The City Hall requires 600,000 population to add all modules to win the Big Government Achievement, plus the Jumbo and Mega region Achievements require packing in a lot of Sims in each city unless you use one of the really big regions. The game does encourage population growth (the first Sim World challenge was a population boom challenge).
I am going to suggest something perhaps slightly radical and possibly unacceptible here, which is that the best way to deal with large populations in SimCity is not to have them. The other two had a much longer life span before traffic problems began to make them unusable, although the curved road does take up more space! High Populations & Traffic Problems The 'grid' solution on the left is horrible and jams quickly. Here are a few of examples of road layouts around the highway connection which I have tried in some of my cities. If you're relying on commodities trading for income then getting the upgraded trade port to ship goods by sea and rail should be a priority. Ensure that roads where delivery vehicles interact with other city traffic is kept to a minimum. Where possible keep specialization chains together, like storage depots, mines, factories etc. event centers, universities, tourist attractions, high density factories etc). Spread out buildings that generate heavy traffic (i.e. Not zoning areas along the main exit route will help reduce congestion. I would also recommend not bringing streetcar avenues right up to the highway connection because it also puts an additional junction close to the busy exit. Avoiding 4 way junctions is a good strategy in general, but particularly on the connection to the region.
Regardless of the arrangement of the highway exits in your city, you can reduce congestion by increasing the distance between the exit and the first junction. Getting the most out of your road network starts with dealing with the connection to the highway. Planning for Avenues in Early City Development.The following sections can be found in this article: This topic was originally designed to be much longer with examples of different basic road patterns etc, but to be honest I really couldn't find any that really worked with city-sized populations!