Efficient Scenario Creation
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 Editor is separate from our GTFS editing tools; it works at a much less detailed level, focusing only on necessary information for accessibility analysis, not on details such as headsigns and other passenger information. Scenario Editor outputs scenarios in a format designed specifically to be applied rapidly to a transit network in our analysis tools, avoiding a time-consuming GTFS import process on every change to the scenario.
This allows us to create scenarios very quickly, allowing rapid feedback in planning processes. In a recent project, we laid out the backbone of a new transit plan in one afternoon and evaluated the results the next morning. Our goal is to reduce run times to the point where results can be seen within seconds of drawing a new line.
The Scenario
To demonstrate Scenario Editor, I mocked up a few proposed future transit options in the Washington, DC area. I added the Purple Line as well as rerouting the Blue Line subway through Georgetown and the north edge of downtown, as detailed in a post on local planning blog Greater Greater Washington.
Scenario Editor works using a suite of modifications laid on top of an existing transit system. The Purple Line is a brand-new line, so I used an “Add Trips” modification to create it. Using a map-based editor, I drew the stops. You can optionally have the lines you draw follow the street network; since the Purple Line runs largely in dedicated on-street right of way, I used this option to make drawing the line easier. I then specified a frequency and speed based on planning documents.
The Blue Line is an existing subway line that currently is interlined with the Orange and Silver Lines through downtown Washington; the proposal is to create a new, parallel subway downtown. This allows Metro to reach additional locations and increase the capacity of the system. To model this, I used a “Reroute” modification, which allows removing a section of a line and replacing it with a new section.
Finally, I increased the frequency on the 30S bus line, which traverses the District of Columbia from north to south, while retaining the existing routing and run times. In addition to adding routes, rerouting them, and changing frequencies, Scenario Editor can also remove routes or parts of them, and adjust speeds or dwell times (the time a vehicle stands at a stop while boarding passengers).
The Results
I then loaded the scenario into our analysis platform. I compared isochrones between the two systems; the image above shows how much further you can get by transit and walking within a 30-minute window from Georgetown under the new system.
I then performed a regional analysis where I evaluated the impact of the proposed changes on the number of jobs that can be accessed by people residing in every location in the region. We can clearly see the positive impact the Purple Line will have on job access for communities along its alignment. For instance, residents of Langley Park can access hundreds of thousands more jobs within 60 minutes of travel on transit. We also see increases in access in the H Street corridor east of Downtown, which is a major growth center in DC which does not currently have subway service. As expected, there is an improvement in Georgetown, west of downtown, a dense urban community that currently lacks rapid transit service. Finally, we see a general slight increase in access over much of the region, with pockets of very minor decrease due to the modified routing.
We are excited to announce the release of Scenario Editor. We are already using it in real-world projects in the US and Europe, and will be publishing case studies here shortly. If you’re interested in how Conveyal can help you with your planning processes, please get in touch. As with all of our products, Scenario Editor is open source.
Map data © OpenStreetMap contributors, some basemaps © Mapbox; transit data courtesy WMATA.
