Do Cargo fly very short routes?
It's fairly common for cargo, freight, and mail to be carried by aircraft - particularly for high value or priority cargo.

For example Royal Mail (the primary British mail service) uses short haul flights for distances of less than 100 miles (London Stansted to East Midlands Airport), along with around another 10 flights within the UK, every night.

These flights are used for priority (next day) mail, but will be filled with "cheaper" mail if necessary.

It all depends on the value of the cargo and the speed which it needs to travel, and aircraft only tend to be used where it is profitable to do so (ie where the cargo needs to travel fairly quickly and they can charge a high price to justify that).

Generally trucks will be used for shorter distances (&lt;500 miles) for low value cargo, and for longer distances for heavier cargo or cargo which does not need to travel quickly.

http://www.eastmidlandsairport.com/emacargo.nsf/content/customer_royalmail

https://en.wikipedia.org/wiki/Royal_Mail#Fleet