Green Line Train Protection System
Boston's Green Line light rail has no system that enforces its signals or speed limits — operators simply obey them. The MBTA is fitting ultra-wideband positioning that warns of overspeed and closing trains. The NTSB recommended collision avoidance in 2009; a 2019 contract collapsed and was re-let to Piper Networks for $112.5M in 2025. Automatic braking is due 2028.
In build
📅 since 2019
✔ Editor-reviewed
🎓 Lesson
A safety recommendation is not an order. The NTSB recommends and cannot compel; the FTA, a different agency, is the one that issued binding directives to the MBTA in 2022. Seventeen years after the NTSB asked for collision avoidance on the Green Line, no train is protected by it yet.
Evidence• No measured figure
Scale🗺️ Regional
Cost≈US$112.5M Piper Networks contract (2025), after an US$83M contract awarded in 2019 to BBR/Stadler was abandoned in 2024 with US$18M paid
FundingMBTA capital programme
Sources
↗ MBTA — Green Line Train Protection System (operator project page)Authoritative description of what the system does and does not do: 'The system monitors every train's speed and location in real time and will alert operators if a train is moving too fast or getting too close to another train.' Phase 1 'adds audible and visual alarms to alert operators about speed violations and avoid collisions'; Phase 2 'adds additional protections to help prevent passing stop signals and support safe operation in temporary slow zones.' The operator never claims the driver is replaced.
↗ MBTA — Essential work across the subway and commuter rail system in 2025 (operator, 16 January 2026)Sentence-level source for build progress and schedule: 'More than 930 GLTPS anchors installed', 'nearly 68,000 feet of messenger wire installed', 'more than 200,000 feet of cable have been installed within the track area', and 'more than 330 additional anchors along the B, C, and E branches in spring 2026'. Scope covers the signalized branches from North Station to Medford/Tufts and Union Square, the core tunnel from all branch portals to North Station, and the D branch from Riverside to Fenway — which establishes that the Green Line Extension is included. Schedule: 'Following a testing and data collection period over the next several months, the MBTA anticipates Phase 1 of GLTPS will be operational in summer 2026.'
↗ MBTA Board of Directors — GLTPS-2 Procurement staff summary, 25 February 2025 (operator)Contract source: award to Piper Networks not to exceed US$112,529,564; technology described as 'Piper's Cenelec SIL-4 Ultra-Wideband positioning technology to localize trains operating both at grade and in the underground central subway areas'; three deliverables — collision avoidance, overspeed protection, and full territory response to signals and speed changes. PDF; could not be rendered by the review tooling, figures verified through the search index of the same document and corroborated by the Boston Globe and CommonWealth Beacon reports listed below. Note that a SIL-4 rating is a design certification, not a result.
↗ NTSB — Collision of Two MBTA Green Line Trains, Newton, 28 May 2008 (RAR-09/02)The fatal accident behind the recommendation: a westbound train travelling about 38 mph struck the rear of another near Waban, killing operator Ter'rese Edmonds. Probable cause was the operator's failure to comply with the controlling signal indication, consistent with an episode of micro-sleep; 'contributing to the accident was the lack of a positive train control system that would have intervened to stop the train and prevent the collision.' Source for the precise defect: Green Line trains 'do not incorporate systems such as trip stops (mechanical arms or electrical inductors that slow or stop a train if the operator fails to respond)'. Recommendation R-09-008 was addressed to the Federal Transit Administration, not to the MBTA — the NTSB recommends, it does not order.
↗ WBUR — In final report, feds fault driver, overdue safety features in 2021 Green Line crash (5 January 2023)Carries the NTSB's finding on the 30 July 2021 Commonwealth Avenue collision in the Board's own words: 'Had such a system been in place at the time of the accident, this collision would have been prevented.' Probable cause was the operator's sudden acceleration and 'loss of situational awareness'; 24 passengers and three MBTA workers were taken to hospital. Also records the MBTA target current at that date — completion by June 2025, itself a two-year slip.
↗ NTSB — Collision at East Somerville station, 9 February 2025 (investigation RD25FR007)The most recent accident of exactly the type the system is meant to stop, on the newest section of line: at about 12:22 a.m. a train travelling about 32 mph entered a 25 mph zone, passed a red signal and entered the 10 mph station zone before striking a stationary out-of-service train. Six people were injured and the MBTA estimated US$6.6 million in damage. Preliminary report published 6 March 2025. It happened seventeen days before the board approved the Piper contract.
↗ Boston Globe — MBTA scraps Green Line crash prevention contract, will start over (7 June 2024)Source for the abandoned first attempt: an US$83M contract awarded in 2019 to the German firm BBR, later acquired by Stadler, on which the MBTA had paid about US$18M without seeing meaningful progress; the agency terminated it in June 2024 and moved to recoup the money. Paywalled; the figures were verified through the search index of the same article and are consistent with the February 2025 board procurement.
↗ CommonWealth Beacon — The T will soon roll out Green Line trolleys with anti-collision techIndependent reporting that keeps the two phases apart: Phase 1 gives 'audible and visual alerts if the system detects a collision risk', Phase 2 adds automatic speed control and braking and is not anticipated on trains until 2028. Also the source for the slip — officials first said Phase 1 would be complete by December 2025 and then moved it to mid-2026, against a contract deadline with Piper of March 2027.
↗ Federal Transit Administration — Special Directive 22-12 and the MBTA Safety Management InspectionIncluded so the two federal bodies are not conflated. The FTA — which can compel, unlike the NTSB — conducted its Safety Management Inspection of the MBTA between 14 April and 30 June 2022 and released the report on 31 August 2022 with 20 findings, accompanied by four Special Directives to the MBTA and one to the Massachusetts Department of Public Utilities. That is a separate action from the NTSB's 2009 recommendation and did not create this project.
↗ MBTA — Track Improvement Program (operator)Context for the wider safety crisis this project sits inside, kept to one dated figure: the programme removed more than 220 speed restrictions and replaced more than 250,000 feet of rail, clearing the last track-related slow zones in December 2024 after 23 planned closures across four lines during that year. Operator-reported; used for scale only, not as an impact figure for the train protection system.
📎 Cite this project
1001 Smart Cities (2026). “Green Line Train Protection System” — Boston, United States. The Smart City Atlas. https://1001smartcities.org/projects/boston-green-line-train-protection/ (last verified 2026-07-26). Data: CC BY 4.0.
The underlying data is free to reuse with attribution — see the open data page.
🔗 Related projects
🇺🇸 Muni Metro Advanced Train Control System & Its Replacement · San Francisco
San Francisco's tunnel has driven trains since 1998 and is replacing that; Boston's Green Line still has nothing enforcing its signals.
🇺🇸 MTA Subway Communications-Based Train Control · New York City
New York has been retrofitting signals line by line since 2009; Boston's Green Line is due its first alarms in 2026 and braking in 2028.
🇯🇵 Nanko Port Town Line (New Tram) Driverless Guideway · Osaka
Osaka put crews back aboard after its 1993 runaway; Boston's Green Line never had automation to lose — its 2008 crash killed the operator.
🇨🇦 Toronto Subway Automatic Train Control Resignalling · Toronto
Toronto shows the far end of this road: a legacy line resignalled to run itself between stations, seven years late.
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