Transportation Engineering
Transportation Engineering covers highway geometric and pavement design, traffic flow, railways and airport planning.
Core rules
- Stopping sight distance: SSD = 0.278Vt + V²/(254f), with V in km/h, t in seconds and f the longitudinal friction factor.
- Superelevation: e + f = V²/(127R); IRC limits maximum e and provides friction for mixed traffic.
- Flexible pavement design is based on CBR and design traffic in standard axles; rigid pavement design uses slab stresses and temperature gradients.
- Traffic flow: q = k × v, where q is flow, k density and v space-mean speed.
- PCU converts mixed traffic into equivalent passenger-car units.
- Railway: cant e = GV²/(127R); equilibrium cant balances centrifugal force.
Worked example
Find SSD on a level road for V = 80 km/h, reaction time t = 2.5 s and f = 0.35. Reaction distance = 0.278 × 80 × 2.5 = 55.6 m. Braking distance = 80²/(254 × 0.35) = 6400/88.9 = 72.0 m. SSD = 55.6 + 72.0 = 127.6 m. If the road has a gradient, the braking-distance term is modified, so the level-road value is not simply reused.
Traps
Using V in m/s in the 0.278 formula; omitting reaction distance; using a friction factor that assumes a different design speed; confusing PCU with actual vehicle count; using CBR as a strength parameter for rigid pavement.