How do I upgrade roads on simcity 5 without destroying the existing road and all the buildings on it?

Under roads, next to the advisor's face there is a bunch of small icons. There is one that is an arrow that swoops up, its called upgrade roads, you pay the difference.

http://www.youtube.com/watch?v=kDipbRB9Bcw

Maybe you are wondering how to upgrade a Street into an Avenue without having to bulldoze everything in the area?  

The answer is you can't.  This is one I have been struggling with, because the optimal zoning between a Street and Avenue is different.  I am guessing that once you hit the stage where you need the Avenues, you have to raze a section at a time?

I saw a tutorial where he started with Avenues, and I tried for myself.  Of course I had to take out all 3 bonds, but it worked out, however I worked out.  

this is unacceptable.

Thank you!