Remain alert for conditions that can cause slack action (e.g. train brake, change in grade or change in speed).

Remain alert for conditions that can cause abrupt changes in speed, e.g., train braking, changes in grade, wet or icy tracks, and entering or leaving a rail yard or train station.

What does "grade" and "slack" mean in these sentences? It seems that none of the definitions found in a dictionary fits in this context. Does "grade" also mean gear (gear shift)?

  • If you ever post a quote, please remember to state the source, and link to it if possible. In this case this looks like technical writing for operating a locomotive.
    – James K
    Commented Apr 7, 2019 at 8:42

1 Answer 1


These terms are North American railway ("railroad") related.

Slack action is what happens to the cars of a train when it changes speed suddenly. The cars are not rigidly coupled. If the train slows down, each car can try to run into the one in front; if it speeds up, each car will try to pull back. Both these actions place a strain on the couplings between the cars, and, especially with a long heavy train, if not controlled, can cause the train to break apart.

In railroading, slack action is the amount of free movement of one car before it transmits its motion to an adjoining coupled car. This free movement results from the fact that in railroad practice cars are loosely coupled, and the coupling is often combined with a shock-absorbing device, a "draft gear," which, under stress, substantially increases the free movement as the train is started or stopped. Loose coupling is necessary to enable the train to bend around curves and is an aid in starting heavy trains, since the application of the locomotive power to the train operates on each car in the train successively, and the power is thus utilized to start only one car at a time.

Slack action

The grade of a section of land, road, railway is its slope, inclination or gradient:

The grade (also called slope, incline, gradient, mainfall, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal.


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