Sorry about that, I was delayed in getting new hardwar to help work on the site and help with adding content so I wasn't able to see this post till now.
But putting highways down is VERY hard, but there are some tricks to it. One thing is to place the highway end peices first (like on/off ramps and then conntect the highway and then the avenue to the highway.
One thing that will stop you from making this work is terrain! You must have completely even terrain, one tiny bump can ruin a large area of unused space, so you have to keep that in mind. Make sure its flat, open, and not block by water or the edge of the map.
I might actually do a video now that you mention it just to show how it is done. But for me, the MC team pretty much let me get to the end of the game, and I found the guy behind the curtain, so now I am just waiting for them to add something more for me to do in teh game, otherwise I would be taking advantage of the subscription money I already forked over ;/
But also I wanted to say excellent work on getting some activity onto the cities xl section

I will keep tabs on the forums a bit more while I am multi-tasking the various projects in the works.
So, Post and ye shall be answered.