It is assigned by the manufacturer. You can find the GVWR on the VIN plate on the door or door frame of most power vehicles, and on the VIN plate on most trailers. If you add the GVWR from the Truck and trailer and it is more than 10,000 pounds, it's a commercial vehicle. For example, a Ford F150 has a GVWR around 7000 pounds by itself. A tandem axle flat bed trailer usually has a GVWR of 7000 pounds.
NJ Transit trains travel at different speeds depending on the line, express or non-express, and weather conditions. ! The NJ Transit train travels over 90 miles an hour. Just like the speed of lightening !
Instead of taking the Amtrak all the way through to Newark, I would get off in NYC and take the NJ Transit train into NJ. Amtrak stops at Penn Station and the NJ Transit train also stops at Penn Station. Hopefully you won't have big pieces of luggage with you. Have your family pick you up at the nearest train station. Taxi fare from Newark Penn Station to Saddle Brook will probably run you $75+.