So I finally hit 500,000 pop and now I can finally build that big, huge highway through my city that I always wanted right? Wrong! Well, the game's design tools really try their best to prevent you from doing what you want with a highway. First of all, the intersections are huge unmodifiable pieces that must be placed first before building the highway or connecting roads itself. It's very difficult to make things connect properly. For instance, you must use the large luxurious avenue to connect to a avenue/highway interchange,no other types will work. There doesn't seem to be any way to build an elevated highway. As soon as I started raising it, the tool would snap it back to the ground. Since the connection types are so limited it makes it neraly impossible to build a highway running through your city which is kind of the point of having a highway in the 1st place. Since you can't easily run roads under or over the highway, it will instead divide your city in half if you're not careful.
After some testing, trial and error I found a way to make it work for my city. As you'll see inthe screen shots below I downgraded the highway to an expressway intersection when I needed it to cross my existing expressway. For the next avenue connection I used a T-interchange which worked well for my situation. For the rest of the highway I plan to build a cloverleaf in the south area near the shore. These types of interesctions let you easily connect highways together and I want to have a highway running east towards my main industry, south towards what will be the future downtown commercial core (on the island) and west to provide quick transportation from a far distance to the commercial area from residential. There will also be north arm which I'm in the progress of building now. The goal is to use the highways to go through the middle of my city to facilitate fast traffic flow from most areas all the way to downtown.