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Gradient of Road
Gradient of roads add’s in either assistance or resistance of the vehicle depending upon the type of gradient (down-gradient,up- gradient), hereby either increasing or decreasing SSD.
Kinetic energy is equated to the work done to apply the brakes - Braking distance
Reaction time varies. For young drivers it can be 1-2 sec and older drivers it can be as high as 3-4 seconds.
SSD will be more when you are going downhill (downward slope). Use minus n/100 in formula. For upward slope, use +n/100.
Friction coefficient varies from 0.3-0.4
LAG DISTANCE
The distance traveled by vehicle at uniform design speed during the total reaction time(Tr) is termed as lag distance.
QUESTION- Calculate the lag distance for design speed of 47 km/h for two-way traffic on a single-lane road (assume coefficient of friction as 0.38 and reaction time of driver as 2.5 seconds)
ANSWER-
Concept: Lag distance = 0.278 × V × tR Where, V = Speed in Kmph tR = Reaction time in sec
Calculation: Lag distance = 0.278 × 47 × 2.5 = 32.665
For two way traffic on a single lane lag distance = 2 × 32.665 = 65.33
Reaction distance
The reaction distance is the distance you travel from the point of detecting a hazard until you begin braking or swerving.
The car’s speed (proportional increase):
2 x higher speed = 2 x longer reaction distance.
5 x higher speed = 5 x longer reaction distance.
Your reaction time.
Normally 0.5–2 seconds.
45–54 year-olds have the best reaction time in traffic.
18–24 year-olds and those over 60 have the same reaction time in traffic. Young people have sharper senses but older people have more experience.
Anticipation of hazards.
Preparedness.
The necessity of decision-making (for example, between braking or steering out of the way).
Alcohol, drugs and meditation.
Easy method: Calculate the reaction distance
Formula: Remove the last digit in the speed, multiply by the reaction time and then by 3.
Example of calculation with a speed of 50 km/h and a reaction time of 1 second
50 km/h ⇒ 5
5 * 1 * 3 = 15 meters reaction distance
More precise method: Calculate the reaction distance
Formula: d = (s * r) / 3.6
d = reaction distance in meters (to be calculated).
s = speed in km/h.
r = reaction time in seconds.
3.6 = fixed figure for converting km/h to m/s.
Example of calculation with a speed of 50 km/h and a reaction time of 1 second:
(50 * 1) / 3.6 = 13.9 meters reaction distance
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