Can you really make the traffic light green with a universal remote, and does it mess up the system?

Some can be change with quick blink of your headlights. Emergency vehicles have a device called an opticom which is a device that has a fast blinking strobe. The sensor near the light itself pick this up and gives you the green light. It doesn't mess anything up.

I've seen these devices on ebay but they were selling for close to $300 so be prepared to shell out some bucks for those green lights!

It’s easy. Almost any simple universal remote will work. All you have to do is program the code 911, and figure out which button sends the right frequency.