I just renewed mine at the Chicago passport office. I know the CPO will provide you with an expedite letter to submit with your renewal, but I did not obtain one. I did take my United ID, and they used that as basis to expedite my application for a same-day renewal. I dropped everything off in the morning and picked up my new passport at 3pm. I submitted an expense report for parking and an hour of add-pay for having to show up to the passport office in person. Everything was approved, even the add-pay. Everyone at the passport office was super nice, and I dare say my experience was actually pleasant.