27/09 - True, there have been efficiency gains in automobiles, with "gearbox and drive train improvements, weight reductions, more aerodynamic shapes, etc."
However, there have been pure fuel efficiency gains in auto engines, to the order of around up to 50% in the last 40 years alone.
Not surprisingly, the affluence of Western nations has seen these gains negated, as auto buyers have elected to buy heavier vehicles such as 4WD's, pickups and SUV's in vastly increased numbers in the last 25 years.
In addition, those more affluent Westerners have also demanded a lot more luxury accessories such as high quality onboard entertainment and communication systems, luxurious interiors, more safety features such as multiple airbags, "luxury" accessories such as climate control, electric windows all round, heavier multi-speed transmissions (GM's latest offering is a 10 speed automatic), and a host of other add-ons that all increase weight and impact on fuel efficiency.
In addition, many of the latest emission control devices on low-emission engines, have incurred fuel efficiency penalties as the emission devices such as EGR work against fuel efficiency.
Car and driver.com (2006) - Why gas mileage hasn't improved in 25 years
We still look to the racing field to provide substantial efficiency improvements, as a means for power output increases. However, many racing developments have spin-off potential for improved fuel efficiency in ordinary autos.
Arstechnica.com - 2016/05 - Turbulent times for Formula 1 engines results in unprecedented (engine) efficiency gains (excuse the excruciatingly simplistic technology descriptions)