Conditional Concatenated List

Hi all,

I have a highway junction with 3 arms. Each arm has an ID (1A, 1B, 1C).
I have the bus services that approach the junction from each arm.
I then have a table of interventions (say, new bus lanes on some of the arms), each affecting a different combination of the junction's arms.
I'd like, for each intervention, the list of bus services affected, using the most basic formula possible.

An example spreadsheet is provided. The yellow table is the expected result that I'd like formulas to calculate. [edit, apologies for the error in the 2nd row, hopefully you get the idea!]

Thanks for your ideas.

That's excellent, thanks Ali