I've answered this question at least a few times via e-mail and Twitter DM, so that means it's clearly time for a blog post about it.
Many of you have noticed that eastbound trains go relatively slow when approaching the Framingham station. Why is that?
The simple answer is that there is a 15 mph speed limit from CP 22 (the signals just west of the Fountain Street bridge) to the Bishop Street grade crossing. The more complex answer (and the reason that adjusting that speed limit really wouldn't help) is that it is an artifact of the signalling system and the Concord Street grade crossing in Downtown Framingham. So no BIG fix is really (easily) possible - but the MBTA is now (as of December 2016) looking into some minor improvements.
Long explanation after the read more...
[You can learn a bit more about "CP" (Controlled Points) and "interlockings" in the glossary.]
As with all 'interlockings,' there are signals on either side of the interlocking to prevent trains from moving into the interlocking unless they have permission. The CP 21 signals for eastbound trains are at the east end of the Framingham station platform - between the Framingham station and Concord Street.
That is all a little confusing, but thank goodness we have a map where you can see it all.
That map also illustrates the west side of the Framingham station: CP 23 is near the Ashland-Framingham town line, and CP 22 is just west of Framingham station.
So, to get through Framingham moving eastbound from Ashland, a train goes from Ashland station, through CP 24 near Cherry Street in Ashland, through CP 23 near the Ashland-Framingham town line, under Winter Street, then past Nevins Yard (freight yard on north side of tracks). It then passes the signals at the west end of CP 22 and leaves CP 22 just when entering Framingham station. Within Framingham station, the train is between CP 22 and CP 21. Departing Framingham station, the train passes the CP 21 signal then crosses Concord Street. It leaves CP 21 about halfway between Concord Street and Bishop Street.
Now that we understand the physical arrangement of the area, we can take a look at the operational issues.
Normally, crossing gates that stop vehicle traffic at a railroad grade crossing are automatically activated when the train approaches. We're all familiar with this typical crossing gate operation.
At Framingham, for eastbound trains, this would be a problem - the crossing gates at Concord Street would need to come down as the train approaches the station - and vehicle traffic would be blocked for a longer duration while the train 'dwelled' in the station during boarding.
The solution for this is that the crossing gates at Concord Street are usually manually activated. The signal at CP 21 stays all red (stop) for eastbound trains entering Framingham station. The signal system is configured such that with the CP 21 signals showing stop, the crossing gates at Concord Street remain up, allowing cars to cross through downtown Framingham. Once the train wants to depart Framingham station, the engineer uses his radio to transmit DTMF tones (see the glossary) which initiate the crossing gates to come down. Once down, CP 21 displays some kind of proceed signal, and the train can depart.
Why does this matter? The signal system is an automatic block signal system (see the glossary again). That means that the signals are designed to convey information (and instructions) about the status of the NEXT track block and therefore the next signal. Also, the signal system was designed for long and heavy freight trains that require longer braking distances. So even though our commuter trains could brake in a shorter distance, the signal system has to default to the lowest common denominator from a safety perspective - and therefore create conditions that won't allow the heaviest train to violate a signal.
Therefore, with a stop signal at CP 21 for the Concord Street grade crossing, the previous signals 'up the line' display less than clear indications. This is why trains approach Framingham slower than other stations.
To be specific, approaching from the east:
At CP 24 (near Cherry Street in Ashland), trains get an Advanced Approach, which limits them to 45 mph.
At CP 23, trains get an Approach Limited (also 45 mph)
At CP 22, trains get a Slow Approach (15 mph).
Between CP 23 and CP 22, the cab signals 'drop' so that trains are at 15 mph approaching CP 22. The cab signals progress through Approach Medium (45 mph) to Approach (30 mph) and then Restricting (15 mph).
This also shows that a simple change in the speed limit won't help - the 15 mph speed limit between CP 22 and Bishop Street isn't even really a factor, since the signals are requiring that speed anyway.
There is one eastbound commuter rail train that doesn't stop in Framingham - the morning "bullet" or HeartToHub train. For that train, the dispatcher programs CP 21 to display a clear indication - meaning the train doesn't have to stop and manually activate the crossing gates at Concord Street. With a clear at CP 21, the crossing gates operate automatically when the train approaches. Having a clear at CP 21 allows the signals back through CP 22, CP 23, and CP 24 to also display clear - meaning the train can operate at the speed limit. So for this one train, the speed limit at CP 22 is the governing factor - even though the train is operating on 'clear' signals, it still must slow down to comply with the permanent 15 mph speed limit through downtown Framingham. My understanding is the speed limit is related to timing sequence of the traffic lights at both the Concord Street and Bishop Street grade crossings - because of the complexity of those intersections, more time is required to cycle through the light sequence to clear the crossing of car traffic. That means that more time is required from the train being detected until the train can come into the crossing - hence the requirement for a lower speed.
The signal progression for eastbound trains is factored into the schedules. Take a look at the transit (duration) times for trains between West Natick and Ashland. Westbound trains are able to transit that stretch at least 1-2 minutes faster than eastbound trains. For example, compare P508 with P521 - 16 minutes eastbound for P508 but only 15 minutes westbound for P521. DON'T compare P589 with P508 - that's not a fair comparison since P508 has much longer dwell times at all three stations since it has a much higher passenger load than the reverse commute P589.
This overall topic of eastbound signal progression through Ashland and Framingham was discussed during meetings of the Worcester Line Working Group, with a focus on the negative schedule impact for eastbound trains. It was noted that having a 45 mph speed limit (at CP 24) for a train that is three miles away from a stop signal is not really necessary for safe operations of commuter rail trains. This signal progression is an artifact of the arrangement that Conrail and later CSX implemented many years ago when there were many more (and longer, and heavier) freight trains on the line. In fact, we speculated that this signal progression was probably something that was not heavily studied when it was implemented, since there were no commuter rail trains going past Framingham (Worcester service wasn't restored yet) and freight trains were either destined for Boston or Framingham - none would be stopping at CP 21. So this particular sequence probably wasn't a big concern when the signal system was redesigned (which we believe was in the 1980's with the implementation of cab signals between Worcester and Framingham).
The MBTA has committed to investigating this signal progression with a focus on improving the speed of eastbound trains. At a minimum, it is expected that the signal system could be modified so that a Clear aspect (60 mph) could be displayed at CP 24. But it's not as simple as flipping a switch somewhere - there needs to be investigation of the effects of any change on the safety of the operations for BOTH freight trains and commuter rail trains, since CSX freight trains retain the right to transit this same path (and still do on a daily basis). There was no scheule announced for when they could implement this change, but the expectation is that it can be done prior to the Positive Train Control (PTC) project.