The small map size sucks balls, you can't make a mega city that does everything... From your screens looks like you can connection the side streets to the next map. I'll check this game out I think.
If you're talking about the thing on the left, that's a railroad track, which we can't do anything with in the beta. Just like the coastline where you could build docks and such eventually. They are, I think, just another outlet for us to generate more commerce, commuting, industry, etc. The main highway at the bottom is our only connection with other cities at the moment, even though when you zoom out the area around your dotted lines there are typically empty and would be great places to put more crap.
Very, very disappointed with the small size as well. I don't even know if it would be all that fun to build a bunch of small cities (as in, controlling a region yourself instead of leaving it up to chance who you get), each one specializing in something unique, because you'll just have pretty much the same overall layout minus a few specialization items I'd imagine. Also, I'd imagine the 3 cities per region is just for beta, but unless they increase that size dramatically you wouldn't even be able to do that much in a region you controlled all by yourself anyway.
I had fun, and definitely could have fun for hours at a time I'm sure, but I'm not sure I'll be buying it until it drops substantially in price unless I hear something that changes my outlook significantly.
EDIT: Oh yeah, and does anyone else get really annoyed by the "Sim voice"? I'd rather they were just silent (might be an option somewhere, but I'm not wasting my hour looking for it).