When people look at the 3-way prefab they actually see how the roads cross in very weird ways and seem to instantly get confused. Let's try to build it ourselves to get that confusion out of the system.
So let's look at what we actually have to connect:
A car driving on A can either stay on A (for which we don't need any new connection) or change to C. Same for a car driving on B.
A car driving on D can either enter A or B.
So we need connections:
- From A to C
- From B to C
- From D to A
- From D to B
We can get 1. and 3. out of the way easily
For 2. we will have to cross the highway, so this is going to be a little more involved
And the last one is basically the same:
And there you have it. Your own fully working 3-way interchange. This will probably work pretty well. We can optimize a bit though:
In this one the entrance on B comes before the exit, so cars that exit might block ones that enter. Let's try to do it again the other way round:
That's it. If you compare it with the prefab, you will see that it's pretty much the same thing (just way more ugly).
The important thing to keep in mind when building an interchange like this are the 4 connections you have to make and the rest should follow