Camber elevations at 320.50 m

Data

Centre line RL = 320.5 m, camber = 2.5% (1 in 40), two-lane carriageway, lane width = 3.5 m so pavement width $B=7$ m (half-width 3.5 m), shoulder width = 1.5 m with cross-slope 5%. Distances are measured from the centre line: centre of lane at $x=1.75$ m, pavement edge at $x=3.5$ m, road edge (shoulder edge) at $x=5$ m.

(i) Straight-line camber

Fall $=c\,x$.

• Centre of lane: $320.5-0.025(1.75)=\mathbf{320.456}$ m
• Edge of pavement: $320.5-0.025(3.5)=\mathbf{320.413}$ m
• Road edge (shoulder): $320.413-0.05(1.5)=\mathbf{320.338}$ m

(ii) Parabolic camber

Parabola with crown at the centre line: $y=\dfrac{2c\,x^2}{B}$ (so the total fall at the edge, $x=B/2$, is the same, $cB/2=0.0875$ m).

• Centre of lane ($x=1.75$): $y=\dfrac{2(0.025)(1.75)^2}{7}=0.02188$ m, RL $=\mathbf{320.478}$ m
• Edge of pavement ($x=3.5$): $y=0.08750$ m, RL $=\mathbf{320.413}$ m
• Road edge: $320.413-0.05(1.5)=\mathbf{320.338}$ m

The parabolic camber keeps the middle of the pavement flatter (better riding) and is steeper near the edges, which helps drainage.