Freight Train Motive Power

Gpritch posted:

I have a general railroading question - 

Most of the freight trains I see have multiple locomotives.  Is this generally to increase the overall horsepower

Absolutely YES!

or is it more so due to an inherent lack of reliability in the locomotive itself, think as a live spare?

No. The reliability/availability of todays modern locomotives is VERY, VERY high. Railroads monitor what is known as MTBUS, i.e Mean Time Between Unscheduled Shoppings. 

  Any insight on this would be appreciated.

Hot Water posted:

Gpritch posted:

I have a general railroading question - 

Most of the freight trains I see have multiple locomotives.  Is this generally to increase the overall horsepower

Absolutely YES!

or is it more so due to an inherent lack of reliability in the locomotive itself, think as a live spare?

No. The reliability/availability of todays modern locomotives is VERY, VERY high. Railroads monitor what is known as MTBUS, i.e Mean Time Between Unscheduled Shoppings. 

  Any insight on this would be appreciated.

 

Hot Water, my experience in Quality Improvement exposed me to various opportunities to adopt MTBF (mean time between failures) as a quality metric. Is the railroads’ use of MTBUS a specific MTBF metric? 

That is to say, are there other railroad processes that use different named MTBF metrics?

TM Terry posted:

Hot Water posted:

Gpritch posted:

I have a general railroading question - 

Most of the freight trains I see have multiple locomotives.  Is this generally to increase the overall horsepower

Absolutely YES!

or is it more so due to an inherent lack of reliability in the locomotive itself, think as a live spare?

No. The reliability/availability of todays modern locomotives is VERY, VERY high. Railroads monitor what is known as MTBUS, i.e Mean Time Between Unscheduled Shoppings. 

  Any insight on this would be appreciated.

 

Hot Water, my experience in Quality Improvement exposed me to various opportunities to adopt MTBF (mean time between failures) as a quality metric. Is the railroads’ use of MTBUS a specific MTBF metric? 

That is to say, are there other railroad processes that use different named MTBF metrics?

Well, mean time between failures (MTBF) is not quit as important to a railroad Mechanical Department, since if such a "failure" does not effect train performance (no train delay involved), and such a "failure" can be corrected during the next SCHEDULED shopping, then such a failure is not near as importantent as a failure that requires the unit to be shopped/repaired outside of its SCHEDULED SHOPPING. Thus, MTBUS is VERY important to today's modern locomotives, which only require to be shopped every 92 or 180 days for scheduled inspection, per FRA regulations.  

To further explore this though isn't it more about total tractive effort than raw horsepower?  I know HP is important, but my understanding is that the RR's discovered during the 1990's HP race that it wasn't the ace everyone thought.  Hence why the remaining AC6000's, SD80's, and SD90's have been rebuilt as approximately 4300-4400 HP units.

It would make sense to me tractive effort is what gets a train moving and helps up up hill etc  (like torque) and HP is more or less what keeps them at speed.

Would it be safe to assume on a flat and level grade that once started you could actually shut units down once moving at speed?  I know this probably isn't practical or efficient, just asking a theoretical question.

I may be completely off base or wrong in my post here, just further opening this discussion up as it is very interesting.

TexasSP posted:

To further explore this though isn't it more about total tractive effort than raw horsepower? 

Tractive effort is starting/hauling tonnage. Horsepower is what accelerates that tonnage.

I know HP is important, but my understanding is that the RR's discovered during the 1990's HP race that it wasn't the ace everyone thought.

Not really. High HP is important, especially for inter-model freight, that is time sensitive, and thus high train speed (70 MPH) is important over long distances.

  Hence why the remaining AC6000's, SD80's, and SD90's have been rebuilt as approximately 4300-4400 HP units.

Sort of, yes, however the Conrail SD80MAC units, at 5000 HP were deemed quite successful and NS still uses them, to my knowledge. The 6000 HP units were NOT reliable and wound up being just too much HP in a single unit, plus they were VERY heavy.

It would make sense to me tractive effort is what gets a train moving and helps up up hill etc  (like torque) and HP is more or less what keeps them at speed.

