Arterials leaving the centre (0 = from the size class).
How far beyond the radius arterials reach (multiple of the radius).
Longest stretch of water a bridge may span, metres (0 = no bridges).
Steepest grade a road segment may climb (rise / run) before it is steered or pruned.
Hard cap on growth steps (keeps huge settings bounded).
Smallest angle between two roads at a junction, degrees.
Local streets.
Arterial roads.
Surfaces of roads through farmland (used where worse than the settlement's own).
Collector roads.
Road ends within this distance of a junction or road join it, metres.
Speed multiplier per surface (cobbles and dirt are slow).
Lanes per direction and speed limit (m/s) per class, for vehicles.
Gravel and dirt roads are this much narrower (fraction of the class width).
Road network rules (Parish & Müller 2001 global goals + local constraints).