This site may give you some assistance.
The "break" or "breaker" request isn't mandatory, it's a courtesy. Most radio users keep their radio squelched down to limit static. Only problem with this is that there may be radio traffic on the channel that you can't hear because it's not quite strong enough to break your squelch. A "break" request is a courtesy so you just don't run over another user's communications.
Though truck driver's have no legal exclusivity to channel 19, I would suggest that you respect their use of it. Cell phones have pretty much made CBs obsolete in passenger vehicles with the exception of truck drivers. Should you ever find yourself needing to use your CB to get help, most likely it will be a truck driver who responds.
Channel 9 is reserved by the FCC for emergencies or traveler assistance.
Used to be that I had a CB in every vehicle I owned. Now, I have several of the handheld FRS/GMRS radios that we use for communications while traveling in a group. Kind of miss the CBs though.
Hoss