Correct.

Would it be safe to assume on a flat and level grade that once started you could actually shut units down once moving at speed?  I know this probably isn't practical or efficient, just asking a theoretical question.

What you describe can, and is, accomplished with todays modern computer controlled high HP units.

I may be completely off base or wrong in my post here, just further opening this discussion up as it is very interesting.

You done good!

Al Krugs' website used to have lots of info about tractive effort vs. hp esp. when slugging up steep hills with a bunch of SD40-2's pulling coal trains. Wonder if he ever put all that info back online?

Casey Jones2 posted:

Al Krugs' website used to have lots of info about tractive effort vs. hp esp. when slugging up steep hills with a bunch of SD40-2's pulling coal trains. Wonder if he ever put all that info back online?

Have Google search for Tales From the Krug. Al has LOTS of information & photos on his site.

When SP was buying lots of GP40-2 and 60 locomotives, many had "Select a Power" or something like that.  Engineer could adjust each MUed locomotive to provide power or go into neutral.  I think SP got it to save costs on fuel.

Is this still on the market today?

Corrections welcomed!

Back in the PennCentral days 6-7or 8 loco's was the norm...the reason was so that maybe 3 would make it back due to deferred maintenance  ....not so today ,mostly multi loco's are for horse power ..... 

Dominic Mazoch posted:

When SP was buying lots of GP40-2 and 60 locomotives, many had "Select a Power" or something like that.  Engineer could adjust each MUed locomotive to provide power or go into neutral.  I think SP got it to save costs on fuel.

Is this still on the market today?

I don't know if they still sell the manually-operated Select-A-Power, but it's built right into BNSF's huge fleet of 4300 HP road locomotives.  That and more.  The theory back in the 1980's was that diesel engines are most efficient when heavily loaded at their maximum rated RPM, so Select-A-Power was used to isolate a unit leaving three running in Run-8 instead of four running in Run-5.

Nowadays, trailing units automatically reduce and increase power to keep speed steady in whatever throttle position is most fuel efficient for the desired result.

You can't tell it from trackside, as locomotive manufacturers stopped building in a definite RPM change for each throttle position 20 years ago.

If manual Select-A-Power is still available, the customers would be regional railroads which use locomotives such as SD40 variants.

Hot Water posted:

TexasSP posted:

To further explore this though isn't it more about total tractive effort than raw horsepower? 

Tractive effort is starting/hauling tonnage. Horsepower is what accelerates that tonnage.

 

 

This is Newton's Second Law of Motion in action. Force (F) equals (=) mass (m) multiplied (x) by acceleration (a). Or F = ma. Divide both sides of the equation by mass results in: acceleration equals force divided by mass. 

Quite clearly states:

In the form a = F/m we can easily see that the acceleration of the body is directly proportional to the resultant force acting on it. Tractive effort, which is measured in units of a force (pounds or Newtons), accelerates the train; that is the resultant force applied to the mass of the train.

Horsepower is the ability to do work; the constant in the horsepower equation is a work function and has the units of work. The more horsepower the more work that can be done.  

No argument with Newton.  However, the same tractive effort in four 2300-horsepower engines vs the same tractive effort in four 3600-horsepower engines will not make a difference in being able to start and pull the same train.  The higher horsepower locomotive of the same tractive effort will achieve maximum authorized speed on level track in less time than the lower horsepower engine.  The higher horsepower locomotive will be able to maintain a significantly higher speed on ascending grades.

That's why midwestern drag freights are assigned 1.5 horsepower/ton, expedited trains get 3.5 horsepower/ton, premium service trains get 4.5 to 5.0 horsepower/ton, and passenger trains get above 6 horsepower/ton.

Hot Water posted:

Casey Jones2 posted:

Al Krugs' website used to have lots of info about tractive effort vs. hp esp. when slugging up steep hills with a bunch of SD40-2's pulling coal trains. Wonder if he ever put all that info back online?

Have Google search for Tales From the Krug. Al has LOTS of information & photos on his site.

I found his page...archived via Wayback Machine. Very informative reading.

TE vs HP