----x-----x-----S--------x--------U----------S/S---------x---------x-------B S is a speed limit; U is an uncoupler; S/S is a shunt signal and B is the buffers, all being operated from left to right. Without the speed limit in place, track circuits stop at the uncoupler with an approaching train until the time out triggers the shunt signal and track circuits then show up to the buffers. With the speed limit, the track circuits beyond the uncoupler show when the train passes the speed limit with the signal going off.