jass said:
Many other cities (like San Francisco) user color to differentiate lines, instead of letters (or both).
The reason: People associate the letter branches with westbound trains. Having an F train go the other way = confusing.
The problem with that is we already have a color coded system so if you have 2 red lines it would be even more confusing.
I am willing to be that people only associate the letters with westbound trains because there is no service from the north (Lechmere, yes, but most people wouldn't think of Lechmere if you asked them about the Green Line).
Don't get me wrong, I do think that the Green Line needs a better system, and I do think that SF is a great example of how that would work. The only problem then is it wouldn't be the 'Green' Line.