Around 1:15pm the Bridgeport ECC received a call from MTA regarding a possible locomotive fire at the Connecticut Ave & Bishop Ave railroad overpass. Bridgeport dispatched a Signal 29 (Alarm of Fire) “Frank” assignment. I do not recall the full assignment. Battalion 2 on arrival reported MTA employees using dry chemical extinguishers in one of the passenger cars and had Engine 6 bring theirs up. MTA is investigating the cause at this time, but preliminary reports suggest an issue in the brakes. On arrival, I found Engine 6, Ladder 6, Battalion 2, and Safety Officer 1 on scene along with BPD and MTA PD.