Modeling

quote of the week: on modeling

There is a popular illusion that confronting a computer with one’s ideas enforces rigor and discipline, thereby encouraging the researcher to reject or clarify fuzzy ideas.  In the very narrow sense that the human must behave exactly like a machine in order to communicate with it this is true.  But in a more useful sense, the effect is the opposite; it is all too easy to become immersed in the trivial details of working with a problem on the computer, rather than think through it rationally.  The effort of making the computer understand is then mistaken for intellectual activity and creative problem solving.

Douglass B. Lee, Jr., “Requiem for Large Scale Models
Journal of the American Institute of Planners
May 1973, Vol. 38, No. 3 (emphasis added)

“Abundant Access”: a map of a community’s transit choices, and a possible goal of transit

In my book Human Transit, I argued that the underlying geometry of transit requires communities to make a series of choices, each of which is a tradeoff between two things that are popular.  I argued that these hard choices are appropriate assignments for elected boards, because there is no technical ground for making one choice or the other.  What you choose should depend on what your community wants transit to do.  Examples of these choices include the following:  Continue Reading →

the need for maps of your freedom

 

Remember this map?

 

GoogEarth walkscore

I used it in the earliest days of this blog, and it's in almost every presentation I do.  It's from a tool that allows you to select a location in a city and see blobs (technically isochrones) showing the area you can get to in a fixed amount of time using transit plus walking.  This one is for 9:00 am and the three shades of blue represent travel times of 15, 30, or 45 minutes. In essence, the software takes the point you select and runs the equivalent of Google Transit trip planning searches to find a points where the travel time crosses the threshold; these become the boundaries of the blobs.  (For details behind this crude summary, see Aaron Antrim's comment on this post.)

I call this a map of your freedom.  It's useful for two potentially transformative purposes:

  • Helping people and organizations understand the transit consequences of where they choose to locate, and thus to take more responsbility for those consequences.  This, over time, can help people who value good transit to locate where transit access is good — something that's very hard to discern from a typical bus map but that becomes very obvious here.  You can even assess access to specific things that you value, based on exactly where the blobs are.  
  • Helping people visualise the benefit of transit — access to your city — as a freedom, and thus to understand more clearly what transit does for them.  It broadens the narrow notion of travel time  – which is often understood for only one typical trip — into a picture of your possibilities as a transit rider.  The percentage of a city's resources (jobs, housing, retail etc) that is in the blobs for a particular location could also form the basis for a meaningful Transit Score that could replace the technologically biased scores now used by WalkScore.com.

The original tool is a beta buried deep in WalkScore's archives.  It's basic and very, very slow.  

The other main alternative is mapnificent.net, by Stefan Wehrmeyer.  Available for many cities, Mapnificent.net looks good …

Mapnificent

… except that it contains two fatal assumptions:

  • Initial wait time is excluded.
  • Some timing of transfers is assumed, based on the author's experiences in Europe.  So he uses an average transfer wait time of 1/3 of the headway instead of 1/2 of the headway, which would be appropriate for random transfers.

Here's the problem.  Both assumptions mean that Mapnificent's assumptions undervalue frequency and overvalue vehicle speed. Since this conceptual bias is already very, very common (see Chapter 3 of my book), Mapnificent is seriously misleading in a way that can be really unhelpful.  For cities that I know, especially area with lower frequency service, Mapnificent wildly overstates the convenience of transit, and fails to show how locating on frequent service will get you better access to the city.

In my network design course we talk about this.  When figuring travel times in the course, I insist on using 1/2 of the headway as the intial wait time and the same as the transfer time (unless there's a pulse) so that frequencies weigh heavily into true travel times, as they do in life.  This sometimes sounds silly: If a route runs once an hour does that really mean I wait an average of 30 minutes?  Or do I just build my life around the schedule?  I view the two as the same thing, really.  We're not describing literal waiting so much as time when you're in the wrong place.  We're describing the difference between when you need to arrive and when you can actually arrive.  This could take the form of arriving at work 29 minutes earlier than your shift starts — consistently, every day.  Effectively, you end up waiting at your destination.

