Level 1
had lower reaction time as indicated by the black data line; Level 3 (red data
line) had the greatest reaction time, while the reaction time in Level 2 (blue
data line) was in between them.


Figure 2: The relationship between
reaction time, age, gender and mental fatigue levels

( Guo, et al., 2016)


On the other hand, the study obtained
different results of braking time for different mentality fatigue regarding
gender of drivers as shown in Table 9.

Table 9: The average
reaction time of different mental level ( Guo, et al., 2016)

As indicated in the table, it is
clear that Level 3 had the largest average reaction time, while Level 1 had the
lowest average reaction time, which indicates that the reaction time becomes
longer as mental fatigue accumulates.
The study concluded that females
had a longer reaction time than males when driving fatigue accumulated. The
stamina of females was poorer than males, which indicates that females may get
fatigued faster than males. Moreover, there was a difference between males and
females for the same mental level. The reaction time of females had been found
to be longer than males for each mental level. The higher the mental level, the
bigger the gap between males and females.

They also considered the age of
drivers as is another significant factor that can influence the reaction time.
The results of the average reaction time of different age groups are shown in
Table 10.

Table 10: The average
reaction time of different age groups ( Guo, et al., 2016)

The age of drivers were divided
into two groups: age 20–30 years, and over 30 years. This type of driver may
have a long reaction time.

As a result of the study, they
concluded that females have a faster decrease in reaction ability than males when
driving fatigue accumulates. Elderly drivers had longer reaction times than the
young drivers.

Talusan, et al.,
(2014) investigated the difference in
brake reaction times of night float and post-call physicians in training. In
this study conversion of a night float schedule for overnight coverage was
assessed. Participants were trainees in their first to fourth years of training
at Yale- New Haven Hospital. Only physicians in training who had driven a car
in previous six months were allowed to be participants. Exclusion criteria were
included not driving cars regularly or injuries to the lower extremities
(sprain, fracture, other lower extremity pain). Participants were in internal
medicine and orthopaedic surgery filled out a survey that involved the Epworth
Sleepiness Scale (a subjective measure of a participant’s sleepiness), their
age, year in residency, and specialty. Between 7 am and 9 am the participants
were again approached for post-shift survey and reaction time testing. Driving simulator
was used to record brake reaction time. Several groups of interest were
established as variables: all interns, all residents, orthopedic interns and
residents, internal medicine interns and residents, night float shift
participant and those on traditional 28-hour call shifts. As a statistical
criterion, a paired sample t-test was used to compare the reaction times.
Wilcoxon signed rank test was conducted to compare results from the Epworth
Sleepiness Scale for each group. It was found that there is an overall increase
in reaction times for post-call trainees compared to pre-call trainees.

They obtained that after a
traditional 28-hour call shift, trainees had significantly worse brake reaction
times than they did prior to their shift, whereas trainees
on night float rotations had non-significant increases in brake reaction times
post-shift. Both groups had higher post-shift scores on the Epworth Sleepiness
Scale, which suggests that participants in each group were sleepier post-shift,
despite the fact that the night float group had no significant difference in
brake reaction times.


of Alcohol Intake on Brake Reaction Time


            Christoforou in 2013 studied
the influence of alcohol on reaction times for young impaired drivers. The
behavior of young driver under the influence of alcohol was explored by using
driving simulator experiment. Forty nine participants were subjected to a
common pre-defined dose of alcohol consumption and the subjects underwent five
different stages in the experiment. The study was conducted by using breath
test for knowing the level of drinking alcohol from drivers.  The results of the breath of all independent
variables considered along the experiment with summary statistics were
summarized in Table 11.

Table 11: Explanatory
variables in reaction time analysis ( Christoforou, et al., 2013)

According to the table, different
reaction times were obtained for different drinking levels from drivers. For
example, the reaction time was 1.2 seconds for BrAC1/3; while, the reaction
time was 0.3 second for BrAC-1. These different obtained values of the reaction
times were based on time after alcohol ingestion from the drivers.

the analytic technique of the study, multiple linear regressions were used to
model the relationship between a continuous dependent variable and several
regressors. Several parameters relating to the drivers characteristics were
modeled, and named as model 1 type and model 2 types as shown in Tables 12 and







Table 12: Model estimation
results for model type 1 ( Talusan, et al., 2014)

Table 13: Model estimation
results for model type 2 ( Talusan, et al., 2014)



The results of this study shows that the braking reaction
time depends on several factors such as gender, age, mental fatigue, alcohol
intake by drivers, etc. Despite the factors that affect the braking reaction
time, the braking reaction time is different based on the type of vehicle
maneuvers or sight distances such as SSD, DSD, and PSD. However the braking
reaction time is based on several factors as mentioned before, AASHTO recommend
2.5 seconds for design of geometric elements based on SSD, 1 second for PSD,
and greater different values for DSD.


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