In next patch you can see new cargo chain - Mail

And we add special venicle only for this cargo:
5 trucks and 4 vagons

Also we will add 3 special truck station:
Big Post office (truck station)
Small cargo station(Bus station on the road, only unload)
Trash centre (truck station)

And yes, city will generate two cargo: waste and mail.

PS Sorry for my english ;)

http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1132613514
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1132193793