One of the most important aspects of urban planning, both in real life and in SimCity, is transportation.
The importance of Transport in Real-life Urban Planning
In urban planning, there is a direct, well-researched connection between the density of an urban environment, and the amount of transport into that environment. Good quality transport is often followed by development. Development beyond a certain density can quickly overcrowd transport.
Good planning attempts to place higher densities of jobs or residents near high-volume transport. For example, some cities permit commerce and multi-storey apartment buildings only within one block of train stations and four-lane boulevards, and accept single-family dwellings and parks further away.
Densities are usually measured as the floor area of buildings divided by the land area, or in a residential context, by the number of dwellings divided by the land area. Floor area ratios below 1.5 are low density. Plot ratios above five are very high density. Most exurbs are below two, while most city centers are well above five. Walk-up apartments with basement garages can easily achieve a density of three. Skyscrapers easily achieve densities of thirty or more. Higher densities tempt developers with higher profits. City authorities may try to encourage lower densities to reduce infrastructure costs, though some observers note that low densities may not accommodate enough population to provide adequate demand or funding for that infrastructure.
Automobiles are well suited to serve densities as high as 1.5 with basic limited-access highways. Innovations such as car-pool lanes and rush hour-use taxes may get automobiles to neighbourhoods with plot ratios as high as 2.5.
Densities above 5 are well-served by trains. Most such areas were actually developed in response to trains in the middle 1800s, and have historically high ridership that have never used automobiles for their work trip.
A widespread problem is that there is a range of residential densities between about two and five that causes severe traffic jams of automobiles, yet are too low to be commercially served by trains or light rail. The conventional solution is to use buses, but these and light rail systems may fail where automobiles and excess road network capacity are both available, achieving less than 1% ridership. Some theoreticians speculate that personal rapid transit might coax people from their automobiles, and yet effectively serve intermediate densities, but this has not been demonstrated. The Lewis-Mogridge Position claims that increasing road space is not an effective way of relieving traffic jams as latent or induced demand invariably emerges to restore a socially-tolerable level of congestion.
Transport in SimCity
These concepts of urban planning in real cities have been carried into the SimCity games. Roads, trains, subways, highways, bus systems, are all major forms of transportation, and are how your Sims will be able to get around your city. Like a real life mayor, or an urban planner, SimCity requires you to make a choice about which modes of transport are appropriate for your city. Similarly, there are consequences for your choices (for example, choosing roads in a high-density city, as with real life, will lead to traffic congestion and pollution).
Traffic is generated from each residential, commercial or industrial zone to large residential buildings, as well as commercial centers, Naval Ports and Nuclear plants.
A road should provide a network between the zones and various other buildings within the city. For a zone to be connected to the traffic grid, it must have at least one adjacent road tile.
Maintenance costs $1 for each road tile, and $2 for each rail tile. You can safely bring the budget to 94% without ill effects, but further cuts will cause deterioration.