You can use dxf to bring the street network over, make sure the data is actually curves and not polygons (for streets). There's only linear segments supported atm, so any true curves need be segmented into some linear curves. Though don't segment them too dense, this may cause issues. Rather, in CE, use the graph cleanup tool and then set the street curvature again in CityEngine.
I've tried all the various curve flavours that I can find in maya but none of them seems to come through, have you tested this somehow ? If you have, can you tell me the steps that you took and the maya version / platform ?
ah, I forgot Maya does no more have a default dxf exporter as it used to have years ago.
you have to somehow export the lines to the formats .dxf ( or .osm or .shp or .gdb)
but there's an other way I'd take :
if you are familiar with MEL coding in Maya, you can create a MEL script which takes all your street center lines and produces the Python code for the street re-construction inside CityEngine. once this is set up, it's real easy to use.
are you familiar with MEL scripting ?
let me know. I'm REAL short on time atm, but I could help you somehow.