The truck's speed on the ramp is not animated — it comes out of a force balance used in real mine-haulage engineering (a rimpull–resistance diagram). Loaded and climbing:
θ = atan(grade/100)
F_roll = Crr·m·g·cosθ (rolling resistance)
F_grade = m·g·sinθ (grade resistance)
F_trac = min( μ·m·g·cosθ , P/v ) (traction- or power-limited rimpull)
a = (F_trac − F_roll − F_grade) / m
Heavier payload and steeper grade raise the resistance term; more engine power raises the power-limited rimpull curve P/v, but traction to the drive wheels (μ·m·g·cosθ) caps how much of it can actually be used at low speed — exactly the crossover that sizes real haul trucks.
Empty and descending, gravity supplies the driving force instead of the engine. Once the truck reaches the safe design speed for that grade, a retarder (not the engine) holds it there rather than letting it keep accelerating — the standard way declines are driven downhill.
The ramp is single-lane: with more than one truck sharing it, each direction pays a passing-bay wait at the midpoint proportional to (fleet size − 1), which is added directly into the cycle time and therefore the throughput.
- Speed–distance profile — orange for the loaded climb, blue for the empty descent; the flat blue segment is the retarder holding the safe descent speed.
- Net force — the current driving/resisting force on the truck; near zero once retarder or traction-limited cruise is reached.