I have just bought my first neighboring area and want to hook into it.
I first tried with a large roundabout and then with a three-way intersection, but none of them works. I keep getting the "broken" icon and the cars just disappears once they enter the area.
What have I done wrong?
It's hard to verify it because it isn't zoomed in but I'm 99% sure it's because your road is facing in one direction at one point and in the other direction in another.
Look at the arrows on the road, you'll notice that they're pointing towards eachother and essentially creating an impossible driving route.
To reverse the direction of a one-way road, use the road upgrade tool and Right Click the section of road that you want to reverse. This will work even if it gives you the "cannot upgrade roads of this type" error when you hover over it. Be sure to select the right kind of one-way road first!
To add on to Jeroen's answer, remember that one-way roads always go from where you click to start them to where you click to end them, independent of any other roads. Looking at the second picture specifically, my guess is that you built both of them by starting either from the end in the intersection or on the edge of the map, which means both sides of the road are going the same way, creating the issue that one side is considered incomplete.
