1) Sight distance refers to the distance a driver can see along the roadway to detect stationary or moving objects. Restrictions to sight distance can occur at horizontal and vertical curves as well as intersections. 2) Stopping sight distance is the minimum sight distance needed for a vehicle traveling at the design speed to stop safely without colliding with an obstruction. It is affected by the vehicle's speed, the driver's total reaction time, road friction, and gradient. 3) The PIVE theory splits a driver's total reaction time into four parts: perception time, intellection time, emotion time, and volition time - the time taken between recognizing an obstacle and applying the brakes. Lag distance

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Prepared by ,
khushboo patel ( B.E civil engg.)
Highway engineering

2. 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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3.  Restrictions to sight distance may be caused as shown in fig.
• Sight distance at horizontal curve
http://www.tpub.com/inteng/11.htm16.gif 3

4. • Sight distance at vertical curve
http://www.msha.gov/training/surfhaul/images/slide6.jpg
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5. • Sight distance at intersection
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/images/3-2.png
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7. 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 7

8. http://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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9. Factors affecting stopping sight distance
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10.  1) speed of vehicle :
https://encrypted/tbn1.gstatic.com/images?q=tbn:ANd9GcTJk56HWGT5GXbpWSsGFElb5384HgIeyKfqcB4cqKwu9xy69dSm
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11.  2) total reaction time of the driver :
http://www.hk/phy.org/contextual/mechanics/kin/eq_motion/6-01.gif
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12.  3) friction resistance between the road & tyres :
https://www.koroad.or.kr/images/en/img_know38.jpg
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13.  4) gradient of road :
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14. http://webarchive.nationalarchives.gov.uk/20061101091400/http://ordnancesurv
ey.co.uk/images/userImages/misc/education/gradient.gif
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15. Analysis of SSD:
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16. Lag distance
 Definition : 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 16

17. What is PIVE Theory ?
 Acc. To PIVE theory the total reaction time of the driver is split
into four parts .
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18. 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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19. http://www.arrivealive.co.za/images/stoppingdistance.jpg
https://m2.behance.net/rendition/pm/703187/disp/859cc9a079eca4b5556af04b
3aa6215c.png
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20. 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.
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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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