Here is a recent research paper by Christopher Barrington-Leigh and Adam Millard-Ball that looks at the connectivity of local street networks across the world. They refer to this as "street-network sprawl" and they measure it using a Street-Network Disconnectedness index (SNDi).
This is important for many reasons. Compact street networks with shorter blocks and fewer dead ends are far more conducive to different forms of mobility, including transit. Street networks are also incredibly sticky. Once laid, they rarely change. And if they do, it's over very long periods of time.
The study period in the paper is 1975 to 2013. What they found is that in 90% of the 134 most populous countries in the world, the street network has become less connected since 1975. What this means is that we have been making it harder to service our communities with transit.
That said, there has been a reversal in "high income" countries, most notably in North America. If you take a look at the above graphs, you can see a fairly dramatic drop off, signalling a reduction in the construction of low-connectivity streets. Southeast Asia, on the other hand, is trending in the opposite direction. Note Bangkok in the upper righthand corner.
For a copy of the full research paper, click here.
Images: Global trends toward urban street-network sprawl
