Not the "T" proper, but a commuter train. It actually works very well.

The MBTA website (www.MBTA.com) explains their policy. Bikes are allowed on any train except designated rush-hour runs. I ride from rt128 station to Attleboro in the morning, definitely against traffic and the train cars are nearly empty. Same thing on the return.

The end of each car has a large area for wheelchairs, with fold-down seats too, so bikes are no problem. Sometimes there are several bikes, but space for one more can always be found. (MTBs with a humongously wide flat handlebar can be a real obstruction, but since I ride a road bike I can be a bike snob about it. ) Conductors have disgression to disallow a bike for space reasons but if you're not going with rush hour there isn't much reason for them to do so. Folding bikes are exempt from all the restrictions, but on a really crowded train that might still be a problem.

My biggest problem is having to make the train schedule. If I miss a morning train I'll miss a meeting at work. If I miss a train in the afternoon the next one doesn't come for three hours! I'll be spending the evening wandering around Attleboro with nothing to do.