# Calculate Motive Power Needed

## Simple calculations to determine the number of locomotives needed to power a train.

**Basic Calculations:**

Tractive Effort: | (Horsepower x 308)Miles Per Hour |

Tonnage Rating: | Tractive Effort total from above(2000 x % of grade) ^{1} |

Locomotive Total: | Train tonnageTonnage Rating from above |

**Sample Calculation:**

So, here's a calculation based upon my planned model of Cajon Pass. The ruling grade is 2.2%. Motive power will be 4400hp GE Dash 9's, pulling a train weight of 7000 tons.

Tractive Effort: | (4400 x 308)25mph |
= 54208 |

Tonnage Rating: | 54208(2000 x 2.2) |
= 12.32 (1232 tons)^{1} |

Locomotive Total: | 70001232 |
= 5.681, rounded up, 6 Dash 9's needed ^{2} |

**Notes:**^{1}Use first 4 number w/o decimal point, i.e. 12.32 = 1232.^{2}Rounding up to the the next even number works fine. However the .681 can be made up with a locomotive that provides ~75% of the power of the Dash 9, ~3300hp.