Скачать или смотреть Extra Widening in Highways – Formula, Calculation & IRC Standards for SSC JE, GATE, PSUs

📘 Topic: Extra Widening of Roads (Highway Engineering)
✅ Definition
Extra widening of pavement is the additional width provided on horizontal curves of roads to accommodate vehicle off-tracking and ease of maneuvering, especially for longer vehicles. It ensures safety, comfort, and reduces the chances of side friction between vehicles.

📌 Why is Extra Widening Needed?
On curved roads, two main factors require extra width:

Mechanical Widening – due to the off-tracking (rear wheels not following the front wheels).

Psychological Widening – due to the driver's tendency to feel uncomfortable on curves and need more lateral clearance.

🧠 Formula for Extra Widening
The total extra widening (Wₑ) is given by:

𝑊
𝑒
=
𝑊
𝑚
+
𝑊
𝑝
W
e
​
=W
m
​
+W
p
​

Where:

𝑊
𝑚
=
𝑛
⋅
𝑙
2
2
𝑅
W
m
​
=
2R
n⋅l
2

​
→ Mechanical Widening

𝑊
𝑝
=
𝑉
9.5
𝑅
W
p
​
=
9.5
R
​

V
​
→ Psychological Widening

📌 Parameters:

𝑛
n = Number of lanes

𝑙
l = Length of the vehicle (in meters)

𝑅
R = Radius of the curve (in meters)

𝑉
V = Design speed (in km/h)

🔍 Simplified Total Extra Widening Formula (IRC Recommendation)
𝑊
𝑒
=
𝑛
⋅
𝑙
2
2
𝑅
+
𝑉
9.5
𝑅
W
e
​
=
2R
n⋅l
2

​

9.5
R
​

V
​

✅ IRC: 73-1980 provides guidelines for widening on curves for different road classes.

📈 Important Points to Remember (Exam Tips)
Extra widening is not required on straight roads.

The larger the vehicle or speed, the more the extra widening required.

As radius decreases (sharper curves), widening increases.

For highway design, extra widening is critical at:

Horizontal curves

Intersections

Hairpin bends (especially in hilly roads)

💡 Numerical Example (SSC JE / GATE-type)
Q: Calculate extra widening for a two-lane road with design speed 65 kmph, curve radius 200 m, and vehicle length 6 m.

Solution:
Given:

𝑛
=
2
n=2,
𝑙
=
6
l=6 m,
𝑉
=
65
V=65 kmph,
𝑅
=
200
R=200 m

𝑊
𝑚
=
2
⋅
6
2
2
⋅
200
=
72
400
=
0.18
 
𝑚
W
m
​
=
2⋅200
2⋅6
2

​
=
400
72
​
=0.18m
𝑊
𝑝
=
65
9.5
200
≈
65
9.5
⋅
14.14
≈
65
134.33
≈
0.484
 
𝑚
W
p
​
=
9.5
200
​

65
​
≈
9.5⋅14.14
65
​
≈
134.33
65
​
≈0.484m
𝑊
𝑒
=
0.18
+
0.484
=
0.664
 
𝑚
W
e
​
=0.18+0.484=
0.664m
​

🏁 Use in Exams
Theory questions: SSC JE, RRB JE

Numerical questions: GATE, ESE Prelims

Design-based applications: PSUs (like BARC, ISRO, NHAI)

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Extra widening formula

IRC standards for highway widening

Mechanical vs psychological widening

SSC JE highway engineering questions

GATE civil engineering road design

PSU exam extra widening notes
Extra widening is a critical design aspect in highway engineering, ensuring safety and efficiency on curved roads. Mastering its formula, IRC standards, and calculations is essential for RB JE, SSC JE, ESE, GATE, and PSU exams.