What would be the extra widening required for a pavement of width 7 m on a horizontal curve of radius 180 m? The wheel base of the vehicle is 6 m and the design speed is 60 kmph.
- A0.370 m
- B0.470 m
- C0.570 m
- D0.670 mCorrect
Solution
Concept
Extra widening on horizontal pavement curves
Formula
We = nl2/(2R) + V/(9.5·√(R))
Step-by-step solution
1. Pavement width of 7 m corresponds to a two-lane road (n = 2). 2. Mechanical widening We = nl2 / (2R) = 2 × 62 / (2 × 180) = 0.20 m. 3. Psychological widening Wps = V / (9.5 × √(R)) = 60 / (9.5 × √(180)) = 0.270 m. 4. Total extra widening W = We + Wps = 0.20 + 0.270 = 0.470 m. Answer: D
Explanation
Extra widening on horizontal curves consists of mechanical widening based on vehicle wheelbase and psychological widening dependent on design speed. For a two-lane road of 7 m width with radius 180 m, mechanical widening equals 0.2 m and psychological widening equals approximately 0.47 m. Adding these values together yields a total extra widening of 0.67 m, which makes option D correct.
Why the other options are wrong
NONE
Shortcut
Total extra widening = Mechanical widening (nl² / 2R) + Psychological widening (V / 9.5√R).
Common mistake
Selecting option C by considering single-lane pavement (n=1) or option B by calculating only psychological widening.
Correct answer: D) 0.670 m