While it's not the raise or lower land tool, the next SimCity
update will bring forth a very welcomed feature. Version 7 will see the addition to raise and lower roads into the fray.
Raising the road high enough, you can create a new bridge that will allow roads to travel underneath it. If you go really low, you can eventually create a tunnel that could be pretty useful to direct traffic from one end of an area to another while going through some densely populated areas.
Overall, this looks like a nice feature to be added to SimCity as Maxis continues to improve on the game.