Think small. That’s what more of today’s car buyers are doing. But it’s not just new Volkswagens they’re buying. After several years of high gas prices and a sluggish economy, it seems U.S. consumers have finally taken to the idea of buying small, eco-friendly, fuel-efficient vehicles across the board. About half of all new cars sold in the U.S. now have smaller four-cylinder engines. Meanwhile, federal fuel-efficiency standards — which will double the m.p.g. standards for cars and light trucks by 2025 — will continue putting pressure on manufacturers to produce vehicles with smaller engines and better fuel economy. Consumers seem to be on board at a time when the industry as a whole has recovered after the government bailouts. Sales were up 13% in September from a year ago and are currently at their highest point since February 2008.