In the 80s I believe they used 87xx numbers and operated on the same frequencies as the rest of NSP, so I doubt the frequencies have shifted but I haven't heard 87xx numbers in sometime. With the new system coming to all over Nebraska they may end up with their own talk group.
They operate on 42.34 just like the rest of the troopers. In the 70's & 80's, Carrier Enforcement Officers operated on 39.9 mHz. They were not NLETC certified, were not armed (although they were given State Deputy Sheriff authority to write citations) and were a division of the Nebraska Department of Roads. They were merged with the State Patrol several years ago and are now trained as troopers. The Liquor Control Commision Agents were merged about the same time and they too have the title of "trooper."
Even back in the 70s and 80s Carrier Enforcement had access to NSP radio. The Warden of the Penitentary has access to NSP in his state issued vehicle, and this is a little known fact. How do I know? I used to work at the Pen and discovered the extra radio while driving the Warden's car one day on assignment. Further as I recall, the Deputy Warden and the Major of the Pen also have or had access to NSP radio in their issued vehicles.
Nebraska Department of Roads Carrier Enforcement Officer "Red" Hall who worked the A-Troop area in the 70's & 80's only had a 39.9 Motrac and a Plectron monitor on 42.46 mHz. in his cruiser. His primary communication points of contact were with the Cass, Sarpy and Douglas County Sheriff Departments on 39.9 mHz. Red was a unique character who had the ability to know if a truck was overweight just by hearing the noise from the tires of a passing rig. He never missed.
If NSP Omaha needed to contact him, they would usually just telephone the Douglas County Sheriff and the dispatcher would relay the traffic to him on 39.9
The NDOR Carrier Enforcement Officers at the Greenwood scales also had 39.9 radios and they communicated primarily with Ashland, Wahoo, Plattsmouth and Papillion. NSP was very touchy about who transmitted on their frequencies back in the good old days.