This is my first post here. I've been playing TheoTown for a couple of weeks, and it's off to a great start. Even as an alpha release it's already better than any of the other city building games I've played on my phone.
This is a fairly ambitious proposal, and so would probably need to wait for a later release, but it would be great to have a transportation infrastructure to manage. I'm thinking of the following elements:
1. Transportation needs should be dictated by population density. Denser populations require more transit options. As population density increases, you also need to account for different kinds of travel. For example, some percentage of traffic is short distance, but some is long distance, and you don't want the long-distance travelers clogging up your city streets. Transit options other than basic roads should have ongoing costs, and some of them should have revenue. See my entry on subways.
2. More road types, rated for different amounts of traffic.
3. Highways. This would accommodate long distance travel, and would be built to connect dense population areas. I have this separate from the "more road types" option because highways are different. They need on/off ramps, have limits on how sharply they can curve, etc.
4. Subway system. Another way to reduce street congestion and pollution. Subways should be expensive to build and have a relatively high ongoing cost, but the ongoing cost can be offset with revenue. Revenue would be based on usage, extrapolated from population density and availability of other transit options.
5. Bus system. Establish a bus depot and overlay bus routes. Cheaper than subway, but handles less volume.
6. Light rail. Cheaper than subways, so better for long distance. Connections to suburbs, or between population centers.
All of the above were for transport from place to place within the city, but cities also have connections to the outside world. Here are some thoughts about that. None of this is about networking with other people's cities, just about connections with theoretical other cities.
1. Airport. There should be a regional airport which can be upgraded to an international airport. It should have an ongoing cost, but it should also improve your business sectors, so creating an airport will skew commercial buildings to larger and more valuable. The idea is that if your airport is the right size relative to your population it will be a net benefit because it will increase revenue from your commercial sectors.
2. Seaport. Same basic idea as the Airport, but for your industrial sectors.
3. Railroad. Combination of freight and passenger trains. Same basic idea as the Airport and Seaport, but cheaper and intended to be built earlier in the development of the city. For railroads to be active, they would need to go to the edge of the map
Some of this stuff could be built just as decoration at first, with the technical functionality to come later.