Highway engg.
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Transcript of Highway engg.
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Prepared by , khushboo patel ( B.E civil engg.)
Highway engineering
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SIGHT DISTANCE
Definition : The actual distance along the road surface , which a driver
from a specified height above the carriageway has visibility of stationary or moving object is known as sight distance.
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Restrictions to sight distance may be caused as shown in fig.
• Sight distance at horizontal curve
http://www.tpub.com/inteng/11.htm16.gif
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• Sight distance at vertical curve
http://www.msha.gov/training/surfhaul/images/slide6.jpg
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• Sight distance at intersection
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/images/3-2.png
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Types of
sight distanc
e
Stopping sight
distance
Overtaking sight
distance
Site distance at intersectio
n
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Stopping sight distance (SSD)Definition : The minimum sight distance available on a
highway to stop a vehicle travelling at design speed , safely without collision with any other obstruction is xalled stopping distance.
https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcQFKpIxAAAbJH3n64ECpY2EHIf-mjYUXedmQ0WUPheL5hqfngHS
8http://www.ite.org/css/online/img/Figure10-5.jpg
• For the purpose of measuring stopping sight distance , IRC has suggest clear sight triangle as shown in fig. ,
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Factors affecting stopping sight distance
Speed of
vehicle
Efficiency of brakes
Total reaction time of driver
Friction resistance
between road & tyres
Gradient of the road
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1) speed of vehicle :
https://encrypted/tbn1.gstatic.com/images?q=tbn:ANd9GcTJk56HWGT5GXbpWSsGFElb5384HgIeyKfqcB4cqKwu9xy69dSm
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2) total reaction time of the driver :
http://www.hk/phy.org/contextual/mechanics/kin/eq_motion/6-01.gif
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3) friction resistance between the road & tyres :
https://www.koroad.or.kr/images/en/img_know38.jpg
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4) gradient of road :
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http://webarchive.nationalarchives.gov.uk/20061101091400/http://ordnancesurvey.co.uk/images/userImages/misc/education/gradient.gif
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Analysis of SSD:
Lag distanc
e
Breakin
g distance
Stopping sight distance
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Lag distanceDefinition : The distance travelled by the vehicle during
the total reaction time is known as lag distance .
Reaction time of the driver is the time taken from the instant the object is visible to the driver to the instant the brakes are effectively applied.
http://www.hk/phy.org/contextual/mechanics/kin/eq_motion/6-01.gif
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What is PIVE Theory ?Acc. To PIVE theory the total reaction time of the driver is
split into four parts .
Perception time
Intellection time
Emotion time
Volition time
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1) Perception time : It is the time required for the sensations received by the eyes
or ears to be transmitted to the brain through the nervous system .
2) Intellection time : It is the time required for understanding the situation.
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http://www.arrivealive.co.za/images/stoppingdistance.jpghttps://m2.behance.net/rendition/pm/703187/disp/859cc9a079eca4b5556af04b3aa6215c.png
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3) Emotion time : it is time elapsed during emotional sensations & Disturbance
such as fear , anger ,etc. with reference to the situation . 4) Volition time : volition time is the time taken for the final action.
Lag distance = v * t
Where, v = speed of vehicle in m/s t = total reaction time (s) [ as per IRC t = 2.5 s ]
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Have a nice day.