The MBTA Communities Law (Section 3A of the Zoning Act) applies to 177 municipalities in Massachusetts. Cities and towns must demonstrate compliance with the law by submitting worksheets and maps to HLC documenting that their zoning meets the requirements of the 3A regulations. The MBTA Communities District Atlas compiles information provided in those files to provide a comprehensive, accurate, and publicly available picture of zoning that satisfies the law's requirements. Learn more about the MBTA Communities program on HLC's website on the Multi-Family Zoning Requirement for MBTA Communities.
Compliant MBTA Communities districts, by the numbers
As of April 10, 2026, HLC has determined that 149 municipalities are compliant with the law and has issued letters documenting those determinations. While other municipalities are conditionally compliant or have submitted zoning that is currently under review, this page focuses on the communities that have completed HLC's compliance review process. Additional municipalities will be added to the Atlas as they are determined to be compliant.
These 149 municipalities met their compliance requirements with a combined 468 zoning districts. Some cities and towns met the requirements of the law with just one or two districts; others submitted over a dozen different districts and subdistricts to demonstrate compliance. You can explore all of these districts through the MBTA Communities Atlas interactive webmap.
The compliant MBTA communities identified 28,819 assessors parcels on which their MBTA Communities zoning applies. In some cities and towns, the districts cover hundreds or even thousands of parcels; other towns were able to demonstrate compliance through zoning that applies to only a handful of parcels or even a single parcel. The interactive webmap shows each one of these parcels with information about the size, owner, current use, and other important attributes.
Interpreting multi-family unit capacity numbers presented in the atlas
Users of the Atlas will encounter information on the modeled multi-family unit capacity of each parcel. Each MBTA community is required to demonstrate a different minimum multi-family unit capacity based on its 2020 housing stock and transit service type. Unit capacity is calculated by estimating how many homes could be built on each parcel in a given district. These estimates are generated using a standardized compliance worksheet developed by HLC and filled out by the municipalities. The worksheet incorporates information about zoning rules, developable lot area, and other factors to estimate gross unit capacity, assuming each parcel is built to the zoning's maximum possible density regardless of existing buildings. Due to the sheer number of parcels, these estimates can't account for specific constraints that may limit development on a given parcel. Therefore, unit capacity estimates should be treated as an upper bound of development potential. Conversely, some developments may exceed this estimate by combining multiple parcels. Unit capacity is only one of several key metrics used to determine MBTA communities compliance. HLC encourages users of the Atlas to interpret multi-family unit capacity numbers in the context of this specific regulatory function, rather than as a comprehensive estimate of development capacity or a projection of future housing production.
Conclusion
HLC is proud to be publishing this comprehensive and authoritative dataset about zoning districts pursuant to the MBTA Communities Law. The Healey-Driscoll Administration is committed to monitoring and evaluation of major policy initiatives to facilitate continuous improvement. The Administration also believes in transparency and values the contributions of the Commonwealth’s researchers and journalists to our public discourse. This new dataset can help builders seeking new development opportunities; researchers looking to assess the impact of the law; planners who want to better understand potential growth; and stakeholders who want to know what the law means for them.