MPG/City and MPG/Highway are meaningful, and entirely sufficient, when applied to passenger-car use ~ which seems to be what the OP had in mind.

The additional caveats about the relative fuel-efficiency of different options for shipping freight are interesting additional information.

"City driving," insofar as it affects miles-per-gallon in the operation of an automobile, includes a goodly amount of idling (sitting at red lights, etc.), as well as inefficient changing of speeds, etc. That's why it always registers as less efficient than uninterrupted cruising-speed "highway driving."