I'll set the stage and review the (planned) schedule:
P510 departs Worcester at 7:30 AM, passes Framingham 8:11 AM, arrives Boston 8:57 AM
P587 arrives in Framingham from Boston at 8:10 AM and turns to go back to Boston as P586 departing at 8:40 AM arriving Boston 9:34 AM.
P552 (#HeartToHub) departs Worcester 8:05 AM arrives Boston 9:07 AM.
Usually P510 uses track 2 at Framingham and P587/P586 uses track 1.
This AM, a freight train (probably B725 from Attleboro to Framingham) became disabled in Framingham station on track 2 right around 8 AM.
That left P510 stuck west of Framingham and unable to go anywhere since B725 was probably fouling everything since it would have been crossing track 1 to go up into Nevins Yard.
So they (dispatchers? "Boston Chief"?) took the P587/P586 equipment and renamed it P510 and sent it east from Framingham somewhat close to the P510 departure time. Once the original P510 equipment could proceed into Framingham, it entered on track 2 and was renamed P586, even though it already had all the P510 passengers from Worcester (to Ashland) on it. A track change announcement was sent out about the fact that P586 would board on Track 2 instead of its usual track 1. The new P586 using the original P510 equipment departed Framingham at about 8:45 and arrived in Boston about 9:40.
Tweets from passengers indicate that the P510-P586 switched equipment stayed in Framingham station for at least 10-15 minutes - around 8:30 AM to 8:45 AM. This appears to be for potentially two reasons:
1) Allow the P552 #HeartToHub to pass / leapfrog around it (which happened when P552 got to Framingham at 8:40 AM - a little later than its usual time of 8:30 AM)
2) Hold the old P510 equipment long enough so it wouldn't leave AHEAD of its new P586 scheduled departure time of 8:40 AM.
The P510 that originated in Framingham using the P587/P586 equipment was also held at CP 4 to allow the #HeartToHub to leapfrog around it. That appears to have been a minor delay.
Normally there are no leapfrogs needed on the schedule.
Not sure I can endorse this creative schedule maneuvering. The passengers on P510 between Worcester & Ashland definitely got the worst of this - a 40 minute delay. They still would have had a delay due to the disabled freight train, but it might have only been 10-20 minutes had they been allowed to 'remain' operating as P510. Leapfrogging P552 seems to be particularly unfair, since that train probably had a fraction of the passengers that P510 (or P586) had on it.
I also have to admit that it is sometimes unfair to be a Monday morning quarterback for these types of dynamic situations. It's possible they didn't know how long the freight train would be disabled and they made the best decisions possible given the information they had. At least they tried to do something creative.
More troublesome for you data nerds is how this will show up in the data metrics. Since they juggled some equipment names around, the data MIGHT reflect that everything arrived in Boston with a less than 5 minute delay. I'm not sure if they will use this manipulation of the data, but I hope not, since the P510 passengers between Worcester and Ashland were about 40 minutes late. If the data collection is automated there may be no way to manually correct it (or nobody may go in and do it).