The line from Lowell Junction to CPF-200 is the fastest and longest stretch of track Guilford owns (And in actuallity, Guilford only owns from the Mass state line east).
Aside from some permament speed restrictions in a few places, the line is rated for 40MPH freight. The reason you rareley see freights doing 40 is the lack of Head end boxes (HTD's). The FRA requires that any train operating over 30MPH must have working two way Telemetrey capablity. Guilford has less then 10 of these HTD's right now and they are almost always held for trains going from Fitchburg to Gardner that are 4,000 tons plus. And in many cases, even when a train is lucky enough to have an HTD, often it is too underpowered to reach 40 anyhow except for a few places with long downhill stretches. The Dover to Boston sand train DOBO/BODO uses NHN power which always has an HTD (and is never too heavy)and that is why that train is always seen running 40.
As for why the freight speeds are never raised above 40? A few reasons. As people stated, wear and tear on tracks and loco's and fuel is one, but the main reason is the track class system. The higher the class, the more money and time is required to maintain that class. There are standards that are associated for each class. These standards dictate inspection intervals, amount of ballast, tie grading, rail wear, etc. The vast majority of Guilford is class 2, which limits freights to 25mph. This is a cheap alternative to going to a higher class. Less money on materials and manpower. The line to Portland when it was upgraded in 2001 was supposed to be 132lb rail, but Guilford opted for 115 for cost savings. Not only for the rail cost, but the tie plates associated with it. The norm on virtually all the class 1's is 132lb rail and higher. 136 and 142 is very common on the heavy haul routes. 115 is almost never installed on major corridors and mainlines that see real tonnage. 115 is fine for passenger trains, but once you start running heavy freight on a daily basis with a dozen or more trains, 115 will not work for long. As for the 40mph speed for freight, that is actually plenty fast. Much of the class 1's track in the US is 40mph. Even where i run for CSX, 40 for manifest is the norm. Intermodal trains are allowed 50 and in some places, 60.
There would be almost no advantage at all to raising the speeds on that line to 50 for freight simply because the rest of the railroad is almost all at best 25. Combine that with no places to park multiple long trains (Lawrence offers pretty much ONE track to park a train more then 50 cars and not totally tie up the yard) and all you would do with raising speeds is create even worse bottlenecking of trains. The longer it takes for the larger trains to come down to Haverhill the more time that gives dispatchers to get other trains farther along. You need to keep things even as best as possible. As it is now, it almost always takes a minimum of 2 crews to get a train from Lowell to Deerfield. Many times 3 crews. There are only 2 places in Lowell you can park 60+ car westbound trains. CPF-NC and CPF-BY Meadowcroft St. And you can park one train at each location. The last thing they want is more trains showing up in a hurry. And going east is no better. Rigby yard is at best, half open. There is no night yard clerks and almost the entire westbound yard is out of service. Again, they dont want trains leaving Lowell and Lawrence and knocking on Rigby's door any sooner. As it is, they park trains at Rollinsford and Wells almost daily.
Unless the PAS deal truly brings the west end speeds up to 30 and 40 mph for the majority of it and then PAR fixes the tracks from CPF-312 going east to at least 25 AND they actually get some intermodal buisness out of Maine, i doubt you will ever see the speeds ANYWHERE on PAR ever go faster then 40.
