An internal combustion engine, alone, mounted on a test bench,
will convert about 10-20 percent of the potential energy in gasoline
into rotary motion [turning the crank/drive shaft unconnected to any vehicle].

But transmission friction. air resistance, road and tire imperfections, travel oscillations, braking, slowing, accelerating, etc., quickly reduce efficiency dramatically
between points A and Points B travelled by an automobile; wasting most
of the remaining potential-energy of gasoline overcoming these factors.

I'm going to look at the PBS website to locate the info on last night's program.