So there are a range of judgment calls to be made in designing these things, but it's worth getting it right because the potential utility of this tool is so significant.  The good news: I'm involved with people who are working on something better.  Stay tuned!

frequent service, mapped to your door

Vancouver's TransLink is one of several agencies who — with some input from me — have adopted Frequent Network brands that are designed to highlight services that are always coming soon, generally every 15 minutes or better all day and weekend.    I've always insisted that the Frequent Network can be both a short-term service branding tool (to build ridership by helping time-sensitive customers see where the network can serve them) but also a land use planning tool.

TransLink always understood it was both, and for several years has had a goal stating that half the region's population and jobs will be on the Frequent Network.  This is both a land use planning statement and a transit planning statement.  The message is not that TransLink will extend Frequent service to half the current population, but rather that it will do some of this while land use planning will also bring put residents and jobs on the existing Frequent Network.  More recently, Translink finally highlighted its Frequent Network on its maps for the public.

Ultimately, the Frequent Network, if properly mapped and promoted, should sell real estate, because the high level of all-day access should have a clear value as a city as a whole becomes more transit-oriented.  So this kind of micro-mapping should be really handy:

Ftn_skytrain_walksheds-1-2
This map (click to enlarge and sharpen) of transit access in New Westminster, British Columbia is by Jonathan X. Cote, a City Councilor in that city and also an urban planning student at Simon Fraser Univerisity. He takes the standard walking distances of 800m to rapid transit and 400m to local transit and plots the portion of his city that has access to those networks.  I've seen these maps before, and even if they are not drawn they are what lies behind any coherent statement about what percentage of population and jobs have transit access, within a given walking distance, to service of a given standard.

Remember:  If your city wants to do really honest transit analysis, it needs very small analysis zones.  This map shows you the kind of clarity that you get when you can analyze right down to the parcel.  You don't need that much fine grain, but the zones need to be small.  And a parcel-level map like this is certainly ideal for land use planners, who need to minimize walking distances for the centroids of transit-oriented developments. 

Notice what a good tool this is for analyzing bus stop spacing as well.  You can move the stops a little apart and count how many parcels fall out of the walkshed.  Out to about 400m (1/4mi) spacing the answer is usually "fewer than you expected."

using dynamite for lack of paint: alex broner on “cities in motion”

Ever since I posted on SimCity and SimCity 4 people have been telling me I must try Cities in Motion.  But when you have two jobs and you're already devoting hours to a blog and a book and a remodel, there is only so much time for computer games.  Fortunately, Alex Broner has boldly gone there in a guest post, so I don't have to!

 

CitiesinMotion_Image3In Cities in Motion (a game by Colossal Order, published by Paradox Interactive), one assumes the role of a CEO of a transit company tasked with providing transit to a particular city. In the campaign mode the cities are all based on specific cities at specific historical periods, Berlin during the cold war for example. There is also a “sandbox” mode in which you can play additional cities including player created cities and fictional cities.

Your transit company operates without subsidies for the most part, though there are “missions” which often offer monetary rewards for their completion. The most common mission is to connect two or more places together with a transit line.

In the campaign mode there are certain required missions which you must complete in order to “win” the scenario and unlock further scenarios.

Your transit company has a variety of different vehicle types which it can use to meet the needs of the city’s residents: Buses, trams, Metro, waterbuses, and helecopters.  There is (premium) downloadable content that adds electric trolleybuses, cable cars, and monorails.

CitiesinMotion_Image2Your success of failure in the game depends on finding ways to efficiently provide service connecting residents with destinations such as workplaces, shopping, leisure, and government. “Leisure” seems to include regional transportation hubs such as inter-city rail stations and airports. Like a real transit company, you must consider expenses for capital improvements such as stations and vehicles and also operational expenses such as labor and fuel/electricity.

