You need to use the microcontroller approach. You're getting in way over your head. I don't say that with arrogance, but you're making this much harder than it has to be. Not to mention, a microcontroller or PLC would be better suited to this problem because that's what a real traffic controller would use, not a desktop PC's printer port. This project could be done on a Basic Stamp 2 in less than 30 minutes. Use the right tool for the job.