Hephaestion

I had the same bug, massive drop in the number of public transport users as the city grew to 200k in size. However, I have successfully restored it to satisfying levels. I had a lot of custom industry vans (to replace the ugly donut trucks), but apparently their cargo capacity was set to a low value (3000) compared to the vanilla donut truck (8000). I conjecture that that this created swarms of vans which coupled with the agent limit reduced the citizen agenst. By changing the capcity to 12000 of all vans (using the advanced vehicle editor mod), and slashing the number of the commericial zones, I have restored both public transport and tourism to satisfying levels.

A cargo traffic jam :-)