A side-view road cutaway connects two tangent grades with a parabola. Watch a vehicle climb the changing slope while a driver-to-object sight line reveals where the road crest blocks visibility.
• 3D scene parts: Parabolic road profile; survey vehicle; entering and leaving tangents; driver-to-object sight line; horizontal station datum. • Controls: Curve length (80–400 m); Entering grade (-8–8 %); Leaving grade (-8–8 %); Vehicle speed (10–80 km/h); Object distance ahead (20–200 m). • Live readouts: Station from PVC (m); Elevation above PVC (m); Current tangent grade (%); PVT elevation (m); Visible distance within curve (m); Visibility minus stopping need (m). • Guided experiments: Crest curve; Sag curve; Constant grade. • Four tabs (visual laboratory, curves and measurements, experiments, learn and assess), a model-verification run, a timestamped event log and a trial report.
y(x)=g1 x+(g2−g1)x²/(2L) g(x)=g1+(g2−g1)x/L xext=−g1 L/(g2−g1), only if 0≤xext≤L Grades are decimal fractions. Crest sight bound S=√(2L/|g2−g1|)(√1.08+√0.60). Reported visibility is clipped at PVT. Stopping comparison uses 2.5 s reaction and 3.4 m/s² deceleration.
Geometric parabolic curve with exaggerated elevation. Eye/object visibility is limited to the displayed curve, without terrain beyond PVT. The stopping-distance comparison is illustrative, not compliance certification; suspension and drainage are omitted. Vehicle speed advances horizontal station; loops are a replay of the same traversal. Try the preset experiments, then compare the live readouts with the equations.
No. Grade varies linearly with station.
No. Both grades can have the same sign.
Geometric parabolic curve with exaggerated elevation. Eye/object visibility is limited to the displayed curve, without terrain beyond PVT. The stopping-distance comparison is illustrative, not compliance certification; suspension and drainage are omitted. Vehicle speed advances horizontal station; loops are a replay of the same traversal.