Rebroadcasting in tunnels - how's it work?

[Scotty]

I had the UHF CB on in the car recently while driving through the Lane Cove Tunnel and was amazed to pick up transmissions on number of CB channels throughout the entire tunnel.

I assume the same system that is used to rebroadcast commercial radio inside the tunnel was also somehow rebroadcasting the CB, but always assumed that system would only cover the commercial radio bands.

Can anyone confirm how the tunnel rebroadcasting systems work, and would they cover the UHF CB band?