Trade vehicles on the campaign map

I was just testing my new campaign map, and I noticed trade carts moving along some of the roads - only the ones between Senate faction provinces. Has anyone seen this before, because I certainly have not. They do not seem to have any effect on the game. I would post a screenshot if I knew how to take one. If anyone has seen this before, do they know why these models show up?

Thanks,

~Prince Laridus Konivaich

They show up to indicate trade. More carts indicate more trade. Little ships traveling along sea routes serve a similar function.

-Simetrical

I just found them strange because I have never seen them on the Imperial campaign. The other thing is that there are no trade resources in description_regions.txt for my map! So there really should not be any trade going on!