When you calculate the shortest path in a road network, you usually take the distance and divide it by the speed limit to determine the weight of the edges.
To be fancy you also do things like account for deceleration and acceleration at nodes (turns).
Artificially capping the speed limit is easy. You often do this for things like tractors that don't drive at the speed limit.
If people want to drive under a certain speed it's a trivial technical problems for the individual vehicle and path finding.
I'm not sure the calculations are made individually however, so an individual speed limit may be a non trivial problem
As you mentioned tractors, it's pretty sad one can't define usual/max driving speeds on Google Maps. Applies to e-bikes, tractors, cars with trailers, etc
To be fancy you also do things like account for deceleration and acceleration at nodes (turns).
Artificially capping the speed limit is easy. You often do this for things like tractors that don't drive at the speed limit.
If people want to drive under a certain speed it's a trivial technical problems for the individual vehicle and path finding.
I'm not sure the calculations are made individually however, so an individual speed limit may be a non trivial problem