Enquiring minds want to know

Sitting in the middle of the tracks at Arlington Street Station (westbound) are about a dozen of these Kleenex-sized boxes spaced about 10m (30 ft) apart. Anyone know what they are?

Transponders for ATC? or Cab Signals?

CSRR573 wrote: ↑Mon Jun 06, 2022 4:02 pm Transponders for ATC? or Cab Signals?

Can't be cab signals. If its new it has to be with the new Green Line Collision Prevention System being rolled out this summer.

If it's old I want to say it is an Announcement transponder.

Could also be related to plans to rebuilt the trackways at Arlington and Copley to fix the issue of doors striking the platform.