I mean use a ramp to go up one level.
(http://i31.tinypic.com/347xrfp.jpg)
The way I know how to do it:
1. On the upper level, make some road so that you have a road end tile available
2. Use the terrain modification tools on the *end* road tile and push the tile down - that will create a ramp to the lower level that you can connect to when you go down to it.
It seems a little complex to me -- but this is a new feature, so there may well be some tweaking that will happen as time goes on... :)
I know (2) but what do you mean by (1)?
If you think of a road segment as a series of connected road tiles - push the one on the end down...