This is not a city building game but the connection between density and transit service is made clear by the simple fact that even though you can build a subway to rural or suburban area, very few people will ride it.  The connection between service levels, frequency, and customer satisfaction is made clear by the “wait time” indicator. If the wait time on your transit lines is too long then customers will grow dissatisfied and eventually leave the station. Also, since all infrastructure such as stations and rails has maintenance cost, creating under-utilized infrastructure leads to a poor cost-revenue ratio.

17_0To be successful your agency must take into account the layout of the city and where different groups of people want to go: working class people work at working class jobs, students go to the university, professionals to the offices, and so on. Then you must make choices between vehicle types and network arrangements and put it all together into a profitable enterprise.

All of this is pretty realistic but as I played I immediately began noticing some major problems. The most notable problem is that the “walk shed” for each stop or station is different for each type of vehicle. The game will have residents walk much farther for metro service than they will for buses or trams, no matter how poor the metro service is or how good the buses and trams.

An additional problem is that there is nothing like transit lanes or transit signal priority for buses and trams. The streets of Cities in Motion have various amounts of traffic and in heavy traffic your vehicles will bunch up, depriving you of much needed revenue and making your riders unhappy. One's tools for dealing with this are limited: trams can run on unoccupied ground such as across plazas or on grass. Often in the game I find myself building a tram because there’s a long park or other way to bypass congestion. One can demolish buildings that get in the way of your trams but not build roads or even transit lanes, placing one in the bizarre situation of reaching for the dynamite for lack of paint. In combination the limited walk shed and lack of prioritization tools such as transit lanes means that the game very quickly becomes about building Metro systems. Not only is this unrealistic it’s also quite boring.

Additional annoying features:

  • Cyclical economic changes causes one to have to adjust ticket prices and labor pay rates constantly for each type of vehicle and 5 types of employees. There’s a mod that allows one to do this automatically but it would have been nice if that had been included in the base game.
  • Residents are drawn to transit in an almost fanatical fashion, they will navigate around any barrier to reach a station that’s close enough by straight line distance. One is not encouraged to situate stations in places realistically accessible. The routing algorithm of residents is poor meaning that they’ll pile up on the platform of one metro station even if there’s an empty platform with comparable services right nearby. 
  • Metro trains try to get 100% full before departing, even if this means holding up the empty train behind them. 
  • Finally, one is unable to combine either metro or tram vehicles to form longer trains (or construct longer platforms).

On the whole I give the game a B- for gameplay and a C for simulation value. It obsesses over certain aspects of transit (different types of customers, different types of workers, etc) while failing to address some really important ones. It teaches some important things about transit (frequency, density, operation costs) while furthering our confusion about the relationship between technology and levels of service. I would love for the makers of the game to fix some of these problems either through downloadable content or a new release. We need clearer thinking when it comes to transit and while this game doesn’t quite provide it, it very easily could.

[Alex Broner is a graduate student working on his Masters of Urban and Regional Planning at the University of Hawaii with an expected graduation date of December 2012. He is also an intern writer/researcher for the Sightline Institute.  His professional interests are in transportation, landuse, and urban design. Alex is passionate about creating enjoyable urban places where it is easy and safe to walk, bicycle, and take transit. His personal interests include cycling, science fiction novels, computer games, and dodgeball.]

Walkscore.com and the Lure of the Single “Score”

The Conservative Planner [blog site no longer active] has a thoughtful attack on WalkScore.com‘s methodology for calculating a simple “walkability score” for any neighborhood in America.  He’s found several examples where WalkScore has given a high score to a place that’s clearly hostile to pedestrians when viewed on the ground.  Continue Reading →

Good Question of the Week: Transfer Penalties

A frequent commenter on HT asks this in an email (the links are mine, not his):

On Second Avenue Sagas, one of the discussions went on a tangent that left me wondering about transfer penalties. If you need to walk from one station to another on the street to transfer, do the ridership models assign a higher penalty than if there’s an enclosed corridor between the stations? In addition, for systems that have faregates, is there an extra penalty for transfers that require exiting and
reentering?

Continue Reading →