Transportation Engineering: Highways, Railways, Airports, Traffic Engineering
Coverage spans highway geometry and pavement design, railway track and alignment, airport runway length, and traffic flow theory. Numerical items come from superelevation, sight distance and delay; theory items from pavement layers and railway fixtures.
Core rules
- Superelevation e = V²/(127R), V in km/h and R in m; provide at most 7% (4% in urban areas), the rest being met by friction, and check the friction demand stays within about 0.15.
- Stopping sight distance = 0.278 V t + V²/(254 f), with t = 2.5 s and f ≈ 0.35.
- Overtaking sight distance uses a 2 s reaction time and considers traffic in both directions.
- Transition length from rate of change of centrifugal acceleration: Ls = 0.0215 V³/(CR), with C ≈ 80/(75 + V).
- IRC 37 pavement thickness is CBR-based; a 10 msa traffic with 5% subgrade CBR needs roughly 550 mm of granular crust.
- Railway cant e = GV²/(127R); cant deficiency is limited to 75 mm, or 85 mm above 100 km/h.
- Runway corrections: 7% per 300 m of elevation and 1% per 1 °C of reference temperature above standard.
Worked example
Design speed 80 km/h, radius 300 m. e = 80²/(127 × 300) = 0.168, i.e. 16.8%, far beyond the 7% limit. Provide 7% and let friction absorb the remainder: f = 0.168 − 0.07 = 0.098, below 0.15, so the curve is acceptable with 7% superelevation plus a transition.
Traps
Dropping the 0.278 in the SSD formula; substituting V in m/s into e = V²/(127R); applying the temperature correction before the elevation correction rather than after; and mixing PCU values across vehicle classes.