Analyzing Network Effects with Conveyal: A Sol(ar) Case Study in Madrid
Disponible en español aquí.
Editors Note: This guest post is authored by Juan Btesh, an urban mobility consultant based in Madrid. Juan recently completed a masters thesis at the University of Porto, “Measuring Equitable Access to Public Transport,” and now works with a range of governments and private stakeholders.
If the Sun were to vanish suddenly, the Earth could drift into a void, freeze to absolute zero temperatures, and suffer a catastrophic meteor-like impact. But it could also be drawn to an alternative centre of gravity, interacting with other cosmic bodies and finding a new equilibrium.
What would the Sun be in the transport system of Madrid? The “Sol” multi-modal station is located in the heart of the city and is the most utilised metro station of the network with 22 million annual passengers. Also “Sol” is Spanish for “Sun” so everything points to Madrid as an example heliocentric transport network.
So what if the “Sun” disappeared? Sometimes a metro station can become temporarily unavailable due to maintenance, renovation or accidents. Removing Sol would impact all the different destinations and opportunities that the station allows access to and prevent people from connecting between different lines, as it serves as an important transfer point in the city.
Removing Sol looks like the Earth drifting-into-the-void scenario. For anyone familiar with Madrid’s Metro network, a mental map of the first-order effects of removing Sol is easy to draw. Passengers who start their journeys at the station would see their access orbits collapse inward. But effects in other parts of the city might be hard to visualize just based on intuition, given the complex structure of the multi-modal metro and street network.
One way to prepare for different eventualities is quickly sketching scenarios and evaluating the consequences — similar to how rocket scientists simulate a wide range of situations when designing launch vehicles. Conveyal is a web-based analysis tool that allows measuring access to opportunities with different transport scenarios. It allows applying a range of easy-to-use modifications to a multi-modal transport network, such as removing a station, then quickly comparing accessibility results between the modified network and a baseline.
A 15-minute isochrone is drawn comparing baseline scenario (blue) and the edited scenario without Sol station (red). As seen, the reachable area is considerably less in the edited scenario. If we were to pick a type of destination and measure access to, let’s say, education centers (seen as dots on the map) we would conclude that removing the station would reduce access to educational opportunities from Sol by 65% (218 vs. 77 education centers reachable in 15 minutes).
As an example of impacts on other parts of the network, consider Sevilla Station along Metro Line 2 as an origin for isochrones. Even though the origin is just one stop away from Sol, accessibility in areas reached by Line 2 that need no transfers (North and Northeast) remains unchanged. Opportunities located along lines 1 and 3 (South and Northwest) where transfers are needed, are no longer accessible.
To evaluate the impact on the whole city, rather than selected origins one-by-one, we can measure accessibility using Conveyal’s batch regional analysis and see how a sudden removal of Sol Station affects Madrid.
Accessibility is not only greatly reduced in the area around Sol but also in scattered areas around Madrid — particularly in areas served by metro lines 1, 2 and 3, which are the ones with transfers at Sol in their routes.
A similar analysis could highlight areas that might need shuttles or other alternative service options in contingency plans for station shutdowns across the network.
Being realistic, the idea of shutting down Sol Station is hard to conceive as an intentional measure and can only be thought as temporary, in case of an accident or due to urgent construction/maintenance. In any case, rapid, detailed accessibility analysis can help build an understanding of network effects, revealing orbit-like contours and multi-modal centers of gravity, and informing resilience strategies for handling unexpected disasters— though perhaps not a cosmic catastrophe or meteor strike!
