155.910 is the car side of the "information" channel. Many years ago, all Sheriffs' Offices in Iowa had an "information" channel and an "operations" channel. "Operations" or "OPS" was a simplex channel. Some of them included 155.190, 155.010, 154.830 . . .
The "information" or "INFO" frequencies were half-duplex. That is to say you needed to monitor the base on one frequency and the cars on the other to get complete conversations. Some of the INFO base frequencies were 155.610, 155.310, 155.535 . . .
HOWEVER, the CAR side of INFO was ALWAYS 155.910, no matter what frequency the BASE side used.
Clear as mud? Let me know if you need clarification . . .
Scott
Rock Rapids
KBØULA