Start by creating regulations on each vehicles emissions. The city should have a monthly limit to emissions and there should be sensors everywhere. the vehicles and factories around the city should almost entirely be electric, wind, or hydraulic powered. If the city is by any form of water, you should use water power and wind power. electric power from solar as well. some buildings could have solar on top and others could have small farms or gardens.

Transportation is obviously usually the factor that enlarges the total carbon footprint the most. I found that what most effected my amount of carbon produced from transportation was airplane flights, In particular two flights overseas. I'm wondering if we would be able to find another, more eco friendly way to transport people overseas- creating a sailboat/steamboat hybrid may be an interesting idea.
   As for transportation within cities, along with regulating emissions from vehicles it may be smart to find an alternative transportation altogether. Many people refrain from riding bikes in urban settings because of traffic dangers, but creating bike-only roads and regulations may not only encourage people to transport themselves via bike, but also discourage people from purchasing cars when the easiest routes to and from certain places are bike-only.

that is very true. although biking is sometimes difficult. do you suggest we make leaning to bike a simple application to learning to drive? or maybe a form of quadricycle? A bicycle with four wheels could be helpful in maintaining "green" uses and avoid having to teach people how to bike.