This feature can be disabled if the transport is run via the command line using the -U switch. More information can be found in the Operations Guide under the heading DBTransporterCMD.exe.
More information is provided in the Installation Guide, under Importing a transport package with the Database Transporter section.
As well as the Operations Guide, under Notes about importing transport packages.
As stated, "The database is set to single-user mode for the duration of the import. Close all existing connections to the database before starting the import."