The design speed for a two-lane road is 80 kmph. When a design vehicle with a wheelbase of 6.6 m is negotiating a horizontal curve on that road, the off-tracking is measured as 0.096 m. The required widening of carriageway of the two-lane road on the curve is approximately

Widening (We) = (nl^2 / 2R) + (v / 9.5 * sqrt(R)). Off-tracking is defined as l^2 / 2R. Given l = 6.6m and off-tracking = 0.096m, we have 6.6^2 / 2R = 0.096 => 43.56 / 2R = 0.096 => R = 226.875m. Mechanical widening = n * l^2 / 2R = 2 * 0.096 = 0.192m. Psychological widening = v / (9.5 * sqrt(R)) = 80 / (9.5 * sqrt(226.875)) = 80 / (9.5 * 15.06) = 80 / 143.07 = 0.559m. Total widening = 0.192 + 0.559 = 0.751m.