Because, as Stephanie reports, it just ran out of fuel. How does that happen?
Happened to me on the 50 once -- luckily only a few blocks from Forest Hills.
And notice the wide space between the bus and the curb at the bus stop. Had the driver pulled up to the stop like they're supposed to, a lane of traffic wouldn't be blocked by the bus. This is all sounding familiar...
To be specific, the driver has stopped just to the left of their clearly marked bus stop space. I commute daily on the 66, and this is a constant problem, in many cases (like this one) without even the excuse that they are blocked in some way from pulling up to the curb.
BTW, I have many times seen bicyclists pass buses that are stopped this far from the curb on the right, even as the buses are discharging passengers - a confluence of two evil and illegal behaviors. (Yes, yes, I know - it's LEEEGALLL for bicyclists to pass traffic on the right, apparently even when it's dangerous in every way to do so. This past Monday morning I watched a cyclist squeeze between my bus, stopped at a light, and the parked lane of cars, through a space so narrow he couldn't actually pedal the bike - he was touching both the bus and the car as he eked his way through. But is it legal for ANY vehicle of ANY kind to pass a streetcar or bus on the right while it's discharging and taking on passengers? I don't think so...)
It's easy to run out of gas when it's the 66, it spends more time idling in traffic then it does actually moving.
I know that the RTS buses do not have fuel gauges, and it is quite likely that the NABIs don't either.