Vertical Curve Design (Summit & Sag)

Computes required vertical curve length L and K-value for summit (crest) and sag curves using standard sight-distance formulas. S is typically SSD or OSD from your design.

Units & basic data

Current units: SI – gradients in %, lengths in metres.

Grade G₁% (e.g. +2.0)

Grade G₂% (e.g. −1.5)

Summit (crest) curve

Sight distance Sm

Eye height h₁1.08 m (default)

Object height h₂0.6 m (default)

Enter G₁, G₂ and S, then click Compute summit.

Sag curve (headlight control)

Sight distance Sm

Headlight height h_head0.75 m

Beam angle φdeg above road (≈1°)

Enter G₁, G₂ and S, then click Compute sag.