Refurbished Green Line trolleys are returning to Boston after receiving significant work at a New York engineering facility.

“This is a great first step toward improving service on the Green Line,” said general manager Frank DePaola in a statement. “As these cars are re-introduced to the fleet, customers will notice gradual improvements in capacity and reliability.”

The Green Line fleet is comprised of 86 “Type 7” trolleys which were originally rolled out for service in 1986 and 1987. Nearly 30 years old and approaching the end their intended lifespan, the deteriorating trolleys are the focus of $104.4 million project preservation project.

Trolley system improvements include a replacement in the upgraded design HVAC, auxiliary lighting, flooring, seating, and insulation. Overhaul work focuses on each trolley’s structure, roof, exterior skin, door system, brake equipment, trucks, and propulsion.

The T says the first refurbished car is set to go back in service by early April, and about half of the entire fleet is penciled in to return by winter. Remaining trolleys are scheduled to hit the rails by the end 2016.