I'm in the midst of a light rail obsession. Think modern streetcars like in Portland, Atlanta, Edinburgh, Dubai. I'm trying to find a good book on the modern stuff and a source for HO or N equipment.
I definitely like the Kato Portram and Centram models as an out of the box reliable approach. There does seem to be a dearth of information on modern streetcar operations.
Most of it is pretty straight forward. There was an article in the Oct 1989 Model Railroader on the San Diego Trolley that covered the construction and whatnot, along with drawings of the cars. Operations would be the easiest with decoders and transponding. I had at one point kicked around the idea of an light rail layout with a shortline using the rails to serve customers in different parts of the city. Using the newer decoders, it would be possible to use JMRI to automate the running of the LRV's on a schedule and run the freight in between the cars.
You're not going to find much in RTR LRVs these days. But here's one company that makes resin body kits for light rail vehicles: http://ihphobby.tripod.com/
Calgary,Edmonton, San Diago and others use Siemens/Duwag cars. Calgary recently ordered 60 S-200 cars from Siemens, which are being built in North America.
This is an interesting subject. For me, I try to ride the light rails when I am in a city that has them. So far, I have been on rides in Atlanta, St. Louis, Denver, Dallas, Disney World, Minneapolis and Las Vegas. It is cool and you get to meet interesting people. Another interesting facet of the light rails is they ride high above neighborhoods, then they run underground in the city like a subway (in some cities). Good luck with your project.
I think there are obstacles to modeling many light rail systems in any scale, starting with the difficulty of modifying or obtaining existing models to look like US prototypes. The Kato Portrams have the immediate disadvantage that they're set up for left-hand running (Japanese style), and also for low-level curbside loading, where newer US systems are set up with doors on both sides for high level loading. Something like the recent Breda cars in Los Angeles would be a major kitbash from the Katos:
