This view of some of Houston's freeway interchanges show just how dominant road infrastructure can be

A conversation with authors of a new book on the hidden geometry of urban transportation

I was recently sent an advance copy of a book, Transportation and the Shape of Cities, out on 4th August from Princeton University Press. And it’s not an exaggeration to say that it has changed how I view the challenge of moving city dwellers around. The book argues that space – rather than policy or politics – is the most significant limitation for transport in urban landscapes.

It focuses on the five major modes of transportation in US cities – pedestrian, micromobility (including bikes), car, train, and transit – and shows that each mode has its own geometry; a physical footprint that it needs in order to operate safely. The book visualizes these geometries through hundreds of scale drawings and illustrations, backed up by thorough research and real-world examples of how transport networks fit into urban design.

Transportation infrastructure will always take up space. In this image from the book, the turning radii of different modes are shown. The faster a vehicle travels, the wider its turning circle needs to be

The authors – Christof Spieler, David Copeland-Loredo, and Mandi Chapa – have spent years working together on planning projects across the US. Spieler is an engineer and now Director of Transportation for Madison, Wisconsin, after a long stint in Houston; Copeland-Loredo is a Houston-based planner and illustrator; Chapa is a planner trained in architecture who teaches urban transportation at Rice University.

Transportation and the Shape of Cities is predominantly written for planners, engineers, architects, and other professionals in urban design and city management. But it is packed with information that would appeal to an average city dweller who’s curious about their surroundings… which is exactly how I view my readers. So, last week, I hopped on a call with the three authors, to discuss their work, the book, and the challenges of building cities that offer transport options.

Where did the focus on the geometry of various transport networks come from?

"We've worked together on a bunch of different planning projects in very different contexts,” Spieler said. “Over and over again, you end up in the situation where you have the wish-list of what everybody wants, and then you try drawing it out and realize it doesn't fit. That is such a common pattern that it led to the realization that space is the most precious thing we have in the city." Chapa pointed to her and Copeland-Loredo's shared background in architecture – "I think the fact that in our work we take up space, we build has a lot to do with our view" – while Spieler, an engineer, said his instinct was “to look for constraints."

That framing extends to what Spieler thinks we get wrong most often: "I think most people actually underestimate how much space transportation takes. And they also overestimate how much flexibility there is with that. There's always this feeling, if you could just be a little more clever, you can figure this out. But there are some things you just can't figure out, no matter how clever you are."

How did the book come together?

The book grew out of an urban transportation systems class Spieler and Chapa began teaching together in 2015 in Rice's civil engineering department. “When we started to develop the lectures, we established the same sort of outline as the book now follows – split into transport modes and the scale of their networks,” says Chapa. Copeland-Loredo, originally brought in to illustrate class handouts, ended up producing all of the book's visual material – "over 500 illustrations or photos," by his estimate. That visual-first approach was a deliberate choice; a way to bring complex topics to life, to show “everything as physical objects that take up space”, and to support the written text.

For Spieler, one of their priorities was to ensure that all of the transport modes were discussed equally, “to treat all of these modes with the same rigor,” including the pedestrian, all-too-often left out of the technical language reserved for cars. " Cars are always treated with rigor – the idea that this has a turning radius and a lane width is built into conversations," Spieler said. "But pedestrians are also mechanical objects that move in space. They have every bit as much a requirement for space or for slope as other modes.”

That rigor produced surprising findings, even for the authors. Spieler learned from Chapa how rigid parking garage geometry is, meaning garages end up dictating the shape of developments around them. Copeland-Loredo offered a comparison that stuck with me: "A parked car might get a 9x18 or a 9x20 space in a garage. Meanwhile, in our offices, we might get an 8x8 space, meaning you could fit two of us in the space one of our cars takes up." He also cited the turning radius of a 200-mile-per-hour train – roughly 13,000 feet – against a bike's, at around eight feet.

Even when cars are not moving, they need ample space: a typical office worker has less workspace allocated to them in their cubicle than their car has allocated to it in the parking garage

Are there cities where you can trace a transportation decision's effect on urban form over time?

“In the United States it’s worth thinking about the cities that built out their freeway networks and those that didn't,” said Spieler. “LA is fascinating because it gives you a sense of what a city shaped around freeways feels like. And then you contrast it to San Francisco in the same state where they did not build out that network. You see how the urban form ended up looking very different as a result.”

Copeland-Loredo raised the development of transit systems in Washington D.C. and Baltimore as an example of the importance of “sticking to the plan”. The former has a Metrorail system that first began construction in 1969. Despite many changes in administration over the next three decades, construction continued with only minor changes to alignment. By 2001, all of the planned lines were operating. In Baltimore, a 71-mile metro system was first proposed in 1976. A decades-long cycle of political opposition and support has meant that only a fraction of the network has been built to date.

On the left (top and bottom), you see Washington DC's Metrorail network is the result of a long-term plan implemented in its original form. By 2001, all of the planned lines were operating. On the right (top), you see Detroit's metro system when it was first proposed in 1976, and what has been built to date (bottom)

“Ultimately,” said Spieler, “it's about the completeness of networks”. In the US, he said "we've basically built-in this idea that the car network is always complete" – legally, developers aren't even allowed to build somewhere without connecting it with a driveway to a roadway. But transit doesn't get that same treatment, he said, "We don't say there must be a transit line to every neighborhood, and so you end up with a kind of scarcity. You wouldn’t see gentrification effects if every neighborhood in the city had a subway station. They happen if only a handful of the neighborhoods get one."

