Surveying
Surveying
Surveying
Reaction time of a driver is the time taken from the instant the
object is visible to the driver to the instant when the brakes are
applied. Many of the studies shows that drivers require about 1.5
to 2 secs under normal conditions. However, taking into
consideration the variability of driver characteristics, a higher
value is normally used in design. As suggests a reaction time of
2.5 secs will be use.
SIGHT DISTANCES
The speed of the vehicle very much affects the sight distance.
Higher the speed, more time will be required to stop the vehicle.
Hence it is evident that, as the speed increases, sight distance also
increases.
• Efficiency of brakes
The efficiency of the brakes depends upon the age of the vehicle,
vehicle characteristics etc. If the brake efficiency is 100%, the
vehicle will stop the moment the brakes are applied. But practically,
it is not possible to achieve 100% brake efficiency. Therefore the
sight distance required will be more when the efficiency of brakes
are less. Also for safe geometric design, we assume that the
vehicles have only 50% brake efficiency.
SIGHT DISTANCES
• Frictional resistance between the tyre and the road
Gradient of the road also affects the sight distance. While climbing
up a gradient, the vehicle can stop immediately. Therefore sight
distance required is less. While descending a gradient, gravity also
comes into action and more time will be required to stop the
vehicle. Sight distance required will be more in this case.
SAFE STOPPING SIGHT
DISTANCE
Vt D
S = Vt + D
N =W
+G -G
SAFE STOPPING
DISTANCE
When: h1 = 1.14 m
h2 = 0.15 m
L = in meters
S = in meters
A = g1 – g2
STOPPING SIGHT DISTANCE (on Vertical
Curves)
A. When S < L
When: h1 = h2 = h
STOPPING SIGHT DISTANCE (on Vertical
Curves)
A. When S > L
When: h1 = 1.14 m
h2 = 0.15 m
L = in meters
S = in meters
A = g1 – g2
STOPPING SIGHT DISTANCE (on Vertical
Curves)
A. When S > L
When: h1 = h2 = h
Problem 5: