A top-down haul-road model driven by three coupled real relations:
Drive: dv/dt = P·gas − c_r·v − g·sin(theta)·(1+load/cap)
Steer: dheading/dt = turn·grip/(1+|v|·k) (traction-limited)
Fuel: dF/dt = −(b0 + b1·|gas| + b2·load)/eff
Acceleration comes from engine power P against rolling resistance c_r·v and a grade penalty g·sin(theta) that scales with how heavy the truck currently is (1 + load/capacity) — a fully loaded truck struggles far more on an uphill grade than an empty one, exactly like a real haul truck.
Steering authority is traction-limited: turn rate falls off as speed rises (1/(1+|v|·k)), and the traction slider directly scales how much grip is available before the rear wheels start to slide wide on a fast corner.
Fuel burns from a base idle rate plus a throttle-proportional term plus a load-proportional term, all divided by the fuel-efficiency slider — hauling a heavier load at high throttle burns fuel measurably faster, and running dry stalls the engine until you refuel.
- Loader zone (green) — press Space here to fill up to the load-capacity limit.
- Crusher zone (orange) — hold Q to tip the bed, then press Space to dump.
- Grade readout — the live terrain slope under the truck, signed by uphill/downhill.