A transport file extension is related to the HP Printer Utility and used for its transport plugin files.
TRANSPORT file extension - HP Printer Utility transport plugin
What is transport file? How to open transport files?
File type specification:
The transport file extension is associated with the HP Printer Utility, a part of drivers for Hewlett-Packard printers, which enables users to configure them.
The .transport file stores transport plugin for Printer Utility.