Included the Stopping sight distance, Overtaking sight distance, Intermediate sight distance and superelevation with equations

1. Welcome to Civil Genics...

2. Geometric Design of Highways
Concerned with; Cross sectional elements
Sight distance
Horizontal & Vertical alignment

3. Sight Distance
Visibility ahead to the driver at any instance.
- to stop – for safe overtaking – for entering to intersection
1. Stopping Sight Distance (SSD)
to bring vehicle to stop without causing hazard.
2. Overtaking Sight Distance (OSD)
to overtake without causing any collision.
3. Intersection Sight Distance (ISD)
to take control of vehicle and avoid collision while entering to a
uncontrolled intersection.

4. Stopping sight distance
Also called as non passing sight distance.
It depends; i. Brake efficiency – tendency to skid
ii. Frictional resistance – f = (0.35 – 0.4) as per IRC
iii. Speed of vehicle
iv. Gradient if any.
v. Total reaction time – 2.5 sec (in gen.)
Total reaction time = (perception time + brake reaction time)
perception time – time to understand the situation
brake reaction time – time to apply brake
based on ‘PIEV Theory’
Perception – Intellection – Emotion – Volition

5. Analysis of SSD
SSD = Lag distance + Braking distance
Braking distance can be found by equating work done for stop the vehicle and K.E. of
vehicle. { f*W*l = Wv2/2g }
SSD Design speed (km/hr)
90 65
120 80
180 100

6. Overtaking sight distance
IRC suggested the height of eye level of driver as 1.2m and height of object
as 0.15 above road surface.
Analysis;
Or,
OSD = 0.278vbt + 2s + 0.278vbT + 0.278vT
• Min. length of overtaking zone = 3*OSD and, Des. Length = 5*OSD

7. Crossing sight distance / intermediate sight distance
in sections where it is not possible to provide OSD.
CSD = 2*SSD
Sight distance at intersections
to stop, to change speed,
to cross main road etc.

8. Super elevation
transverse slope to the pavement surface at curves - to counter the
centrifugal force.
Super elevation, (e) = (Height of outer edge) / (Hor. Width)
where,
f – lateral friction factor
V – vel. of vehicle
R – Radius of curve
Generally we are taking emax = 0.07
and fmax = 0.15
So, by the equation
Allowable radius, R = 0.036v2
(In case of mixed traffic)

9. • Maximum value of super elevation;
Plain & rolling terrain = 0.07
Hill roads = 0.10
Urban roads = 0.04
• Negative super elevation indicates - no super elevation is required. There
Minimum super elevation equal to camber has to be provided.
• Raising of outer edge with respect to centre = (Be/2)
where B is the width of pavement
• Safe or allowable speed, v = (27.94R)1/2

10. Thank you..