Can "downstairs" in the phrase "From the street downstairs" be an adverb?

Vicki woke. Elizabeth was still sleeping, with her face to the wall. Her hair,
flattened in the night, had formed matted curls which reminded Vicki
against her will of what can be seen inside vacuum cleaners or the ripped
seat of railway carriages. From the street downstairs, out the raised-eyebrow
windows, rose a screeching of metal. Vicki slid out from under the
pink quilt and went to the window, but the tram had launched itself again
and was away, its little flag fluttering.

Does "street downstairs" mean: the rooms on the ground floor in a house. and "street downstairs" is another word for "ground floor"?

Or

Is "downstairs" here as an noun and "From the street downstairs" mean: from the downstairs that is towards street?

Can "downstairs" here be adverb?