With four miles of one track out of service due to bridge construction, the MBTA is tossing their current schedule out the window for a new one to start on April 7. Only 34 percent of morning rush hour trains were able to adhere to it in February anyway.

"I think better information for the public is needed because standing on a platform not knowing whether their train is going to come or if it's not going to come is just not fair," said Pamela Bush, a member of the On The Move Coalition who also sits on the T Oversight Committee.

Bush and others on the committee queried general manager Dan Grabauskas and other T executives on the problems Monday night at a committee meeting.

"They don't prioritize the Fairmount Line because they use it for so many other trains," said Bush in a phone interview. "I asked them if there is any other way to get the trains to the rebuild yard."

There are 40 scheduled Fairmount Line trains each day, six Franklin Line trains that bypass Dorchester stops and 11 trains that travel to a rebuild yard at Readville for daily maintenance, according to rail operations manager John "Jody" Ray. CSX, the freight carrier, also runs the occasional train or two on the track on an irregular schedule.

"Just the scheduled trains would be difficult," said Ray, adding that the T has shifted as many empty trains to the northeast corridor - or Attleboro Line - as is possible.

The new schedule will take effect on April 7, and has only subtle differences for riders compared to the one created late last year. Inbound trains will not stop in Readville at 8:16 a.m. or 4:18 p.m., and that particular afternoon train will run ten minutes earlier. Coming back to Dorchester, a few morning trains will run between two and five minutes earlier and the 7:05 a.m. train to Readville only will be eliminated.

The difference that make it a scooch more doable for the T's timekeepers is replacing one or two Fairmount trains with Franklin trains that usually pass Dorchester stops, but will now stop to pick up passengers. Nevertheless, MBTA officials are not guaranteeing a return to the 70 or 80 percent on time percentages Fairmount Line passengers have gotten used to in the past.

"To do this amount of invasive construction there is no way around it," said Ray. "The new schedule will help. We can get the on time performance improved but we also know the limits of sending this many trains through a single track. We know that the trains have to run on time for the ridership to grow, that's the goal every day."