Ok, you need two different building (can't remenber the names, A is origin, B is destination) in order to create a road. Once you unlock your first road it appear in the building list.

Be aware that longer is better. And that having luxuries in both start and end of the road will give you extra of these luxuries.

A road is created between each A and B. So if you have 2 A and 4 B you get 8 roads.

Be aware that if longer is better, it's also harder to protect the road (any system on the road on blockade will cancel the road until end of blockade not sure if the road take another path if it could).

You add all the B of AI with trade agrement, so it worth it to make peace and get a trade agreement if it's possible.

You also have some tech/building/hero traits that increase the yield of roads (+X% of dust/luxuries). Usefull to build in A and B system, not sure about the system on the way. Those building have a 32dust upkeep but worth 10 time this (and maybe more)

And you can spend dust to upgrade road (you buy ships for the road, check the economy screen)

Road level up, the more road you have the faster the level up is. At some point it's snowball.

That's pretty much all I know about trade roads. In my games road end to give me 99% of my income with huge numbers.

Currently they are way too overpowerd imho. I have had 1 million dust income per turn around turn 55 on fast.  (won economic victory t61 on endless)

I have yet to give them a serious try, but yes at first glance I saw it as somekind of exponantial income. Considering your experience Eysteinh your feedback seems to confirm it.

As you are with the VIP team, do you know if dev are aware of the issue?