At Pasco, on the NP and early BN, it was the retarder operator! The mainline was considered "within yard limits". so the yard controlled access. And, as the person with the control panel, that meant the retarder operator.
Further south, in town, everything was controlled by the operator at the depot, which included the Columbia River bridge, the NP/SP&S junction and wye, access to the roundhouse/service area, and traffic north to the south end of the hump yard tracks.