By Howard Monroe

PHILADELPHIA (CBS) — SEPTA’ s Route 15 trolley is being replaced with buses this weekend. The transit agency says the vehicles will get a heavy-duty overhaul during the time off. But some transit advocates are crying foul.

SEPTA says they need over a year to make the repairs. But transit advocates say they’re concerned the trolleys will never come back.

“It could happen but I don’t see that. That’s usually what they say. They’ve promised to bring back other trolley lines and they never do it. It’s just what they say,” trolley activist Scott Maits said.

Maits says he doubts SEPTA’s Girard Avenue Line will ever see a trolley again but SEPTA says there’s no need to worry.

“Our board chairman yesterday and our general manager both stressed that they are behind the repairs to the Route 15 trolley and getting them back in service as quickly as we can,” said SEPTA General Manager of Operations Scott Sauer.

The trolleys on Route 15 date back to 1947. They were most recently rebuilt in 2002.

Sauer says each car has its own problems but says some have structural issues and others need air conditioning and heating updates.

“They’ve had different reliability issues over the years that our maintenance crews have stayed on top of and tried to keep them in service,” Sauer said.

SEPTA says of the 18 trolleys in the fleet, only four are operational.

While repairs are being done, the trolleys will be replaced by buses. SEPTA says the trolleys will be out of service through 2021.

“The fact that it’s a historic trolley, you get used to seeing the trolley from time to time but I guess it’s a give and take. They have to be serviced,” one woman said.

SEPTA says they don’t know how much the overhaul is going to cost. They say engineers need to look at the problems first.

However, the last time the city rebuilt the entire fleet, it cost $88 million.

Bus service begins Sunday.