In the world of cars, both automakers and private inventors have come up with new technologies that seemed like great ideas, but never caught on with the bean counters and product planners. What was the most useful automotive innovation that never happened?

Has to be the "disappearing car door." Sure it adds acres of complexity to already creepingly complex automobiles, and it probably wouldn't have made it past side-impact safety standards. But there's something appealing about saying buh-buy to a car door when you open it up. No crawling around tight spots, no bumping other cars, no fingers caught in the door. We give this one a big, un-smashed thumb's up. (Thanks to lcyubnvs for today's QOTD).

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