49 CFR §299.335

1. (a)Derails shall be installed at locations where maintenance-of-way equipment can access track other than Class H0, in a configuration intended to derail the un-controlled equipment away from the mainline and at a distance from the point of intersection with the mainline that will not foul the dynamic envelope of the mainline.
2. (b)Each derail shall be clearly visible to railroad personnel operating rail equipment on the affected track and to railroad personnel working adjacent to the affected track. When in a locked position, a derail shall be free of any lost motion that would allow it to be operated without removal of the lock.
3. (c)Each derail shall be maintained and function as intended.
4. (d)Each derail shall be properly installed for the rail to which it is applied.
5. (e)If a track is equipped with a derail it shall be in the derailing position except as provided in the railroad's operating rules, special instructions, or changed to permit movement.