As part of the new system, I don't think very much at all, since the two technologies are fundamentally different; CBTC is trains talking directly to each other, and cab/wayside signalling is the tracks telling the trains what to do.
That being said, it's pretty common in retrofits for the older system to still be around as a fallback if the CBTC fails.
That being said, it's pretty common in retrofits for the older system to still be around as a fallback if the CBTC fails.