Tag Archives: speed

Speed, urban transportation and geometry heuristics

Following up on this previous post, noting that “transport is mostly a real estate problem” – a few quick heuristics on cities, speed, and space:

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Regarding speed: 

Speed requires space; faster travel occupies a larger area than slower travel.

Speed alters our perception of space. Faster travel makes large things seem smaller (hat tip to this post from GGW for the links). The properties of the space affect how we use it and what we percieve it to be; wider roadways within streets get used for faster travel.

Regardless of speed, cars require large spaces relative to their capacity. Even when parked (v = 0), cars require lots of space. By extension, building cities around requires a completely different spatial footprint.

Regarding space: 

There is a strong tendency for cities to devote about 25% of their land to streets. Street networks are for mobility, but also for access to land. Devoting too much land to streets is wasteful; too little makes it difficult to unlock the value of the land within a city.

Intersection density correlates with walkability and connectivity; wider instersection spacing correlates with the higher speed travel of cars.

Consider the relationship between the density of the network (intersection density), the tendency to use ~25% of land for streets (regardless of the density of the place), and street width on the kind of transportation.

Simply requiring some minimum intersection density for new developments via a code will still be subject to ‘gaming’ and open to unintended consequences.

Street networks are sticky and tend not to change once established; the cities that grow around them are path-dependent. However, transport networks can be layered – subways travel fast, require space and grade-separation, but deliver passengers to the street grid as pedestrians; just as freeways are layered above/below streets and deliver high volumes of cars to local streets.

While the physical space allocated to streets tends not to change, the use of that space can change a great deal over time.

The Need for Speed

A streetcar speeds by in Toronto. CC image from Matthew Burpee.

A streetcar speeds by in Toronto. CC image from Matthew Burpee.

Jarrett Walker has a wrap-up post on his debate with Patrick Condon on the need for speed in urban transit.   Condon is a professor of sustainability, not a transportation planner or engineer, and his view is that we need to improve the experience of sustainable transit and not enable the sprawling lifestyles of yesterday, no matter what mode we use to get to and fro.  Jarrett sums up Condon’s thesis in an earlier post:

Condon heads the Design Centre for Sustainability inside UBC’s Department of Architecture and Landscape Architecture, and is the author of the very useful book Design Charrettes for Sustainable Communities. In his 2008 paper “The Case for the Tram: Learning from Portland,” he explicitly states a radical idea that many urban planners are thinking about, but that not many of them say in public.  He suggests that the whole idea of moving large volumes of people relatively quickly across an urban region, as “rapid transit” systems do, is problematic or obsolete:

The question of operational speed conjures up a larger issue: who exactly are the intended beneficiaries of enhanced mobility? A high speed system is best if the main intention is to move riders quickly from one side of the region to the other.  Lower operational speeds are better if your intention is to best serve city districts with easy access within them and to support a long term objective to create more complete communities, less dependent on twice-daily cross-region trips.

It’s an interesting question, and it’s having a significant if not always visible impact on transport planning.  Darrin Nordahl’s 2009 book My Kind of Transit, reviewed here, also praises slow transit; he makes that case in the same way you’d advocate for “slow food,” by pointing to the richness of experience that comes only from slowing down.

The implication is clear, as Jarrett states in the title of his posts – “is speed obsolete?”  Jarrett’s counter-point, however, is that speed matters, and it matters a great deal:

So here’s my main point:

Rapid transit is a far more viable “augmenter” of pedestrian trips because its travel speeds, and thus the trip-lengths for which it’s suited, lie entirely outside the pedestrian’s range, whereas the streetcar overlaps the pedestrian range substantially.

The rapid transit and pedestrian modes play entirely complementary roles, while streetcar and pedestrian modes have partly overlapping roles — a less efficient arrangement.  You’ll walk further to a rapid transit station, but once you’re there you can move at a high speed that makes that extra walk worthwhile […]

Rapid transit’s speed also exceeds typical cycling speed, by a large enough factor that it makes sense to cycle to the station.  So rapid transit works with cycling to a degree that local stop transit, such as the Portland Streetcar, just doesn’t.

Obviously, the usefulness of rapid transit requires a longer trip length, so rapid transit should be considered only for relatively long corridors.  As several commenters have mentioned, the problem with Condon’s view may be in the corridors to which he’s applied it, including Vancouver’s Broadway corridor, where he’s presented it as an alternative to a SkyTrain extension.

Streetcars and rapid transit are different tools, each suited for different jobs.  I’d argue that some of the value in streetcars is precisely because they can fill in the gaps of a hub-and-spoke system like Metro, while the aforementioned Broadway corridor in Vancouver probably should be one of the spokes. The question is then one of how you use that tool.  One thing to remember about Portland’s streetcar is that the station spacing is very close, especially when you consider Portland’s short blocks. Small adjustments, such as wider station spacing and some signal priority treatments could greatly improve performance and reliability.

DC’s proposed streetcar system can take better advantages of the streetcar’s strengths as a mode.  Yonah Freemark’s excellent graphics on DC’s network show how streetcars can fill in some of the crosstown gaps that exist in the current Metro network. However, streetcars certainly are not and cannot be a substitute for Metro’s utility to the city and the region.  Yonah also chimes in on the subject over at The Next American City:

By advocating streetcars, Condon is implicitly arguing that people should stay in their neighborhoods for most of their trips; that they should find work, go shopping, and be entertained in their near surroundings. If people have to rely on slow transit, they simply won’t have the time to be making trips across the region. (Or, of course, they might switch to driving their private automobiles, which would defeat the point of the transit investment entirely.)Though this approach would likely produce better ecological outcomes (less energy consumption per person as a result of reduced transport mileage), it would exacerbate spatial inequalities. Because jobs (especially well-paid ones) tend to be concentrated in the favored quarter, poorer inhabitants living far away from that zone would be isolated from employment opportunities and thus be deprived of chances for income growth. Or they would face devastatingly long commutes.

Stepping outside of the fiscally constrained world, the obvious answer is that both rapid and circulator systems serve different and complimentary needs.  The economic implications (for a city’s economy, rather than just real estate development) are the really interesting – Walker’s commenter ‘micasa’ highlights Jane Jacobs and the very nature of cities:

What does the venerable Jane Jacobs have to say about the notion of a “city of neighbourhoods”?

“Whatever city neighborhoods may be, or may not be, and whatever usefulness they may have, or may be coaxed into having, their qualities cannot work at cross-purposes to thoroughgoing city mobility and fluidity of use, without economically weakening the city of which they are a part. The lack of either economic or social self-containment is natural and necessary to city neighborhoods – simply because they are parts of cities.”

Jacobs is describing what does, and always has, made cities “tick”.  To be against intra-urban mobility is to be against the very proposition of the city.  I don’t think we can afford to let the threat of climate change, peak oil, or whatever, destroy that. We may need radically different, more sustainable cities in the future if we are going to survive, but rest assured, we will still need cities. Not agglomerations of inward focused neighbourhoods, but cities.

I’m not suggesting that the debate over transit technologies in this particular case ought to be closed. But I am suggesting that Condon’s particular argument for surface rail – that it encourages local living in a neighbourhood setting – is fundamentally anti-urban.  A better argument, and one that actually addresses the urban mobility issue, is that perhaps surface rail is a cheaper solution that can be designed “fast enough” to allow those neighbourhoods on the West Side (including UBC) to cohere with the rest of the region without the necessity of cars (and vice-versa). But that’s not the argument as presented.

Is speed obsolete?  I’d say no.  To micasa’s last point, surface rail can indeed be designed to be ‘fast enough’ to address urban mobility, particularly when paired with an existing rapid transit system (such as DC’s Metro).