Downsize ? ... Now consider large population numbers being able to work from home instead. Yes they will be using energy at home, but we eliminate the commute, we eliminate the additional buildings to build, maintain and which also use energy. ...
But they will need to get food from more central supplies, see doctors far from their suburban homes, go to pubs, dance halls etc. to socialize so still need their cars. Man is by nature a social creature - not a hermit in his home.
We need to re-think the city (no private cars) etc. I have done so in old post I will try to find of a very green city with tilted pyramidal buildings (vertical North wall in Northern Hemisphere and each level smaller so has perimeter "U shaped" green space on all levels - from high above the city looks like pasture or forest.
Most of my old post deals with the "autocar" shared transportation system, which resembles a "horizontal elevator" - I.e. you push a few buttons telling the system where you want to go, how many of you are traveling together and it prints your bar code key to the autocar that takes you there via a controlled access pathway, very fast in a locked autocar than never stops until you arrive at the autocar terminal in each building ground floor center as there are no intersection, stop lights, or traffic jams, etc. I.e. it is very much like an elevator - controlled access pathway, a locked car with limited exit spots, etc.
If you need or want to exit sooner, you can hit your only control, the "stop button," (like hitting the next floor button coming up in an elevator) and autocars stops at the closest auto car terminal for you to get out. The entire system is under computer control, again like an elevator, just more complex.
Did you know that elevators are the safest form of transportation by far on a passenger mile basis - the autocar system will be even safer as the computer has alternate route to go from A to B and controls all movement within the system. When you leave the autocar it goes to the local cleaning center. (If you messed it up, your monthly bill will be higher or your pre paid deposit may be eaten up.) Autocars come in 2, 4 or 6 passenger sizes.
This brief description given as I may not be able to find the full description of the city (or you may not want to read about the internal layout / uses of the pyramidal buildings, covered bike pathways, time of use billing system of autocars to avoid demand over loads etc.)
Just one comment on the internal use of the buildings -People live on the higher levels (and can smoke only in the top roof park) and most commute to work places in the lower levels by elevator or if they work in a different building, the bike pathway level or the autocar terminal on the ground level
Later, by edit: It was easy to find links to old my old post via machine search of all my posts with "autocar" as the entry item:
For more on the autocar system see:
http://www.sciforums.com/showpost.php?p=2228529&postcount=74
For more about the city plan see:
http://www.sciforums.com/showpost.php?p=2228211&postcount=71
but there is an earlier more detailed post in some thread about modern cities I did not find.