Input
Results
Approx. truck speed at top—
Speed reduction ΔV—
Truck flow on grade—
ΔV ≥ 15 kph?—
Truck flow ≥ 200 veh/hr?—
Climbing lane justified?—
Method
AASHTO speed-reduction curves give approx. truck speed loss vs grade × length. Approximation: ΔV ≈ grade × (1 + 0.005·L) (kph) capped at speed loss to 15 kph. Justification: (1) ΔV ≥ 15 kph AND (2) upgrade truck flow ≥ 200 veh/hr AND (3) LOS or capacity benefit.