Today the B903 provides a link from the A904 to the village of Blackness on the Forth Coast, ending on an unclassified road at a junction in the village, just out of sight of the firth. However, this is not the original route of the road.
In 1922 when the number was first allocated, the B903 was a little to the south, running from Linlithgow to Champany, where it ended on the then-B902. By 1932 the route had been extended to Blackness. Later, the A9 through Linlithgow was downgraded with the construction of the parallel M9. As such the A803 was extended through Linlithgow along the original section of the B903, meeting the motorway en route, and thus truncating the B903 back to its extension.