I think you need to have training annually or biannually if you have a hazmat endorsement. And fleet drivers are all required to have one. I don't know about dedicated.
We had an outside carrier get unloaded this morning, make it all the way back around to the outbound gate, and when he went to pull off, dropped his trailer. When asked what happened he said, i dont know. I said i know what happened. Complacency.
Every circumstance is different, and sometimes it's beyond driver control. In a previous job I worked at we pulled the same trailer day in and day out. Never unhooked. We had a driver leave a steel mill in Gary IN and while driving on the overpass on to Cline Ave (912) the trailer uncoupled and dropped to the pavement. Of course everyone claimed driver error, not hooked correctly, after shop serviced his trailer blah, blah, etc. Funny how this driver left our terminal, drove 1500 miles previously during the week, and everything was fine until now.