I've tried it and figured it out. You can assign a bonus to your trade routes as a percentage of the standard commerce you get from them. This bonus can be in , , or again. So, you can have a trait with +50% on , but this looks slightly different in-game; I'll try and explain: # Your trait is described (I think) as "+50 on ", note the lack of a percentage sign. # In your city viewer, the value for your trade route yield is boosted appropriately, but when you hover over the value the description is now wrong. Say your trade route is worth 2 ordinarily, boosted to 3 ; the hovering explanation which appears will explain how it is worth 2 , but will not mention the +50% you get added on for your trait. Things get even more interesting if you assign a food or hammer bonus to trade route yield. A late-game trade route generating 8 but with a 25% bonus for trade routes would give you 2 on top of 8 . Sweet! I'm now trying to figure out if Industrious would work well with a percentage bonus on trade routes. This would solve the initial problem of my Ind being far too powerful early game with the original "+1 on 3 (or 4) ", and would get rid of what I now think is an annoying feature - having to choose your tile upgrades specifically to hit a threshold. Is it fair to say that a late-game (coastal, free market, corporation etc) city would generate between around 12 and 30 commerce from trade routes? If so, then 20% of this in wouldn't be overpowering would it? So that's a total (I'm fairly sure that the bonus yield takes into account the trade route total rather than each individual trade route being eligible for a boost) of +2 in a late game small city, and +6 in a late-game powerhouse. Thoughts?