[bee_rider]

Please forgive me for the ignorance, but is there some significance of “under the bay bridge” for this study, or did they just pick it arbitrarily? It seems like picking a point arbitrarily like that could introduce some skews.

[Me1000]

I'm pretty sure it's just being used as a turn of phrase here. Under the bridge means commuters are riding BART, over the bridge means they're driving.