Sometimes it seems like the growth of a city is accompanied by even more growth in traffic congestion. At least that’s the impression I got living in Los Angeles during the years when most of its freeways were built. But was my subjective impression really true? The traffic patterns of real cities are so complicated that it can be difficult to discern the basic underlying principals. There are countless factors, not all of which are knowable, that influence the behavior of a transit system. So we have chosen to analyze a simple idealized traffic network to see how it works. If you’re curious, you can find the technical note How Transportation Network Size Effects Congestion on our Publications page.