Transportation Engineering
Transportation Engineering covers highway geometric design, pavements, traffic engineering, and railway engineering. The exam tests IRC-based design formulas, pavement composition, and traffic-flow relationships.
Core rules
- Stopping sight distance: SSD = 0.278Vt + V²/(254f), with V in km/h, t in seconds, and f the longitudinal friction coefficient.
- Superelevation: e = V²/(127R); the maximum is generally 7% on plain and rolling terrain.
- A transition curve is provided to introduce superelevation gradually and to satisfy the rate of change of centrifugal acceleration.
- Flexible pavements distribute load through layers; rigid pavements carry load by slab action.
- Traffic flow: q = kV, where q is flow, k is density, and V is space-mean speed.
Worked example
For V = 80 km/h, t = 2.5 s, and f = 0.35: SSD = 0.278 × 80 × 2.5 + 80²/(254 × 0.35) = 55.6 + 72.0 = 127.6 m. The first term is the lag distance; the second is the braking distance. If the grade is significant, add or subtract the grade effect as required by the design standard.
Traps that cost marks
- Using 0.278 incorrectly or omitting the lag-distance term.
- Applying the same friction factor at all speeds; f decreases with speed.
- Exceeding the maximum superelevation without checking friction.
- Confusing PCU with vehicle count in traffic-capacity problems.
Exam focus
Memorise SSD, superelevation, and transition-curve formulas; know flexible versus rigid pavement layers and the CBR design approach.