You can import lists of freight cars from a text file on your computer using the Import cars... menu item on the File menu; this can avoid some of the tedious typing if you have a list handy in another program or in a spreadsheet.
Create a text file with each freight car's reporting marks on a separate line. You can also include the freight car type on the same line separated from the reporting marks by a comma or tab. Here's an example file for importing:
SP&S 2001, XM SP 94844, GS SP 20756 WM 20012, XA