S = L-cV
Where-
S = Load severity, defined as the lateral load applied to the fastener system (kips).
L = Actual lateral load applied (kips).
c = Coefficient of friction between rail/tie, which is assigned a nominal value of 0.4.
V = Actual vertical load applied (kips), or static vertical wheel load if vertical load is not measured.
Where-
UTG = Unloaded track gage measured by the GRMS vehicle at a point no less than 10 feet from any lateral or vertical load application.
LTG = Loaded track gage measured by the GRMS vehicle at a point no more than 12 inches from the lateral load application.
L = Actual lateral load applied (kips).
V = Actual vertical load applied (kips), or static vertical wheel load if vertical load is not measured.
GWP = Gage Widening Projection, which means the measured gage widening, which is the difference between loaded and unloaded gage, at the applied loads, projected to reference loads of 16 kips of lateral force and 33 kips of vertical force.
49 C.F.R. §213.333