Factorio's Rail pathfinder is A* with various penalties to the distances based on entities attached to the rail, and trains on the rail. This mod allows adjusting these weights.

The pathfinder first builds a list of non-disabled stops that match the name in the schedule, then searches outward from both ends of the train at once, if applicable, in segments. A segment is an uninterrupted plain sequence of rails, with no intersections, stops, or signals (all of which define segment borders). The base distance for a segment is it's length (linear grid length along the center of the rail), which is then adjusted as follows:

• A segment ending in a circuit-closed signal is lengthened by adding Signal Reserved By Circuit Network Penalty
• A segment in a currently-occupied block is lengthened by adding (2*length)/(1+distance of block from start)
• A segment starting or ending with stops is lengthened by adding Train Stop Penalty
• A segment which is in a new block along the path that has a train in it is lengthened by:
  • Stopped Manually Controlled Train Penalty
  • Stopped Manually Controlled Train Without Passenger Penalty
  • Train In Station Penalty, and additionally Train In Station With No Other Valid Stops In Schedule if applicable
  • Train Arriving To Station Penalty
  • Train Arriving To Signal Penalty
  • Train Waiting At Signal Penalty + Train Waiting At Signal Tick Multiplier Penalty