Thinking Further on Marchetti’s Constant

We’ve been thinking a lot lately about Marchetti’s constant, the idea that people will spend an hour commuting each day, or half an hour each way and adjust lives accordingly based on transportation technologies and housing location choices.

Two research papers posted today feed into that with interesting results. Using data from the Canadian Mobility Survey, researchers at McGill University sought to determine some of the factors that would get people back on transit after the pandemic. What they found was that people that identified as transit riders and had recent transit use were likely future riders with non-users indicating low use intention.

But also included are those (52% of respondents) who believe a 20-35 minute door to door transit trip is reasonable. That time allowance would fit Marchetti’s constant of ~30 minutes commute one way which as Carvalho and El-Geneidy suggest should induce transportation planners to prioritize transit service and projects that get people to jobs within that time window.

The barrier however seems to be car use and people’s sunk in habits which can be psychologically hard to break. Even free transit as seen by researchers in Australia can not seem to break through that car barrier. In some instances though, we know when someone moves to a new house, there’s a possible window for change.

A second research paper in JAPA written in part by our friends Shima Hamidi and Reid Ewing also show another tide pushing against transit usage; the increase in sprawling development. But they found certain levels of compactness increase more active transportation uses while drive times and car ownership went against it. I would then personally posit that building more housing further out blows up any possibility that transit travel times could fit inside of Marchetti’s Constant.

Of course there are new wrinkles in the discussion. Work from home has become more popular for certain professionals post pandemic and commuting is only one type of trip. But Marchetti’s Constant cut in half for other trips ends up in a discussion about 15 minute cities and relates to our previous entries around time poverty and time based planning.

So then what are the solutions that give people a comfortable commute and an affordable home?  We could pave everything over and keep sprawling. That’s the option we continue to choose. Though I still think we’re running out of land for sprawl and from an economic and social standpoint we are hitting a dead end with our singular auto based paradigm.

Or we could be more strategic in thinking about what this actually means from an affordability and quality of life standpoint for residents of our cities. Perhaps Marchetti’s Constant shows us a way forward for cities in a larger context.

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