Possible Clues:

• Means of sending packages
• Bad place to cross river -- standard package travels this way
• One way to send a package
• Letters don't go this way by 6 across
• One way to send packages
• Never with the speed of 10 across and much bulkier (6, 4)
• Petrol cap's possibly something that comes with the van
• *Package-mailing option
• Port's place organised for goods transport system
• Method of shipping