A train or clearance bar was installed along the inside face of a left-hand rail extending a junction to a signal protecting the junction. When a train passed over the track with the bar, the wheel flanges depressed the bar to operate a mechanical lock that prevented the lever operation of the junction.
A train bar defeated the operation of a facing point lock (FPL) lever, while a clearance bar defeated the operation of a junction lever.
A common application of these bars was in pairs at main/loop junctions. The train bar was on the main line between the main starting signal or clearance post and the junction while the clearance bar was on the loop line between the loop starting signal or clearance post and the junction.
In reality, the bars were often installed along the switch blades, and so part of the bar was required to move with the blade. A spline cannot be animated, and so this asset caanot be used along switch blades.