From Wiktionary: https://en.wiktionary.org/wiki/daraja
Could this also be a bike or a staircase ? As in Arabic... but maybe it doesn't. When words wander from one language to another sometimes some of the meanings get lost on the way and only a part of them survives...
Bicycle is baiskeli and staircase is ngazi. I think you're right that only one of the meanings crossed over into Swahili
Stairs/staircase is another meaning for daraja, but bicycle isn't.
My dictionary gives "degree, rank, or social station" as a third definition for "daraja". Interestingly it gives "steps" as the primary meaning, before "bridge".