Charts count unique models per year, not sales. Powertrain mix uses the same tags as By year: gasoline, hybrid (including plug-in), battery-electric, diesel. Efficiency lines are medians. Class bars are the latest model year.
Q&A asks the catalog questions directly: whether median energy use fell, whether rated tailpipe CO₂ fell, whether hybrid and EV nameplates grew, whether SUV classes are a larger share, and whether gasoline-only unique models used less fuel. Compare a recent year (usually 2015) with the latest year in the guide.
Official files: Fuel consumption ratings on Open Government.