Why isn't my connections to the highway valid in Cities: Skylines?

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?

Solution 1:

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.

Solution 2:

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!