Poor doesn't mean there's a significant risk of collapse, but replacements can take years and the bridge is approaching its end of life without corrective action. Even bridges in critical condition can be used safely with proper monitoring, just not for very long.
https://en.wikipedia.org/wiki/National_Bridge_Inventory POOR CONDITION - advanced section loss, deterioration, spalling or scour.
SERIOUS CONDITION - loss of section, deterioration, spalling or scour have seriously affected primary structural components. Local failures are possible. Fatigue cracks in steel or shear cracks in concrete may be present.
CRITICAL CONDITION - advanced deterioration of primary structural elements. Fatigue cracks in steel or shear cracks in concrete may be present or scour may have removed substructure support. Unless the bridge is closely monitored, it may be necessary to close the bridge until corrective action is taken.
"IMMINENT" FAILURE CONDITION - major deterioration or section loss present in critical structural components or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to traffic but corrective action may put back in light service.