The numbers game: Choosing the right metrics for transportation planning

This article was originally published by Mobility Lab.

Metro swipe - Kittner_20151021_7577 web


Last month, the Federal Highway Administration signaled it would follow California’s footsteps in encouraging moves away from Level of Service, a metric that encourages car-centered planning, toward ones favoring other, more beneficial ways people can travel.

These moves demonstrate the understated importance of measurements in forming how, and by what mode, localities encourage people to move in their daily lives. Choosing how to measure the performance of transportation projects is, in turn, a key factor in communicating the rationale and goals of those projects to the public. Clear, transparent data will help community stakeholders understand all the relevant factors and allow them to make informed choices regarding how they approach transportation in their lives.

Andrew Owen, director of the University of Minnesota’s Accessibility Observatory, led a discussion exploring this exact process at TransportationCamp DC, entitled “Choosing metrics for evidence-based transport planning.”

Level of Service, which measures traffic flow, has long been a popular choice for agencies, but it is car-centric and generally fails to account for other modes such as transit and cycling. Owen emphasized that LOS is not necessarily a bad metric, just the wrong one for cities’ goals. LOS grades plans on how well they would facilitate the quick movement of cars, operating on the implicit assumption that this is the best use of a road space. As the transportation landscape becomes more multi-modal, agencies must incorporate the new complexities of these systems into their goals, and effectively communicate them to the public. There is no such thing as “one metric to rule them all.”

With different metrics necessary for different places, Owen presented the concept of choosing metrics as a game, “trying them on” to examine what type of city or system each would favor. For example, a transportation system that yields high-miles-traveled-per-passenger might sound great in theory, but that metric would be maximized by long commuter routes where everyone lives outside the urban core. Another, opposite approach is to establish a desired outcome, and then select the right measurements to reach those goals.

An important consideration in either approach is the “decision tree.” The main question an agency addresses affects how it frames decisions. Agencies in the U.S. typically begin with “Where is a customer going?” while in Europe, planners begin with “How is a user getting somewhere?” These starting points can establish different values that lead agencies along different routes.

Perhaps most importantly, metrics should enable a conversation. If measurements are not actionable towards improving systems, then they are ultimately not very useful in initiating discussions. Indices with grades, like Level of Service, might be useful in starting conversations since they clearly communicate a value, but are not transparent enough to offer clear next steps for improvement. Much like talking specifically about how to choose metrics in the first place, the right measurements help transit planners and the public engage with each other.

Thus, agencies must consider their audiences when presenting their data. As metrics incorporate multi-modality, they become highly technical due to the very specific contexts they present. For example, it’s hard to directly compare cars and pedestrians the same way because they move on entirely different scales. Pedestrians can’t travel as far as drivers, so showing changes in each mode over time might better measure multi-modal goals. Meanwhile, the popularity of new shared-use options and connections – say, riding bikeshare to a Metro stop – are difficult to measure, as a loss in vehicle-miles traveled does not offer direct correlation.

In an effort to balance complexity and communication, there is a risk of choosing simple measurements and sacrificing accuracy rather than finding a simple way to explain a complicated concept.

However, having that conversation and communicating among stakeholders is essential – one of the TransportationCamp session’s main conclusions was that the only way to get a reasonable metric is to be clear about your values. When an agency works towards that, it can find the metrics that best suit the needs of people in the community.

This session was part of TransportationCamp DC 2016. For a more detailed look at what attendees discussed, click here, and see notes from the “VMT vs. LOS” session here.

Photo: Commuters tap into the East Falls Church Metro station (Sam Kittner for Mobility Lab, 

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