The B9109 is a short link from the A904 into Blackness on the northern edge of West Lothian. The road was originally unclassified but had gained its number by 1932.
The road starts at a simple T-junction at the western end of the parkland surrounding the estate of The Binns, now owned by the NTS, and heads north along the edge of the park. It then drops down the hill across the Black Burn and ends less than a mile later on the B903. Turning right here leads down to Blackness and its famous castle jutting out into the Forth, whilst left leads back to the A904.