@ Bob:

I agree that defining spatial characteristics is a challenge, but there actually is a large pool of resources already established for handling transit-related GIS issues. MPOs (metropolitan planning organizations, which are involved in regional transportation planning) often provide GIS support for transit agencies, as do county or State governments, universities and other educational institutions, etc. But I agree that it can be a challenge to track down the necessary resources, and there may be other regions or states that don't have the type of institutional support that we get here in Ithaca, NY.

The agency for which I work has an ArcGIS (ESRI) license, but I personally prefer Google Earth because it's better suited to my needs (i.e. looking up small batches of GPS coordinates).

@ Brian:

I haven't had any coffee yet today, but I still don't get the connection between the transit agencies you cited, Washington's transit agencies, and resource constraints that prevent agencies from joining Google Transit. But like I said, I'm not awake yet!

I'm glad to see that this has generated some interesting conversation. Thanks, all! Nicole