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.

However, in the case of public transportation, travel time is not the only cost…

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.

The bill establishes certain requirements for zoning codes in areas within 1/4 mile…

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.

Areas near transit in California could soon be open to denser housing development. Photo by Steve and Julie on Flickr, CC BY 2.0.

I don’t yet have an opinion on the bill. I’m…

At Conveyal, we provide tools that allow computing multimodal accessibility at a disaggregate, granular level across an entire urban region, allowing the creation of detailed maps that show (for example) the number of jobs every resident has access to within 60 minutes. These maps are very useful, particularly for evaluating the comparative effects of different future scenarios and seeing what areas of the city see benefits from a proposed service change. However, they represent a wealth of information, and sometimes it’s useful to summarize that information down to a single number, or just a few.

In the past, we’ve used…

Here at Conveyal, we use accessibility indicators — measures of how many jobs or other opportunities can be reached within a given travel time — in much of our analysis work. Our Scenario Editor tool allows creating public transportation scenarios and quickly seeing the impacts of these scenarios on the accessibility from different locations throughout a metropolitan region. However, when working with public transportation, there is no one number for accessibility. The number of jobs you can reach within, say, an hour, varies depending on when you leave your home. …

One of our main lines of work at Conveyal is analyzing future scenarios for urban transport systems. We have put a lot of time and effort into the measures and algorithms we use for this analysis, and can work at a high level of detail using GTFS data already produced by transit agencies. However, creating this data is laborious and is generally only done for existing transit systems. To allow us to perform this work efficiently, we are excited to announce our Scenario Editor tool. Scenario Editor is a map-based application that allows easily drawing modifications to transit networks.

Scenario…

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. …

Better Measures of Bike Accessibility

Here at Conveyal, we do a lot of transport analysis using accessibility metrics, which are simply measures of how many destinations you can reach in a given amount of time (for instance, if you live downtown, you might be able to reach 500,000 jobs within an hour’s travel time on transit). This is a measure of your potential access, without having to model individual choices about what commute someone might actually choose. …

Easy Extracts of US Census Data

Here at Conveyal, we work with US Census data a lot. Historically, retrieving this data has been a bit difficult, as you have to get the block level geometries from one place, data on demographics from another, and data on employment from a third. You then have to extract all the files and join them in GIS. It’s even more complicated if you hail from an urban area that encompasses multiple states (like the home of Conveyal: Washington, DC). …

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. …

Matthew Wigginton Conway

PhD student in Geography at Arizona State (focus on transportation). BA from UC Santa Barbara Geography.

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