Correct Answer - Option 3 : 0.75 m
Concept:
Off-tracking:
The phenomenon of the rear wheel not following the front wheels while negotiating the curve is called off-tracking. It depends on
- Length of wheelbase
- Turning angle or radius of the curve.
\({ off -tracking}\; = \;\frac{{{l^2}}}{{2R}}\)
The extra widening (We)of pavement is given by
We = Wm + Wp
Wm = Mechanical widening, Wp = physiological widening
Mechanical widening: The widening required to account for the off-tracking due to rigidity of wheelbase is known as Mechanical widening. It can be calculated as:
\({W_m} = \frac{{n{l^2}}}{{2R}}\)
n = Number of lanes
l = length of wheelbase = 6.1 m
R = Radius of circular curve
Psychological Widening: Extra width of pavement provided for psychological reasons such as overhangs of vehicles, greater clearance for crossing, etc is known as Psychological Widening.
\({W_{p}} = \frac{V}{{9.5\sqrt R }}\)
V = Design speed (kmph)
Calculation:
Given - l = 6.6 m, n = 2, V = 80 km/hr
off-tracking = 0.096 m
\({0.096}\; = \;\frac{{{6.6^2}}}{{2\times R}}\)
⇒ R = 226.875 m
\({{\rm{W}}_{\rm{e}}} = 2 \times 0.096 + \frac{{80}}{{9.5 \times \sqrt {226.875} }}\)
We = 0.752 m