I'm a new-comer to the world of radio's and I need some help. I'm in high-school and working on a senior project. Basically our idea is a safety system for automobiles that cuts out the car radio when there is an emergency vehicle in in the area and inserts an emergency broadcast. The device would be something as simple as a box that a civilian could stick in their trunk. The emergency vehicle would also have a transmitter. I actually have to build this so any information would be greatly appreciated. My main questions are, what frequencies would I use(public?), Where do I start, and how might I build this (kits?). Thanks in advance for any and all help.