I think you tried using the wrong tool. Nano Banana is for editing, not generating (there's Imagen for that).

Imagen4 did no better. edit: example https://imgur.com/Dl8PWgm with a so-so result: four lanes, cars at least facing the same way, lane block looks good, weird extra division in the center, some numbers repeated, one arrow going straight into construction, one arrow going backwards

edit: or Imagen4 Ultra. https://imgur.com/a/xr2ElXj cars facing opposite directions within a lane, 2-way (4 lanes total), double-ended arrows, confused disaster. pretty though.