Vision Zero Boston: 25 mph default limit and open crash records
Boston pledged in 2015 to end traffic deaths by 2030. Using a 2016 state law, it cut the default limit on city-owned streets from 30 to 25 mph on 9 January 2017 and posts 20 mph in slow-street zones. Every crash Boston EMS attends since 2015 is published as a public-domain dataset and map, updated monthly.
Live
📅 since 2015
✔ Editor-reviewed
📊 Impact
The speed-limit change is one of the few urban limit reductions with a controlled evaluation. A peer-reviewed study in Injury Prevention compared speeds at Boston sites with control sites in Providence, Rhode Island, before and after: mean speeds fell 0.3 percent, which was not statistically significant (p=0.065), while the odds of a vehicle exceeding 25, 30 and 35 mph fell 2.9, 8.5 and 29.3 percent. The average driver barely changed; the fastest ones did. The programme's own goal is not on track — the city says Boston still sees 10+ traffic deaths and thousands of injuries a year.
🎓 Lesson
The measurable effect of a citywide limit change sat in the tail, not the mean: mean speeds barely moved while the odds of driving above 35 mph fell by nearly a third. And the rule stops where city ownership does — Boston's own notice tells drivers to watch posted signs on state-owned roads, which the 25 mph default does not touch.
Evidence🔬 Peer-reviewed
Scale🏙️ City-wide
CostTraffic calming funded at $15M in the enacted FY26 budget and $13M in the FY27 proposal
FundingCity of Boston capital and operating budget
Sources
↗ City of Boston — 25 in Boston (authority)Primary for the date and the scope limit. The default limit took effect 'January 9, 2017' on city-owned streets without posted limits. Also carries the jurisdictional caveat in the city's own words: 'This change only affects roads the City owns. Please pay attention to posted signs on state-owned roads.' The page does not name the enabling statute; that is sourced separately.
↗ M.G.L. c. 90 §17C — 25 mph in thickly settled districts (statute)The enabling authority. The Municipal Modernization Act of August 2016 let municipalities that accept §17C lower the statutory limit from 30 to 25 mph in thickly settled or business districts without MassDOT approval; Boston accepted it citywide, effective 9 January 2017. MassDOT's guidance page on speed limits in thickly settled districts covers the same mechanism.
↗ Hu & Cicchino, Injury Prevention 2020;26:99-102 (peer-reviewed)The controlled evaluation the entry rests on. Method: vehicle speeds collected 'at sites in Boston where the speed limit was lowered, and at control sites in Providence, Rhode Island, where the speed limit remained unchanged, before and after the speed limit change in Boston', with a log-linear model for mean speed and separate logistic models for exceedance. Result, verbatim: 'The speed limit reduction was associated with a 0.3% reduction in mean speeds (p=0.065), and reductions of 2.9%, 8.5% and 29.3% in the odds of vehicles exceeding 25 mph, 30 mph and 35 mph, respectively.' Neither the abstract nor the IIHS record states the number of sites. Note the authors are staff of the Insurance Institute for Highway Safety, an insurance-industry-funded body; the paper itself is peer-reviewed in a BMJ journal.
↗ IIHS — plain-language summary of the same study (research body)Second reading of the same numbers: 'After Boston lowered the default speed limit to 25 mph, the estimated odds of a vehicle exceeding 35 mph fell 29.3%', with 8.5 percent for 30 mph and 2.9 percent for 25 mph, Providence as control, measured around the 9 January 2017 change, at arterial, collector and local road sites.
↗ Analyze Boston — Vision Zero Crash Records dataset (authority, open data)The data layer, and the licence answer: 'Open Data Commons Public Domain Dedication and License (PDDL)'. Records run 1 January 2015 through 30 June 2026, updated monthly. The source is EMS, not police: 'Motor Vehicle Accidents (MVAs) provided in this dataset are Boston EMS incidents with a documented patient encounter that were identified as an MVA during the 9-1-1 call taking process, by crews on scene, or incidents where the injury cause is documented as related to an MVA', compiled by the Department of Innovation and Technology from the Computer-Aided Dispatch (911) system. The page also flags a break in the series: 'In June of 2024, Boston EMS transitioned to a new patient record system… Differences in MVA rates before and after June 2024 are reflective of this new reporting methodology and should not be interpreted as a change in motor vehicle incidents.'
↗ Analyze Boston — Vision Zero Fatality Records dataset (authority, open data)The other half of the split: fatalities are 'compiled by the Department of Innovation and Technology from the 911 system and verified by Boston Police Department', 1 January 2015 to present, monthly, also under the Open Data Commons Public Domain Dedication and License (PDDL).
