While cars are about 30% efficient, this is far from the Carnot limit. Even in Otto cycle engines, like in typical car engines a compression ratio of 10:1 is enough to produce a theoretical cycle efficiency of 60% (http://scienceworld.wolfram.com/physics/OttoCycle.html).
Furthermore, not every car uses the Otto cycle and things like gas turbines (Brayton cycle), Diesel engines (Diesel cycle) do exist. Even existing turbo-compound diesel engines like the 3rd generation Diesel-Ethanol Scania 9-litre engine achieve thermal efficiencies of 43-44%, depending on fuel. There are also all sorts of potential future innovations, such as camless engines which have the potential to make engines smaller and lighter as well as increasing valve control so that more efficient cycles can be implemented. Then there's the possibility of adding additional power strokes, for example, by adding additional cylinders in which exhaust gases are further expanded, or by using water injection followed by two additional strokes to make use of the expanding steam.
Beyond this there are really experimental things like wave rotor engines and other inventions that may well continue to improve car engines to keep them competitive for well into the future, especially for people who like light vehicles with high power-to-weight ratio. Of course, batteries will still make sense, since hybrid configurations may permit engines to run at fixed loads and batteries might become lighter I still.
I especially doubt whether fully electric trucks and busses, a thus whether electric *vehicles* to achieve the goods and people moving capacities of gasoline powered vehicles, are practical at all, although I have little doubt that they will likely become hybrids.