Ok, I'm having a little problem...

I have a Car being followed by 2 weird UFO craft. I have a camera positioned and looking at a helper.  Everything is currently linked to the car as I want the camera in front of the car focused a the passenger side and the flying UFO's are flying behind the car in pursuit.

Now I want to drag the ensemble to the "spline road" so I turn on Collision Detection and attempt to drag the car ensemble down to the road.... FREEZE.... wait....

Carrara comes to its senses again... and I notice that the car has not moved... so I drag it down again....FREEZE.... same thing nothing happened.

Can someone help me clarify what it is I'm doing wrong. and how I will be able to drag the car down to touch the road without it going through?

EDIT: I guess in the end I could just punch in the numbers but I just want to know if this is typical or my procedure is the wrong way to do this.

Carrara 7 Pro, Anime Studio Pro 8, Hexagon 2.5, Zbrush 4.6, trueSpace 7.6, and Corel Draw X3. Manga Studio 4EX, Open Canvas 5, WACOM Cintiq 12WX User