part II of john mcphees New Yorker article on Powder River run, at long last

Very good story.

He missed a decimal point, though - three 4400 HP diesel locomotives equal 13 thousand, not 13 hundred, horsepower.

And the comparison of AC vs. DC locomotives was not all that well made. Saying that it takes fewer 4500 HP AC locomotives than 1500 HP DC locomotives isn't exactly a startling revelation and doesn't make a case for AC.

Speaking of AC, are the engineers given any better go control than the 8 discrete steps of the DC locos? Surely after 100 years, something better than the old trolley stepper controllers can be had.

AC locomotives tend to have better traction control and a higher tractive effort for a given horsepower. Thus, they can haul heavier loads. Of course, hauling a heavier load with the same horsepower means running at lower speeds.

Greg Gritton

Tractive effort is the amount of the driving power available that can be transferred to a horizontal pulling/pushing power. This is to a very high degee a function of the weight on the drive wheels times the coefficient of friction. AC doesn't have anything to do with this.

As I understand/surmise, AC locomotives are AC only in the generating side and are pulsed DC on the drive side. This leaves open the possibility of measuring the drive motor speed between pulses and compensating for any detected slippage. Thus, the AC locomotives can automagically better apply the available power to driving force up to the tractive effort limit.

Eight throttle steps are still provided. They don't really need any more than that.