Cities don’t look like they used to. Working class neighbourhoods are turning into yuppie enclaves. Industrial zones are turning into hipster fiefdoms. Whether it’s Williamsburg, Brooklyn or Neukölln, Berlin, residents are picking new neighbourhoods for their homes and businesses — and they’re often a good clip away from “traditional” city centres. As new areas densify and city poles shift, how do cities themselves adapt?

If you look at any city’s transit network, there’s a good chance that it will follow decades-old migration patterns, with subways stuck in their place, and buses following the same routes that horse-drawn omnibuses and streetcars did. Obviously this poses problems when a neighbourhood equipped for light transit volumes is suddenly overburdened with hordes of new people.

Since the Williamsburg boom started in the late 1990s, the L-Train has struggled to keep up. Photo: New York Times.

This isn’t just a problem for megacities like New York City. Even smaller cities like Honolulu are being strangled by gridlock as new residents (and their cars) take to the streets. Public transit would be a better mobility solution — no other mode can move so many people in so few vehicles. However, it’s hard to convince people to take public transit when its routes are slow, infrequent, and don’t get people where they want to go.

Increasingly, cities are realizing that effective public transit is the best way to accommodate their growing and densifying population. But how do transit networks adapt? How do cities determine which areas are underserved by transit? How do they design new optimal routes? Do they add buses, streetcars, or bore holes for a subway? Do they run all-day service or expresses?

For the last twenty years, there’s been one person that cities have sought out for advice on these questions. His name is Jarrett Walker.

Jarrett Walker, Transit Whisperer.

Jarrett Walker is a transit planner from Portland, Oregon. It is not an understatement to say that — at least in transit circles — Walker is God. His book is the transit nerd’s bible, his blog is their pew and kneeler. He is often on tour, stumping for the importance of public transportation in today’s cities. He sometimes plays the role of Twitter contrarian, lampooning Silicon Valley’s tech hawks for thinking gridlock can be solved by replacing single-occupant cars with single-occupant driverless cars. He has built his reputation over a decades-long career, and helped redesign (either directly, or by way of his consulting firm, Jarrett Walker & Associates) transit systems in dozens of cities, across North America, Australia, and New Zealand.

Walker looks at the demography of a city and its existing transit network — where are jobs, housing, existing ridership? Then, with a combination of local knowledge, data crunching, and network design principles, he and his team weave together transit plans that help cities meet their goals, which are often myriad.

There are tons of tough calls involved in designing new transit systems: do you shoot for maximum ridership — at the expense of reduced service in other areas? Or do you try and serve each neighbourhood — even if that means service in denser neighbourhoods will suffer? How do you handle NIMBYism, tight budgets, and soaring infrastructure costs? How do you explain to someone that the bus they’ve relied on for 10 years is being cut (because it serves 10 people an hour and it can be reallocated to an area where it can serve 100?)

Navigating these tradeoffs is a tricky ballet, and transit planners like Walker work with agencies and community groups for months or even years planning new networks. Credit also goes to city leaders who display immense amounts of courage, exert political capital, and spend time convincing their neighbourhoods that rejigging (or replacing) routes is necessary.

However, when it comes to actually rolling these changes out, it often doesn’t take Walker & co. much time at all.