you mean one RSL ?
One FR call (or 2 HR calls, or 1 SDCCH) generates about 0.4kb/s of signalling (that’s the SACCH net bitrate)
One RSL is dedicated for 1 TRX (= 8 timeslots)
8 FR calls, or 16 HR calls, or 8 SDCCH timeslots generate a minimum throughput of:
8 * 0.4 kb/s = 3.2kb/s
1 RSL is usually located on a quarter of an ABIS timeslot, i.e. 16kb/s. Even at 40% loading, that’s more than enough to carry all the signalling for all the possible traffic.