Game vehicles- What constitutes trademark infringement?

What I need to know is in the design of vehicles for video games, what constitutes trademark/copyright infringement? At what point does one need to get a license from the automotive manufacture? How much does a license even cost?

I have seen license statements for video games that include name, emblem, and body design. However, I have also seen video games that have vehicles with for example a 1968 Dodge Charger. It look like a Charger, but it is call something like a Nelson Eliminator and has no emblems on it. Doesn't that still violate the body design trademark?

Is there someplace I can look at what the rules/laws are governing this? It is causing some concern for my tema members and myself.