Sight Distance Are of Following Types

1. Stopping sight distance (SSD)

2. Safe overtaking distance (OSD)

3. Safe sight distance for entering into uncontrolled intersection

4. Intermediate sight distance (ISD)

5. Headlight side distance

QUESTION

Calculate the safe OSD for a design speed of 90 Kmph. Take the reaction time of the driver as 2.5 seconds and acceleration of the overtaking vehicle as 2.5 kmph/sec. Draw OSD Zone.

SOLUTION

Given data:

Design speed = 90 kmph 

Reaction time = 2.5 sec

Acceleration = 2.5 kmph/sec 

Solution: Consider the speed of the overtaking vehicle as the design speed (ie)

V= 90Kmph = 90/ 3.6 = 25 m/ sec V= vb=25 m/sec 

Acceleration a= 2.5 kmph/sec 

OSD= d1+d2+d3 

Reaction time (t) = 2.5 sec 

d1= vb t = 25x 2.5 = 62.5m 

S= [0.7Vb+b] =[ 0.7x 25x6] = 23.5 m 

Time T= square root 4X Vb

𝑎 =square root of 4X 25 /2.5

= 6.324 Sec = 6.3 

d2 = Vb T+2S = 25 x 6.3 + 2 x 23.5 = 104.5 m

d3 = 25x 6.3 = 157.5 m 

OSD = 62.5 +104.5 + 157.5 

OSD = 62.5 + 104.5 +157.5 OSD = 324.5 

OSD =325 m

QUESTION-

Explain the steps involved in the geometric design of hills roads

SOLUTION

Hill road is defined as the one which passes through a terrain with a cross slope of 25% or more. IRC: SP: 73-2015 and IRC: SP: 84-2014 have merged the Mountainous and Steep Terrain having Cross Slope more than 25%.