There are many threads on doing passenger car lighting with the strips and various regulator solutions, both home-rolled and off-the-shelf solutions. I came up with the LED lighting regulator board to make the job of LED lighting a passenger car easy.
LED Lighting Regulator
The module gives you DCS compatibility, flicker free operation, adjustable intensity, and of course, low power operation. You can get 5 meter reels of LED's in amber, warm white, or bright white, for $3-4 from a host of places. One reel will do eleven 18" passenger cars or ten 21" passenger cars. Obviously, shorter cars work as well, you just get more cars from one reel of LED's.
As mentioned, I also packaged a solder-free kit, obviously it costs more for each car as I had to do the packaging.
Passenger Car LED Lighting Kit
For anyone that can do basic soldering, the modules are a much more cost effective solution.