Work out trip distribution (gravity model) instantly with clear inputs, formula shown and shareable results.
The gravity model distributes trips from an origin in proportion to each destination's attraction weighted by a friction factor that falls with travel cost. Comparing the weighted share with the raw attraction share shows how much the impedance term shifts trips: a nearby zone captures more than its size alone would suggest.
Gravity model
Tij = Pi x (Aj Fij) / sum over all j of (Aj Fij)
Tij = Pi x (Aj Fij) / sum over all j of (Aj Fij). The gravity model distributes trips from an origin in proportion to each destination's attraction weighted by a friction factor that falls with travel cost.
Commonly an inverse power or negative exponential of travel time, calibrated so the modelled trip length distribution matches observed data.
This calculator takes 4 inputs: Trips produced by the origin zone, Attraction of the destination zone, Total attraction of all zones, Friction factor for this pair. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.