It's hard, and will take decades. That said, there are a few things you can do relatively easily to make a start. 1. get rid of zoning laws that prevent buildi

It's hard, and will take decades. That said, there are a few things you can do relatively easily to make a start. 1. get rid of zoning laws that prevent building multi-family units. 2. invest heavily in public transit. Buses are great if they are widespread and arrive frequently. 3. in areas that have significant traffic, use trams/subways instead of buses. They carry way more people and don't sit in traffic. 4. make city centers dramatically more walkable. A 4 lane street is much harder to cross than a 2 lane street (or 2 one way 2 lane streets). 5. don't build new roads/highway exits that will encourage further sprawl.