Transportation Engineering
Transportation engineering covers highway geometric design, pavement materials and design, traffic engineering, railways and bridges. BTSC JE questions emphasise IRC standards, sight distance, superelevation, CBR and pavement layers.
Core rules
- Stopping sight distance SSD = vt + v²/(2gf), with v in m/s; reaction time t is usually 2 s.
- Superelevation e = V²/(127R) with V in km/h; IRC limits it to 7% for plain terrain and 10% for hilly roads without snow.
- CBR is the ratio of penetration resistance of a soaked sample to that of standard crushed stone; flexible pavement thickness is designed from CBR.
- Flexible pavement layers: subgrade, sub-base, base and wearing course; rigid pavement transfers load by slab action.
- Railway gauges in India: broad 1676 mm, standard 1435 mm, metre 1000 mm, narrow 762 mm.
Worked example
Design SSD for V = 80 km/h, t = 2 s, f = 0.35. Convert v = 80/3.6 = 22.22 m/s. Lag distance = 22.22 × 2 = 44.44 m. Braking distance = 22.22²/(2 × 0.35 × 9.81) = 493.8/6.867 = 71.9 m. SSD = 44.4 + 71.9 = 116.3 m. Using 80 directly in the braking term would produce an absurd result.
Traps
Using km/h in the braking formula; applying the 7% superelevation limit to hilly terrain; confusing SSD with overtaking sight distance; forgetting CBR is measured on a soaked sample; mixing formation width and carriageway width.