49 C.F.R. § 213.121 : Transportation — OTHER REGULATIONS RELATING TO TRANSPORTATION — FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION — TRACK SAFETY STANDARDS — TRACK STRUCTURE — Rail joints

(a) Each rail joint, insulated joint, and compromise joint shall be of a structurally sound design and dimensions for the rail on which it is applied.
(b) If a joint bar on Classes 3 through 5 track is cracked, broken, or because of wear allows excessive vertical movement of either rail when all bolts are tight, it shall be replaced.
(c) If a joint bar is cracked or broken between the middle two bolt holes it shall be replaced.
(d) In the case of conventional jointed track, each rail shall be bolted with at least two bolts at each joint in Classes 2 through 5 track, and with at least one bolt in Class 1 track.
(e) In the case of continuous welded rail track, each rail shall be bolted with at least two bolts at each joint.
(f) Each joint bar shall be held in position by track bolts tightened to allow the joint bar to firmly support the abutting rail ends and to allow longitudinal movement of the rail in the joint to accommodate expansion and contraction due to temperature variations. When no-slip, joint-to-rail contact exists by design, the requirements of this paragraph do not apply. Those locations when over 400 feet in length, are considered to be continuous welded rail track and shall meet all the requirements for continuous welded rail track prescribed in this part.
(g) No rail shall have a bolt hole which is torch cut or burned in Classes 2 through 5 track. For Class 2 track, this paragraph (g) is applicable September 21, 1999.
(h) No joint bar shall be reconfigured by torch cutting in Classes 3 through 5 track.

49 C.F.R. §213.121