450-451 and 455-456 are used for TV and radio STLs, studio transmitter links. BSI, broadcast sports intl, contracts with the IRL to provide wireless mics and cameras.
You will hear program audio, which is what TV or radio listeners hear, which is used so the pit announcers can hear the booth and each other to keep track of what is going on.
Some of these freqs have interrupt, which is where the producer talks to announcers to have them ask a question or give the announcer his queue to go to break or pass off to another announcer.
Camera PL, or program loop, is interfaced into the truck's intercom system so the pit camera operators hear the same thing as fixed cameras around the track.
When I did the radios for the teams most did not have repeaters so their range was pretty short, only 4 watts with an antenna about a foot off the ground.