The description says that "flagstone, packed dirt, broken asphalt, fine floors, paved tiles and concrete" are considered roads. What about bridges? I find my pawns will often take a longer route instead of going over a bridge.
Even in other places it seems they sometimes go a rather circuitous route along paved roads instead of the quicker path I make for them.
If it matters, most of my roads are 2 cells wide of flagstone, though some I also put paved tiles on either side to make a total of 4 cells wide.