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A vintage 1968 car will emit more tailpipe emissions in the first two minutes of operation than a Prius will in an hour, especially if the Prius is in traffic and thus using its electric motor most of the time. They had nada for emissions control back then, not even recirculation of exhaust gasses, and a cold engine emits way, way more pollutants than a warm one.
If you want to be smug, I'm afraid you're going to have to walk or bicycle those three miles. Probably help your blood pressure, too. ;)