[dongs]

Good day/afternoon/evening all
My motivation to reduce my carbon footprint has been growing, and with that comes the decision to try and drive less. I work full time and go to school part time. I'm about 4 miles from school and 15 miles from work. I've never been an avid biker but my hometown (Portland or) bills itself as being incredibly bike friendly, so I figure I live in a good place to start!
The ride to school is very easy, I live at about 500' and school is at ~100' or so. One hundred feet per mile to climb on a ride home doesn't sound too bad at all. Work on the other hand is a much greater distance, I've done some mapping and all the 'bike routes' send me way out of the way. The most direct route is along a major thoroughfare, it's the only diagonal street that breaks up the otherwise rigid grid system. A new bridge for public transit and bikes/pedestrians is opening soon, that would make for a much easier and safer crossing of the Willamette river.
Now on to the question. I don't currently own a bike. I've set a modest budget and intend to go to one of the many bike shops in town to see what's available used. I'm not sure if I should look for a street bike or a cruiser. My evening commute from work begins at 10pm and I'll most likely combine it with public transit to speed things along as well as increase my own personal safety. I work weekends and riding in the dark with possibly drunk drivers sharing the road with me isn't something I'm very interested in.
I'd like to get a bike that allows me to reach a reasonable speed with minimal effort. Road bikes look to be lighter but I suppose it all depends on the materials.
Thanks in advance!