Rustalots advice is great. Subways are awesome in reducing traffic, so are bus stops in a way. Be careful when building your Subway, or bus system. I didn't really know how a subway system worked until I went to Montreal this July. I actually got on a subway for the first time and checked out the map, and trust me there are LOTS of stops. I'm not saying you have to makes alot of subway stations, just start out in the mainly high traffic areas. My first successful subway involved one line of subway pipe and four subway stop. I placed one right by the main residential zone, one by the smaller Comercial area, one by the larger comercial area, and the last one by the large industrial area. It worked like a charm