Most days I drive by a coal-fired electric generating station that receives coal via BNSF. Virtually always the train is pulled by two locomotives, one GE and one EMD. Is this just happenstance or is there a reason why the locomotives would be intentionally “mismatched”? This has occurred with many different engine pairs, so it’s not just the same setup coming back again.
Don’t know BNSF procedures - but railroads try to match power to the load. They may power a 13000 ton train differently than a 14000 ton train. ie. If a GE AC engine is rated 7000 tons and a EMD AC is rated 6000 tons over the territory - the most efficient use of power would be to use a GE & a EMD on the 13000 ton train and 2 GE’s on the 14000 ton train. Presuming that there is a choice of power available.
Thanks. That makes sense.
From the perspective of the train crew, does mixed power have any significant advantages or disadvantages over matched equipment?
There is most likely a 3rd motor dp’d at the rear of the train. As far as the mismatch its probably just coincidence.
Nobody mixes things up like CN does, and as a fan I appreciate that. It isn’t unusual to see the most modern engines mixed in with GP9s or even GMD1s… and even having the older power lead. It looks different, but thanks to CN for keeping it interesting.
Some railroads have “pools” of power used in various services. They may consider an SD70MAC and a C44AC as equivalent engines and so may allocate a certain number of each of those engines to serve in that pool. Any combination of those engines could be used because from the railroad’s perspective, in that service, they are the same.
Think of it this way, if you rent a mid-size car at the airport, the car rental company might give you any one of a dozen makes or models, but from the rental company’s perspective they are all “mid-size” cars.
Following is a short routing of a train from origin to destination and the ratings of various locomotive types over the various territories in the route
DEPT TIME ARRV TIME MILE SD40 SD50 C408 ES4D SD70 C4aC C44AH
MineX 1500 MineX 0259 0080 5700 6750 7400 7950 9400 9950 10800
MineX 0329 Locat1 0929 0095 5700 6750 7400 7950 9400 9950 10800
Locat1 1019 Locat2 1519 0090 2900 3450 3750 4050 4750 5050 5500
Locat2 1549 DEST… 0149 0176 4100 4850 5300 5700 6750 7150 7750
The software of this site makes formatting a table problematical
Locomotives will come up for service or inspection at varying times. Ratings notwithstanding, the railroad is going to use what’s available to get the job done.
Back in the day, seeing a mix of A units, B units, and GPs/SDs, etc was not unusual.
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Well, I think you did a pretty good job of it.
Yes, I’d like to be able to post tables, drawings and graphs to backup things. Maybe in one of their upgrades they’ll get to that.
Some railroads calculate tonnage differently than a chart.
Some use horsepower per trailing ton (hp/tt). Divide the total horsepower of the engines by the total trailing tonnage of the train. Different trains on different territories have different hp/tt requirements. A coal drag might have a .5 hp/tt while a premium TOFC train in mountainous territory might have a hp/tt of 4 while a premium TOFC on level territory might have a rating of 2.5.
Some use tons per powered axle (TPA). Each model of locomotive has rating of how many equivalent “powered axles” it has, that number being the tractive effort divided by 10,000. A C44AC would have 12 equivalent powered axles. Divide the total trailing tonnage by the total number of equivalent powered axles. Different trains on different territories have different TPA’s. A coal drag might be rated at 800 TPA while a TOFC train might be 200.
From Al Krug’s webpage on BNSF’s Dash 9 - 44CW - “C44” at: http://www.alkrug.vcn.com/rrfacts/dash9.htm
"Note 1: Notice that the Hp increases by 150% from throttle 1 to 2 and by 100% from 2 to 3. These huge increases make yarding trains at 10mph difficult. You must either constantly move the throttle up & down to maintain 10 mph or else apply independent brakes and work the power against the brakes making them hot. Perhaps GE had something with the 16 notch throttles on the 1960s era U25Cs."
- Paul North.
Just,
Much more important than builder/brand name, EMD/GE, is the type of traction motor, DC or AC.
Short story is that DC traction motors have a “Minimum Continuous Speed” below which operation at full power is likely to burn up the motor. Also, maximum adhesion is about 24%, at best.
AC motors do not have a MCS, and due to much better wheel creep/slip controls, AC units have adhesion ratings and Tractive Effort of about 150% of an otherwise identical DC unit.
What this means in practice is that in drag service, with units loaded to the limit on the ruling grade of the territory, AC units are preferred since they can grind along all day at 3-4 MPH. The same unit with DC motors would have a tonnage rating about 2/3 that of an AC unit, and tonnage rating would have to be figured at the MCS. Mixing AC and DC units in the same consist wastes the additional TE of the AC unit when it is operated at the higher speed necessary to protect the DC motors.
Mac