The MBTA Communities Act and Section 3A Zoning in Greater Boston

What is the MBTA Communities Act?

The MBTA Communities Act is a Massachusetts law, codified as Section 3A of the state Zoning Act, that requires every community served by or adjacent to the MBTA to zone at least one district of reasonable size where multifamily housing is permitted as of right. That housing cannot carry age restrictions and must be suitable for families. The district must allow a minimum of 15 dwelling units per acre and, where transit applies, sit within half a mile of a commuter rail station, subway station, ferry terminal, or bus station. It applies to 177 cities and towns, with Boston itself exempt.

One point that gets misunderstood constantly: the law does not require anyone to build housing. It only requires the town to write zoning that would allow it by right. The "unit capacity" figures you hear are zoning capacity, not a construction mandate.

Is the law actually being enforced?

Yes, and that question is now settled. In January 2025 the state's highest court ruled in Attorney General v. Town of Milton that compliance is mandatory and that the Attorney General can sue to enforce it. In June 2025 a separate challenge arguing the law was an unfunded mandate was dismissed. Towns that fail to comply lose eligibility for major state funding sources, including MassWorks, the Housing Choice Initiative, and the Local Capital Projects Fund. As of the state's April 2026 compliance list, 149 communities had been formally determined compliant.

What does 3A mean for my property in the corridor?

If your parcel sits inside or near one of these new districts, you may now be able to build or convert to multifamily by right where the old zoning would have required a special permit or blocked it entirely. That can meaningfully raise a property's development potential and its value. The flip side matters too: if you are buying, whether a parcel falls inside an overlay district is now a real factor in what you can do with it and what you should pay. This is exactly the kind of analysis we run for owners and investors before they buy or sell.

A concrete example. A typical Belmont two family at the edge of the Belmont Center overlay was previously zoned to allow a maximum of two units. Under the adopted overlay, that same parcel may now support a small multifamily building of four to six units by right at the minimum 15 units per acre density, depending on lot size and the town's specific district rules. The value implication can be meaningful. The same lot that was worth roughly $1.4 million as a two family rental might be worth $1.6 to $2.0 million to a developer or investor acquiring it for its by right multifamily potential, depending on configuration, market timing, and the specific overlay parameters. Not every parcel benefits equally. Some lots are too small, others sit just outside the overlay boundary, and the actual permitted density depends on the town's specific zoning text. But the change in development rights is real, and many owners do not realize they hold it.

For a deeper analysis of how Section 3A is reshaping land value across the entire 13 town MBTA corridor, including the 53,121 unit total zoning capacity and the corridor wide pipeline, see our MBTA 3A property value analysis.

Which corridor towns have adopted 3A zoning?

Every town in the PHRG corridor is now compliant with Section 3A, though the category, the required capacity, and the mechanism each town used differ. The table below shows where each of the 13 corridor towns stands. Always confirm a specific parcel against the town's adopted district map before acting.

All capacities below are from the official EOHLC June 2025 capacity calculations.

Total minimum multifamily zoning capacity across the 13 corridor towns: 53,121 units.

How do I find out if my property is in a 3A district?

Check your town's adopted 3A overlay map, which each compliant community publishes, or look it up through the state's Executive Office of Housing and Livable Communities. Because the maps are parcel specific and the rules differ by town, the fastest path is to send us the address. We will tell you whether it falls in an overlay, what that allows, and what it means for value.

Written by Ethan Piani-Hohmann, broker and founder of PH Realty Group, a Greater Boston brokerage focused on multifamily and investment property. Based in West Newton, Ethan has worked with owners and investors across the 13 corridor towns covered here for several years, with active deal flow in Newton, Watertown, and the Mass Ave and Broadway corridors of Arlington. PH Realty Group has tracked MBTA Communities Act compliance for the full Greater Boston corridor since the rapid transit deadline in 2023 and updates this guide as the state's compliance list changes. Massachusetts Real Estate Broker, License #9630770-RE-LC. Last updated June 2026.

Find out what Section 3A means for your property. Send us the address for a free overlay and value assessment, or read our MBTA 3A property value analysis for the corridor wide value picture.