Original ETA is what the trip plan calculates as the ETA when the trip is initiated. This is also referred to as Scheduled ETA. It is based off of a trip plan which is set from a historical trip that is cleaned up (corrected for delays, bad orders diversions, etc). Once this trip plan is set, it does not get automatically changed based on weather, curfews, etc.
Required Delivery Date (same as Confirmed Delivery Date) is the date that was promised to the customer from their ERP system, if it was entered into the BOL. Most customers do not send this out, so we make up an RDD by adding two days to the original ETA. (This becomes a means of differentiating cars that are within 2 days of expected transit vs. those that are delayed further.)
Current ETA is dynamically revised while the car is in transit with every new CLM (or even the absence of an expected event).
If the Current ETA exceeds the RDD, then the car is considered to be IN DANGER.