Roads, Bridges and Transportation Engineering
Expect classification of roads and bridges, cross-section elements such as camber and gradient, flexible versus rigid pavements, and a few railway items such as gauges and signals.
Roads
- Indian classification: National Highways, State Highways, Major District Roads, Other District Roads and Village Roads.
- Cross-section: carriageway, shoulders, kerb, camber, side drains. A two-lane carriageway is about 7.0 m wide with 1.5 m shoulders.
- Camber drains rain from the surface: about 2–3% for bituminous and 1.7–2% for cement concrete surfaces. Gradient is the longitudinal slope; superelevation is the cross-fall on a curve.
Pavements
- Flexible pavement layers: subgrade, sub-base, base course and wearing course - load spreads gradually.
- Rigid pavement is a cement concrete slab with expansion, contraction and warping joints; it carries load largely by slab action.
Bridges and railways
- Components: foundation, abutment (end support retaining the earth), pier (intermediate support), bearings, deck or superstructure, railing and wing walls.
- A culvert has span up to about 6 m; minor bridges roughly 8–30 m; major bridges above 30 m.
- Railway gauges: broad 1676 mm, metre 1000 mm, narrow 762 mm.
Worked example
A 7 m carriageway is given a 2% camber. The crown is at the centre, so the half-width is 3.5 m and the rise at the crown = 0.02 × 3.5 = 0.07 m = 70 mm. Doubling the camber to 4% would give 140 mm, which is too steep for fast traffic.
Marks-losing traps
- Mixing camber (cross slope) with gradient (longitudinal slope).
- Saying flexible pavements need expansion joints - that is rigid pavement.
- Confusing pier (intermediate) with abutment (end).