I've seen some of the videos of Copenhagen at rush-hour, and if those were cars, it would be an endless parking lot (funny, but sad).
While it's true that energy efficiency is less important with clean power, It can make a huge dent in emissions in the meantime. A perfect example of that is the transition into LED lightbulbs. Currently, not only do they reduce emissions, they make off grid solar installs much more effective and cheaper. Even for folks like us that have grid-tied solar power, better energy efficiency allows more of that solar power to flow to the grid and offset dirty power.
Even with totally clean power, the much higher efficiency of an electric bicycle compared to a car would allow a single 100 W solar panel to power my transportation needs, compared to eight 275 W solar panels. While the environmental impact of manufacturing solar panels is fairly minimal, the more efficient our energy usage is, less generation equipment is required, further saving energy and resources.