THE day I went to pick up my new Volkswagen Jetta TDI in March 2009, the salesman had me sit in the driver’s seat while he introduced the car’s various features. The engine was softly idling, and as I reached to shut it off, he told me not to bother. The minimal amount of fuel this car burned — sipped, in the automotive argot — was its great selling point. That, and the almost complete removal of hazardous exhaust that had made earlier diesel vehicles notorious.

This was that new thing in the world, “clean diesel,” using ingenious German technology to keep nitrogen oxide (NOx) emissions out of kids’ lungs, and low enough to meet even California’s stringent pollution standards. A committee of jurors, including the executive director of the Sierra Club and the president of the Natural Resources Defense Council, had just called it the “Green Car of the Year.” A review in this newspaper described the Jetta TDI, persuasively, as “easy on money, fuel and the planet.”

It was quiet, too. The salesman told me to rev the engine, to hear just how quiet, and I hesitated. I am not an engine revver by nature. I’d been writing articles and giving talks about the importance of cutting emissions and reducing our individual carbon footprints, or what I thought of, a little fatuously, as “the Kyoto Protocol at home.” I wondered if the salesman took some small pleasure from inflicting engine-revving torture on tiresome environmentally minded customers. Or maybe he was annoyed that I had not gone for any of the usual dealer add-ons. So throw the man a bone: I revved.

Then I drove off the lot and fell almost instantly in love. The Jetta TDI was fun to drive, unlike the plodding family Volvo it replaced. I fell particularly for what I thought of as “the number.” VW designers had cleverly placed the miles per gallon indicator front and center in the dashboard where other cars put the speedometer. On the highway, I could see that number changing moment by moment as I depressed the accelerator or shifted gears, and I adjusted my driving accordingly. The number averaged somewhere in the mid-40s on the drive home, at one point hitting 187 miles per gallon. It was like owning a Prius in disguise, without the spongy brakes or the self-righteous appearance of scolding the gas-guzzlers of the world. Coming into the driveway, I was doing my best “wah-wah” in roughly the manner of Ronny and the Daytonas singing “G.T.O.”