The document discusses the essential requirement for overtaking sight distance (OSD) for vehicles, outlining the factors affecting it and analyzing the components of OSD on a two-way road. It emphasizes the importance of providing adequate overtaking zones at frequent intervals where there is potential for overtaking, and details the necessary calculations for determining OSD, including driver reaction time and spacing between vehicles. Additionally, it mentions the concept of intermediate sight distance (ISD) when OSD cannot be accommodated.

1. OVERTAKING SIGHT
DISTANCE
PRESENTED BY
AGLAIA

2. OVERTAKING REQUIRMENT
 All vehicles dont travel at design speed 
 Need to overtake slow moving traffic by fast moving vehicles
 Adequate sight distance for overtaking should be provided along the
alignment
 The minimum distance open to the vision of the driver of a vehicle intending
to overtake slow moving vehicle ahead with safety against the traffic in
opposite direction is called overtaking sight distance

4. OVERTAKING REQUIRMENT
 The overtaking sight distance (OSD) is the distance measured along the centre
of the road which a driver with his eye level at 1.2 m above the road surface can
see an object 1.2 m above the road surface

5. FACTORS AFFECTING OSD
The factors that affect the OSD are:
 Velocities of the overtaking vehicle, overtaken vehicle and of the vehicle
coming in the opposite direction.
 Spacing between vehicles, which in-turn depends on the speed
 Skill and reaction time of the driver
 Rate of acceleration of overtaking vehicle
 Gradient of the road

6. ANALYSIS OF OSD (2 WAY ROAD)
 A vehicle (A) travelling at design speed v  desires to
overtake a slow moving vehicle B travelling at vb
 The vehicle A has to wait till he get an opportunity to
overtake B  accelerate , shift to the opposite lane and
complete the overtaking
 Return to the left lane without colliding with opposite
coming vehicle C
 Fig is shown in next slide

7. ANALYSIS OF OSD (2 WAY ROAD)

8. Overtaking may be split into 3 operations 
1) d1 is the distance travelled by the overtaking vehicle A during the
reaction time t of the driver from position A1 to A2 just before starting to
overtake B
2) d2 is the distance travelled by the overtaking vehicle A during the
actual overtaking operation during time T
3) d3 is the distance travelled by the vehicle coming in the opposite
direction (C) during the actual overtaking operation

9. Overtaking operation

10. Assumptions in analysis
 The overtaking vehicle is forced to reduce its speed from design speed to the
speed of overtaken vehicle (B ) & move behind it at a spacing s till an
opportunity for safe overtaking operation
 When driver of vehicle A finds a gap  decides within his reaction time (t) to
accelerate and overtake B  during this time vehicle A moves with a speed of
vb from A1 to A2 (d1)
 The vehicle A accelerate and overtake B within a distance d2  during time
interval T

11. Assumptions in analysis
 Distance d2 is split into 3 parts
 Spacing s between A2 and B1
 Distance b travelled by slow moving vehicle (B1 to B2)
 Spacing s between B2 and A3
 During overtaking time T, vehicle C in opposite lane travel from C1 to C2
through a distance of d3

12. Determination of components
 d1 = t * vb vb – velocity of slow moving vehicle
d1 = 2 vb t – reaction time ( t = 2 sec)
 d2= s + b + s s – spacing between vehicles (m)
d2 = 2s + b s = 0.7 vb + 6 metre
b = vb * T (T overtaking time)
(T= sqr {(4*s)/a} )
a – rate of acceleration
 d2 = vb * T + 2 (0.7 vb + 6)
 d3= vT T – overtaking time (sec)
v- design speed
If vb not given vb = v – 4.5 m/sec

13. OSD = d1 + d2 + d3

14. Rate of acceleration Vs speed

15. Overtaking zones
 It is not possible to construct the road with OSD at every point
 There may be stretches where overtaking is not possible
 However overtaking option should be given to vehicle moving at design
speed at frequent intervals as possible
 These zones are called overtaking zones
 The width of carriage way will be more at those zones
 Width and length should be sufficient for such zones for safe overtaking
DESIRABLE LENGTH OF OVERTAKING ZONE = 3 OSD
MINIMUM LENGTH OF OVERTAKING ZONE = 5 OSD

16. Overtaking zone

18. Overtaking zone
NON OVERTAKING

19. Intermediate sight distance
 If OSD cannot be provided  provide ISD
 ISD= 2 OSD
Head light sight distance
 The distance visible to a driver during night driving due to
head light
 HSD = SSD

20. Thank you
Lintels
For more…. Mail to aglaiaconnect2018@gmail.com