The simplest way to enforce this is to make what is called a "Mapcat Bowtie" (named after the #1-ranked editor, who came up with it). I've adjusted that intersection into the bowtie configuration so that you take a look at it and see how it's done, for future reference. Although it does look a bit strange in WME, it looks okay in the client, and it works perfectly for restricting U-turns in this type of intersection.