Just a note about bidirectional, or "double-ended" as I learned it - this can be very useful (i read 30% speed-up) for City / National Road searches. One also

Just a note about bidirectional, or "double-ended" as I learned it - this can be very useful (i read 30% speed-up) for City / National Road searches. One also has multiple layers of roadways of varying arterial significance, allowing higher speed (lower weight) travel, with real-world roads. It was used at a mapping job to great boon by our backend.