Now, I had gotten a clear view of the bus when it passed me, and the aisle was clear back of the accordion section:
And just to clarify, when I say "the aisle was clear", I mean "there was nobody standing up in the back 1/3 of the bus — the aisle was empty".
"There's plenty of room," I said to the driver, "people just need to move back."
"What am I supposed to do?" she asked with asperity. "I'm just one person."
You are the driver. You have more power in this situation than anybody else on the bus.
What are you supposed to do? You're supposed to put the bus in Park, stand up, turn around to face down the aisle, and announce in a loud, clear voice, "This bus will not move forward until everybody standing up moves back." And then follow through. Which I have witnessed bus drivers do.