Anti-collision technology is moving closer to reality on the MBTA’s Green Line, even if the full realization will take a bit longer than T officials told the public earlier this year.

The T will soon have enough equipment in place to roll out the first Green Line trolleys featuring on-board alerts about stalled vehicles or other obstacles on the tracks, more than 16 years after a fatal crash prompted federal regulators to recommend the system.  

A partial shutdown set to begin next week will allow the T to take another major step toward the “Green Line Train Protection System,” the first phase of which is now expected to be complete by next summer after a series of stops and starts. 

As one veteran official put it, the agency is “at a point where we can see the light at the end of the tunnel.” 

The technology relies on two primary features: equipment built into the cars and hundreds of “anchors” built alongside the tracks and platforms throughout the system. The anchors communicate with the on-board devices as trolleys move, allowing each vehicle to detect how close it is to others. 

In the first phase of implementation, Green Line operators will receive audible and visual alerts if the system detects a collision risk. The second phase, which is projected to be done in 2028, will add automatic speed control and braking. 

Crews will use the upcoming 15-day shutdown of the Green Line’s central trunk, primarily intended to replace the roughly 130-year-old wooden catenary wire trough, as an opportunity to finish installing anti-collision anchors underground. 

By the end of the year, T officials think they will have equipment in place for the Green Line Train Protection System from the endpoints at Union Square and Medford/Tufts through Kenmore Square, and also for the full D branch. Work to finish installation on the B, C, and E branches — the three other above-ground segments — will take place in the spring. 

The first trains using the new technology will roll out this winter, with full implementation set to be complete by the summer. 

“Each time the T introduces a trolley with the car-borne equipment between [December] and summer 2026, Green Line safety is enhanced more and more,” said MBTA spokesperson Joe Pesaturo. 

While the project moves ahead, the timeline has also been pushed back from prior public updates.