Is there a mode pairing you think is undervalued?

Spieler made the case for walking plus transit, "We underestimate just how much a good transit network makes a city more walkable... a lot of transit design and planning has underestimated how important it is for people to be able to walk to the stations."

The transit hub itself, he argued, also needs to span scales, “If you’re building rail, you have these big stations and platforms, but that same infrastructure also has to work at the smaller scale of the human being and be linked into the fabric of the street. How far is it from the station to the nearest actual destination you would want to walk to?”

Chapa agreed, adding that she uses walking as her own way of learning a new transit system when she travels, “It's a very good way to figure out the geography. You can walk a little bit, and when you're tired, you can wait for the bus."

Copeland-Loredo made the case for a different pairing – bikes and transit. "It's almost a superpower whenever you're putting your bike on a train and you get to go so much further than you normally would." He brought up Houston's lack of a bike-share system during this year's football World Cup, when thousands of visiting fans had no easy way to cycle around. “I think we would have seen a lot of different activities going on if they’d had the option of taking a bike share, and might have seen people staying in different neighborhoods.” Rather than staying a 15-minute walk away from a transit station, “maybe they’d have stayed a 15-minute bike ride from the station, which would mean they’d see more of the city.”

Bike lanes are another form of transportation infrastructure that can safely move lots of people in relatively little space. These Paris commuters are riding their bikes in a cycle lane along Boulevard de Sebastopol, on a chilly Spring day. (Photo by Kiran RIDLEY)

What does a pedestrian-first city look like? How can that best include bikes?

“Just look at any city that was built more than 250 years ago,” laughed Spieler. “They have a completely different scale, because pedestrians simply do not need that much space. The key to walking being a useful mode is that you need to have all of the things you want within a reasonable distance from you. Walking thrives on density in a way that no other mode does.

Chapa agreed, saying, “A place that makes pedestrians thrive offers a lot of different things, services, activity within easy reach. Pedestrian streets also need all of those things that a living room offers. Lighting and seating, shelter, and a place to throw your trash.”

When bikes and scooters are incorporated into a street, the space requirements shift, “There's one way of thinking that says a bike is a somewhat bigger and faster kind of pedestrian,” said Spieler. “Another way of thinking is that a bike is a somewhat slower and smaller kind of car. And there's a third way of thinking that basically says a bike is its own thing. Those lead to dramatically different ways to design a street and a city.”

“It also has safety implications”, said Copeland-Loredo. “On projects we’re working on right now, we’re asking questions around whether there’s enough room to allow bikes in an area where there's a lot of foot traffic, or if they share the road for part of the route, what would that look like?”

How do you talk about the trade-off between flexibility and efficiency, if you're advising a city on whether to invest in a rail network?

“One thing to remember is that when you build infrastructure, you are shaping the future,” said Spieler. “Building a good subway line should influence development – it should make those places served by the stations more attractive for people to live in. And in that sense, a rail line sort of preserves its own utility. We might build transportation in response to urban form, but then as soon as we build it, that transportation starts shaping the city.”

He continued, “People talk about rail not being flexible, but freeways are not flexible either. Once you’ve built one, you can't really move it. We don’t talk about that because we've all gotten used to the idea that if you build a freeway, development follows. IF you do a rail line well, the same thing will happen.”

In their book, the authors focus on five major modes of transport. This graphic is their attempt to summarize the capacity of each mode in a given space of equal size. LOS (top image) is the "level of service" - a measure of how freely pedestrian traffic will flow. LOS-E represents a very busy street, where pedestrians need to adjust their gait as they walk.

Where do buses sit in the hierarchy of transportation modes?

Spieler didn't have to look far for an answer: "I am literally sitting at my window looking out at a dedicated bus lane with a transit priority signal," he said, noting that a single bus can carry 80 people far more space-efficiently than the equivalent number of single-occupant cars. “If you can give it its own lane, that allows it to be reliable and faster.”

Chapa described herself driving on Houston’s roads, identifying places where the bus routes could be given their own space, “I often find myself thinking that we [in cars] could all fit in one lane, to give priority to the buses. And it can be done.”

Copeland-Loredo also focused on his home city in his response, "Houston has the highest ridership bus route in all of Texas... it has some efficiencies like higher curbs at the bus stations, but it doesn't have that dedicated space. That's where you see that buses don't get the respect they deserve."

Taking space ‘away from cars’ is a hard political sell in most US cities. How do you talk about transportation with that in mind?

For Spieler, the key is to focus on capacity, “We're trying to move people, and we have limited space to move people in. What are our strategies? I’ve found that to be an enormously useful approach, because you realize you're solving a practical problem. You're not actually making an ideological statement.”

For Copeland-Loredo, safety needs to be part of the conversation, “Ask what is the safest option? So, talk about safety and how a lot of the extra space that we give to cars sometimes make things less safe. For example, giving one more foot of width to a lane might encourage people to drive faster, and that leads to more severe crashes.”

Chapa agreed with both, and reemphasized the importance of safe pedestrian access. “We're all pedestrians at some part of our trip. The majority of the time, we reach our final destination as a pedestrian on foot, in a wheelchair, on crutches.

She continued, “I remind people, when you go and visit places overseas, you get so excited about being able to get around without a car, but then you come back home and forget all about it. What if we had the city that you just visited? We could do the same thing here.”

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