Coal Train Startup Questions

Here in Denver, Colorado we have a lot of coal rolling through. Today I saw a 1.3 mile-long BNSF train starting up from a standstill. The two front end units weren't in run 8 as they passed me, but by the time the two units shoving from the rear went by they were in full power. (Well, I am assuming that they were in full power).
I was wondering about two things.

First, does anyone have an idea of how long it can take (or how far) for a loaded coal train to get to speed on fairly level ground?

Second, at what point do they notch it up to run 8 - once they pass the wheel slip speed?

Thanks.

You're asking a question nearly impossible to answer with any accuracy.

What do you mean by up to speed? Up to speed might be crawling at Restricted Speed or 60 MPH depending on territory speed limit, signal indication, best speed for tonnage/grade, or any number of other factors. How heavy is the train and how much power do you have? Two GP9s or five AC44s? Good traction control systems on a DC engine or advanced AC spin control? Are the engines in good condition or are they tested low/de-rated, blowing fire out the stack or have fuel rack problems? Even 1.3 miles is still not enough info. Are they 100 ton cars or 130 ton cars? There are plenty of other factors too.

Wheel slip speed? You can get wheel slip in any notch. What are the rail, weather and locomotive conditions? Cold/hot, wet/dry, leafy, bug coverage, presence of lubricators, well maintained engines or junk, stick rail or CWR? Hard curves or tangent? You might be in run 8, dumping sand and moving at less than one mile an hour, with or without wheel slip. And wheel slip in practical terms means something different than design terms. Most all modern engines have a certain amount of wheel slip built in before they will indicate a slip. To the designer the engine is slipping any time wheel speed exceeds ground speed, to the locomotive engineer the engine isn't in wheel slip until it goes to free-wheeling, indicates, and he has to take action.

Without knowing the territory or what the train you saw was up against, I can only guess that they started on a less than favorable signal or speed restriction and by the time you saw the helpers they had better and had throttled up, but that's just a SWAG. As for 'going to run 8', depending on the variables above, you might never go to run 8, or you might push the brake handles to release and pull it right out to 8 and let 'er go.

Given all of the above...

I live in the Missouri River Valley, on the historic CB&Q from North Kansas City to Lincoln. It's now part of BNSF. Where I live, we have several extended (up to 4 miles long) passing sidings (I suspect someday they'll be linked together for doubletrack). It's flat in the river basin. I've seen inbound coal loads, typically with 1-2 SD-70s (or GE equivalent) on point and 1 SD-70 on distributed power take a train from dead stop to 50MPH inside of five miles.

John_Perkowski wrote:Given all of the above...

I live in the Missouri River Valley, on the historic CB&Q from North Kansas City to Lincoln. It's now part of BNSF. Where I live, we have several extended (up to 4 miles long) passing sidings (I suspect someday they'll be linked together for doubletrack). It's flat in the river basin. I've seen inbound coal loads, typically with 1-2 SD-70s (or GE equivalent) on point and 1 SD-70 on distributed power take a train from dead stop to 50MPH inside of five miles.

Thanks, John. Wow - 5 miles. Makes sense. It's not exactly like starting a car from a dead stop!
The coal trains here have four EMD or GE 44s - two pulling and two pushing 120+ cars of coal at around 140 tons each. They could run with two or maybe three units, but when they are southbound near Colorado Springs they need a little help because of the Palmer Divide.

On another note, I miss the coal trains on Tennessee Pass back in the '90s. Sometimes NINE AC4400s in full throttle. I think the grade is 3.5%.

Say the train has 120 cars, each 143 tons total. Two units, each 210 tons, and we'll assume they can each do 3700 rail horsepower at any speed, but can't exceed 150000 lb tractive effort. We'll assume the train's rolling resistance at speed V (in miles/hour) is 36000 pounds, plus 800 times V, plus 6.2 times V squared-- good a guess as any.

On level track the train will eventually reach 37 mph-- after the first mile it's doing 23 mph, after three miles 30 mph, after five miles 33 mph. On a long 0.3% downgrade the train will be doing 50 mph five miles from the start-- on 0.3% down the train would eventually reach 59 mph just coasting, with no power from the engines.

I appreciate your response, timz. Interesting stuff!

One point that was not mentioned was that throttling up has to be done with care. The locomotives can produce enormous amounts of tractive effort at low speed. This diminishes as speed increases. Too much power too fast will rip apart a train. The pushers can produce too much buff force. This could jackknife the cars immediately ahead. The locomotive load needs to be watched carefully.

The acceleration has to do with the horsepower available. I run lots of unit trains. The more engines, the quicker I accelerate.. I can also maintain higher speeds on hills.

As others said, the topography of the land, and operating factors play in. Sometimes curves take careful handling. Too much power may make cars stringline. This is when they jump the inside (low) rail, and go in the direction of a cord, between two points, in a straight line.