Streetscapes: Who causes traffic?

Hint: not bikes or buses.

Not buses ... (Chelsea Street, Charlestown)

Not bikes ... (Route 99, Everett)

Not people ... (Essex Str, Chinatown)  [note the useless bus lane]

(I-93 tunnel approach)

Well, you get the idea. The occupants of all these cars could easily fit in one bus. Sadly they create traffic instead.