Creating a Road Map of “Busable” Streets

Greater Boston’s makeup has changed significantly in recent years, with shifting demographics, emerging employment districts, increasing traffic congestion, and changing travel patterns. Meanwhile, up until recently, much of the MBTA bus network had not seen significant changes since the 1960s. To remedy this, the MBTA is launching the Bus Network Redesign, an initiative that aims to completely re-imagine the bus network to better reflect the travel needs of the region and create a better experience for current and future bus riders.

Re-imagining the bus network requires not only an understanding of where people are going, but also knowledge of what roads can get them there. On top of the Boston area’s complicated street networks, roads can be too narrow, rough, or steep to physically accommodate a 40-foot bus. Through their experience in the field, service planners have the knowledge of which streets buses can typically run on, but this information rarely exists in a format that is quickly available and spans the whole region. In an attempt to mitigate this data gap, OPMI created a road network map of the MBTA service area in which streets are assessed by their ability to accommodate a bus—a map of “Busable Streets.”

This single spatial map layer—built almost entirely on public data —uses multiple road characteristics to create a simple, three-level ranking: “busable streets,” “bus can travel if necessary,” and “bus travel not recommended.” Most of the factors needed for the rankings come from the Massachusetts Road Inventory, a MassDOT-maintained spatial dataset of roads in Massachusetts which includes information like the material of the roadway surface (e.g. pavement, dirt, gravel) and the type, or class, of the road (e.g. arterial, highway, local road). The Busable Streets layer also utilizes data of road grades (the slope or steepness of the street) from MassDOT and data of bridge height and weight restrictions from the National Bridge Inventory (NBI).

The map has two versions: one for fair weather and one for winter weather. The fair weather version incorporates road surface type, with lower rankings for irregular road surfaces like dirt and gravel; street width using road classification as a proxy, where local roads (typically more narrow) are flagged as “travel if necessary;” and height and weight clearances for bridges. The winter weather version adds road grades for icy conditions, with “if necessary” or “not recommended” rankings for roads with significant average slopes, especially on local roads (steep and narrow streets).

Below is an interactive version of the fair weather Busable Streets map, where “busable” streets are blue, “can travel if necessary” streets are grey, and “travel not recommended” streets are red. The map is centered around downtown Boston by default. To view more of the map, you can click and drag to pan around and zoom in and out using the plus and minus buttons at the top left of the map. The right-arrow at the top left also gives other navigation options. You can view this map full-screen by clicking the button at the bottom right corner.

Here is the winter weather version of the Busable Streets map. Predictably, many more streets are labeled as “travel not recommended”.

One of our biggest challenges in creating the dataset was making decisions regarding what the thresholds should be for what is considered “busable,” as we are the first transit agency (to our knowledge) to do a project like this. In determining bridge clearances, for example, we decided if roads were “busable” based on dimensions of the smallest and largest buses in the MBTA fleet. Decisions on road grades, on the other hand, were made using both snow routes—intentional re-routings due to winter weather—and service planners’ knowledge of where buses on the street tend to have trouble in snow and ice. Different thresholds required additional supplemental data sources and expert advice.

The Busable Streets map is intended to act as a base layer for bus routing, validating busable routes or flagging possible issues, rather than a filter that includes or excludes roads based solely on their ranking. Busable Streets is still missing information on underpass clearances, limited access streets, and other important factors, and it may never account for every possible consideration. The dataset also uses a proxy rather than exact measurements for street width, perhaps the most important road factor, but we hope future iterations will include measured street widths pending data availability. The dataset is ultimately meant to be a helpful complement to service planners’ knowledge, not a replacement.

Future iterations of the dataset could incorporate factors like parking, turn radii, street use restrictions, floodplains, and a gold-standard “highly busable” level with bus lanes and ADA-accessible sidewalks. Beyond the Bus Network Redesign, Busable Streets has the potential to support bus and rapid transit diversion efforts, inform conversations with communities on changes to their bus routes, and ultimately assist service planners in making data-driven decisions.