Trade Routes are gone. I keep meaning to write a civilopedia article on it, but basically it has been replaced with a much simpler concept.
Instead of trade routes, you have connected cities. This is what is shown where trade routes used to be, in the top left of the city screen. Certain buildings give commerce from having connected cities. Certain civics may increase or decrease the commerce from connected cities. Connectedness is similar to trade routes in that you must have a path (either road or ocean) to have the game consider a city connected. But the differences are that by default, you earn nothing from connected cities, and certain buildings provide a flat
bonus. See the port building for an example of this.
I wrote up a lengthy rationale for the change many months ago, but the distilled version is this: Trade Routes were hard to understand, it was impossible to predict the effects, and finally, bad for game performance in the late game. This trifecta, of complexity, unpredictability, and slowness caused us to look into a system to replace Trade Routes. Connected Cities is this system. In contrast, connected cities are easy to understand, as connected cities are listed in your city screen (and paths are pretty obvious to see visually), easy to predict the effects, as long as you are capable of counting, and simple to calculate.