I love mass transit, and the Bay Area has quite a variety.  In San Francisco, they have MUNI: a system of busses, trolley cars, and trains to go about the city.  The trains, or muni-metro as they are called, come in two directions: inbound (toward downtown) or outbound (away from downtown).

At the metro stations they play two tones when a train approaches: low-high for the outbound train, and high-low for the inbound train.  It just so happens that the tones for the inbound train are a perfect fourth.  So, naturally, I start singing a little Petula Clark number (for the non-music geeks, the “downtown” in the song is a perfect fourth):

When you’re alone and life is making you lonely
You can always go inbound
When you’ve got worries, all the noise and the hurry
Seems to help, I know inbound
Just listen to the music of the traffic in the city
Linger on the sidewalk where the neon signs are pretty
How can you lose?…