I found where someone had already reblogged this on a model railroading forum. If they had already plugged it and took well over four miles to stop before they got to the steep part of the grade, then there was a much bigger problem with the air brake system that needed to be identified and resolved before they proceeded any further.

Assuming 107 cars at 131 tons each = 14,017 tons plus 5 engines at 200 tons is about a 15,000 ton train. On 2.9% you would need almost 870,000 pounds of braking force. SD40 series would have about 60,000 pounds per unit, so the expanded consist would only have a maximum of 300,000 pounds of dynamics or about 34% of the required amount, less as speed inceased above 20 mph. There is also the issue that dynamic brakes are usually restricted to not more than 240,000 pounds to prevent jackknifing. So adding a couple more units really didn't do much to compensate.

The mixed bag of units also suggests that the Orinoco system was not in use, so this and the weather I expect will be contributing factors. Since there were no deaths or injuries, I am guessing this will be an FRA investigation and NTSB is not involved.


December 8, 2013 8:32 PM

Here's the article: Trains News Wire EXCLUSIVE: Canadian National ore train
derailment was a runaway
Published: December 6, 2013
Two Harbors Tim Schandel
Ore cars from a derailed Canadian National
taconite train in Two Harbors on Thursday.
Photo by Max Medlin
TWO HARBORS, Minn. – The Canadian National ore
train that derailed in Two Harbors Thursday had air problems and was out of
control as it descended a 2.9 percent grade into Two Harbors, according to
sources familiar with the incident.

The 107-car train, U78982, had been loaded
earlier the same day at U.S. Steel’s Minntac Taconite Plant at Mountain Iron,
Minn. It was led by three units: DM&IR No. 407, an SD40-3 Tunnel Motor,
Bessemer & Lake Erie SD40-3 No. 909, and CN No. 6021, a rebuilt SD40-2. The
train crew first reported air problems as it approached Waldo, a junction four
miles north of Two Harbors. The crew reported to the dispatcher that they had
put their train in emergency for four miles and were still doing 40 mph. They
asked the dispatcher to line them directly into Two Harbors’ commercial
yard.

The crew was able to
bring the train to a stop just after Waldo and the beginning of the steep grade.
They told the dispatcher they would charge up their air and wait there, but one
grade crossing would be blocked. Since the crew was short of time, a pair of
units with a yard crew was sent out from Two Harbors to pull the train in. It
took about 45 minutes to couple the units and start moving again at about 12:55
p.m.

Now with DM&IR SD40-3 No. 405 leading, the train
made it about halfway down the grade when the crew called Two Harbors yard and
shouted their train was a runaway. It derailed and piled up as it entered the
yard.

There were four
crewmembers on board – the road crew and the yard crew from Two Harbors. Two of
them jumped as the train rolled into the yard and were injured, although three
feet of fresh snow may have cushioned their impact. Two others rode out the
runaway in the trailing units and did not have any injuries. CN spokesman
Patrick Waldron said an ambulance brought two people to an area hospital with
non-life threatening injuries.

The day before the accident the Two Harbors
area had received nearly three feet of snow, and the temperature at the time of the
incident was 9 degrees, so the weather may have been a factor in the
accident.

Railroad
spokesman Patrick Waldron declined to comment on the specifics of the radio
transmissions. He says, “All aspects of this incident remain under
investigation. We will not speculate on the circumstances nor what may have
contributed to or caused the derailment while that investigation is
continuing.”

According to
railroad spokesman Patrick Waldron, a total of 93 cars were involved in the
incident, 76 cars on the derailed train and 17 more loaded cars in the
yard.