↗ Vision Zero Crash Records Map — about page (authority)What the public map does and does not show. Records cover 'date, time, location, and type of crash for incidents requiring public safety response which may involve injuries or fatalities', but 'do not indicate the severity of specific crashes or whether medical care was provided'; 'Each incident is included only once regardless of the number of individuals involved'; the timestamp is when response was dispatched, 'not the crash itself'; and the city states errors may be present and the information may not be complete.
↗ City of Boston — Vision Zero (authority)The goal and the shortfall in the same place: the programme aims to 'eliminate fatal and severe traffic crashes in the City by 2030', while the city reports it 'currently experiences 10+ fatalities, hundreds of pedestrian and cyclist injuries, and thousands of driver injuries on city streets every year'. Also hosts the injury crash map and the by-mode dashboards.
↗ City of Boston — Neighborhood Slow Streets (authority)The 20 mph layer: traffic calming built in 15 neighbourhoods, where 'the speed limit on its residential streets will be 20 mph'. Piloted in the Talbot Norfolk Triangle in Dorchester and Stonybrook in Jamaica Plain in late 2017; renamed Safety Surge in 2023. No verified count of formally designated statutory 20 mph safety zones was found, so none is claimed.
↗ Streetsblog Massachusetts — Safety Surge announcement, May 2023 (press)What changed under the administration that took office in November 2021: the slow-streets programme was rebuilt as Safety Surge with more than $12 million in the FY24 budget, roughly 10 speed-hump zones and 25 to 30 intersection redesigns a year, prioritised on crash history and demographics.
↗ Streetsblog Massachusetts — FY27 budget cuts, April 2026 (press)The currency counterweight. Safety Surge falls from '$15 million in enacted FY26 budget' to '$13 million in FY27 proposal', and more than a dozen street-safety capital lines go to zero, including Roxbury Resilient Transportation Corridors ($32.5M to $0), Dedicated Bus Lanes ($13.5M to $0) and Commonwealth Avenue Phases 3, 3B and 4 ($13.5M to $0). Delivery, not just budget, is the issue: 'Boston's Streets Cabinet spent only $450,000 on speed humps in the past year – less than 10 percent of what the FY26 budget had proposed.'
↗ LivableStreets Alliance decade review, June 2026, via Streetsblog Massachusetts (independent)The only whole-programme assessment found outside the city; no municipal auditor review exists. The advocacy research group analysed a decade of crash data across Boston, Cambridge and Somerville, finding progress that was 'uneven at times'. On Boston specifically: 'Boston, by contrast, focused its resources on streets with the highest rates of injuries', citing Tremont Street, Centre Street in West Roxbury and the Common and Public Garden roadways. The report's standout is Somerville, with no fatal crashes since 2022 — not Boston.
↗ Boston Region MPO — High-Injury Network methodology (regional authority)Confirms what makes Boston's series unusual and where the city's writ ends. Regional high-injury analysis draws on MassDOT's IMPACT portal, whose 'crash database currently relies on information from police reports, but some cities, like Boston, also collect data from city EMS services'. It also records that roads on the network are owned variously by municipalities, MassDOT or the Department of Conservation and Recreation. No source gives a Boston-specific share of state-owned roads, so the entry claims none.
📎 Cite this project
1001 Smart Cities (2026). “Vision Zero Boston: 25 mph default limit and open crash records” — Boston, United States. The Smart City Atlas. https://1001smartcities.org/projects/boston-vision-zero/. Data: CC BY 4.0.
The underlying data is free to reuse with attribution — see the open data page.
🔗 Related projects
🇺🇸 Automated speed safety cameras (AB 645 pilot) · San Francisco
Both gains sit in the tail: SFMTA reports ~72% less 10-mph-plus speeding; Boston's 25 mph limit cut the odds of exceeding 35 mph by 29.3%.
🇺🇸 Automated school-zone speed cameras (Vision Zero) · New York City
New York reports 94% less speeding at its 2,000 camera sites; Boston changed the number on the sign and mean speeds moved 0.3%.
🇺🇸 Analyze Boston and the 2014 Open Data Executive Order · Boston
Boston's crash record sits on the same portal: every crash EMS attends since 2015, published monthly under a public-domain deed.
🇺🇸 Bluebikes: Bike Share Owned by Thirteen Municipalities · Boston
Another verified project from Boston.
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