🚧 Setback Distance in Highway Engineering – SSC JE, GATE, ESE, RRB JE & PSC AE Notes

Описание: 🚧 Setback Distance in Highway Engineering – SSC JE, GATE, ESE, RRB JE & PSC AE Notes
📍 What is Setback Distance?
Setback distance is the minimum lateral clearance required from the centerline of a road to an obstruction on a horizontal curve, ensuring that the driver has an unobstructed view of the road ahead to maintain Stopping Sight Distance (SSD).

It is a key concept in transportation and highway engineering and is frequently asked in RRB JE, SSC JE, GATE CE, ESE Civil, and PSC AE exams.

🛣️ Importance of Setback Distance in Road Design
Ensures safety by maintaining clear sight distance on horizontal curves

Prevents visual obstruction by trees, poles, buildings, or barriers

Affects road geometrics and horizontal alignment safety

📐 Formula for Setback Distance
Let:

𝑅
R = Radius of horizontal curve (in meters)

𝑆
𝑆
𝐷
SSD = Stopping Sight Distance (in meters)

The setback distance (m) is calculated by:

𝑚
=
𝑅
−
𝑅
2
−
(
𝑆
𝑆
𝐷
2
)
2
m=R−
R
2
−(
2
SSD
​
)
2

​

This formula is derived using geometry of a circular arc and line of sight.

🔢 Stopping Sight Distance (SSD) – IRC Recommended Values
Design Speed (km/h) SSD (meters)
30 30
40 45
50 60
60 80
80 120
100 180
As per IRC:66 and IRC:73 standards

🧠 Example Problem for GATE, SSC JE & ESE
Q: A horizontal curve has a radius of 200 m and SSD of 80 m. Find the required setback distance.

Solution:

𝑚
=
200
−
200
2
−
(
80
/
2
)
2
=
200
−
40000
−
1600
=
200
−
38400
m=200−
200
2
−(80/2)
2

​
=200−
40000−1600
​
=200−
38400
​

𝑚
≈
200
−
195.95
=
4.05
 meters
m≈200−195.95=
4.05 meters
​

📘 Frequently Asked in:
✅ SSC JE Civil Previous Year Questions
✅ GATE Civil Engineering Syllabus (Transportation Engineering)
✅ ESE Mains Conventional Paper
✅ RRB JE Civil CBT-2
✅ State PSC AE Civil Exams

📝 Quick Revision Points
Setback distance is critical only on horizontal curves

It ensures visibility equal to SSD

Affected by curve radius and sight distance

Frequently tested in objective and numerical problems

setback distance formula civil engineering

horizontal curve sight distance

highway engineering notes for SSC JE

transportation engineering GATE PYQs

civil engineering geometrics

stopping sight distance in curves
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