February 26, 2025

Asserting coefficients and parameter scaling

In travel demand modeling, it is somewhat common to “assert” coefficients rather than estimating them from data. I think most modelers would agree that this is a process that should be avoided when possible, but that is sometimes necessary—for example, to model mode choice for a mode that does not exist in a region yet. For example, the following guidance from the Federal Transit Administration appears in NCHRP 716:

June 19, 2020

Regular $2, for you $3: when a discounted transfer is not a discount

Often, there are discounts when transferring between transit vehicles. But in some cases, using a discounted transfer could cost you more.

April 30, 2019

How transit fares affect accessibility

Accessibility metrics are increasingly being used for planning, with planning agencies measuring what opportunities the transportation network connects residents to. A common accessibility metric is the “cumulative opportunities” metric, which measures how many opportunities can be reached within a given travel time budget—these opportunities could be jobs, grocery stores, or even abstract space. Furthermore, accessibility is frequently invoked in discussions of just transportation systems. Karel Martens and Rafael H.M. Pereira both argue that just transport systems should provide a baseline level of access to all individuals.

January 13, 2018

Identifying high quality transit corridors

In my previous post, I analyzed the effects of a proposed bill in California that would dramatically upzone areas around transit stations, allowing for increased housing production, albeit potentially creating opposition to transit projects. In that post, I presented a map showing the area potentially affected by the bill, and I promised a further explanation of the methodology used to create it, which I present here.

Areas in Los Angeles potentially affected by SB 827. Data © LA Metro, Metrolink, OpenStreetMap contributors.

The code used in the analysis is open-source and available here. It is written in Python 3, using a Jupyter notebook.

January 8, 2018

Will Rezoning Around Transit Stops in California Undermine Support for Public Transit?

A proposal under consideration in the California State Senate would prevent cities from limiting residential density near public transit. SB 827, proposed by state Senator Scott Wiener, prevents cities from enforcing zoning ordinances with housing density maximums, sets minimum standards for height limits, and abolishes parking minimums, in the areas around “high connectivity” transit stations and along corridors with transit service more frequent than every 15 minutes. This would allow the construction of much more sorely-needed housing in California. However, it could also increase opposition to future public transit projects.

January 24, 2016

Moving to Medium

Here we are early in 2016, and I decided it was time to revisit how I publish my writing. I’ve had a blog for a while, but I’ve recently been realizing that the future is social, and my ideas would be easier to share if they were hosted on a social platform. With that in mind, I’m going to put new posts exclusively on my Medium profile:

Matthew Wigginton Conway

For those that prefer an old fashioned web address, you can still visit blog.indicatrix.org, which will redirect you to Medium.

January 24, 2016

Pareto Efficiency and Urban Planning

Urban planning is the process by which society decides how our cities and regions will develop in the future. As anyone who’s been involved in a planning process can tell you, it is a very difficult field. I argue that the reason for this is because there are no easy wins in planning; we cannot improve outcomes in one dimension without making them worse in another.

The theoretical underpinning of what I’m describing is known as Pareto efficiency. The gist is that you have multiple measures which you would like to minimize or maximize. A scenario is Pareto-efficient when you cannot improve any measure of interest without making another measure worse.

September 12, 2015

Millenials and Communal Living

A Citylab article from a few weeks back observes that the rate of household formation among millenials remains low. A large proportion of millenials are still living with their parents, certainly a sign of economic hardship. However, the article also notes that it is “alarming” that when millenials eventually do leave their parents’ households, they often do not form new households but instead live with other adults. The article views this as a sign of economic malaise, which indeed it is, but fails to note that there are concomitant social changes that drive millenials to live together, independent of economic concerns.

February 26, 2015

Game Theory and Snow Shoveling

My adopted city of Washington, DC, is shoveling out from under some of the last snow of the season. At the same time, we’ve just enacted a law that levies fines on residents who don’t clear their sidewalks, after years of debate.

There’s a very good reason to fine property owners for not shoveling their sidewalks. Snow shoveling is a what’s known as a multi-player prisoner’s dilemma. If everyone shovels, everyone is better off (because they can get around more easily, don’t face the danger of falls, don’t have to pay extra cleaning bills due to muddy/salty pant cuffs and skirt hems, &c.). However, any one person is better off if they don’t shovel, because they’ve saved time (I actually like shoveling my sidewalk, but let’s assume that the utility for shoveling is uniformly negative). Each individual isn’t affected much by the state of their own sidewalk, but rather by the state of everyone else’s.

December 26, 2014

Dijkstra's Algorithm Visualization in the Browser

Dijkstra’s algorithm is a method for finding the shortest path through a graph with non-negative edge weights. It is a relatively efficient algorithm, and is guaranteed to find the shortest path (unlike some heuristic algorithms). It’s a fairly simple algorithm, but also one that can be difficult to wrap one’s head around. Descriptions abound on the Internet, and there are a number of videos, and even a few interactive demonstrations, but I thought there needed to be a demonstration that was interactive, worked in modern browsers without a plugin, used a non-trivial graph, and was open source. So I wrote one. A prose description of the algorithm is there; I hope it’s easier to understand with the interactive component. Visualizing algorithms tends to make them easier to understand, as observed by Mike Bostock.