Western Railroad Discussion > What's a Fouling Point?

Went railfanning along a BNSF line and saw a target with the letters FP in black on a yellow background. I know the letters stand for Fouling Point but what does that mean? Thanks.

<<< Correction >>>

Oooh, how embarrasing. I had the two locations backwards, as others have pointed out below. The clearance point is where two cars would touch, and the fouling point is where the insulated joint or derail would be put, or the end of the tangent part of the siding if neither of the above is present. Other that reversing the two names, the rest of my post below is correct:

======================================================

As two tracks converge into one, there are two points of significance. One is the clearance point, which is where cars should normally be left if parked. The other is the fouling point, which is where a car on one track would physically hit a car on the adjacent track.

If you consider a siding beside a main track, the clearance point in the siding is typically where the straight track starts to turn toward the main track turnout. At this point, a car parked in the siding would have the normal clearance of several feet between it and a train passing on the main track.

The fouling point is closer to the turnout. If a car was parked right at the fouling point, and a train went past on the main track, there would be no clearance between the vertical handgrabs on the car parked in the siding, and the cars of the passing train.

FP is also where you will find the insulated joint on a block system. If you leave a car past the FP, it knocks down the track circuit.

Nudge

On the Southern Pacific in non-CTC territory, fouling point signs were placed at the locations "run8" calls "clearance points," that is, the point in the siding where the straight track starts to turn toward the main track switch. Originally, the signs were wood with "Fouling Point" spelled out. In 1956, the design was changed to steel posts and small metal plates that had initials "F.P." on them.

In CTC territory, in the 1940s the SP started using wooden "Fouling Point 500 FT" and "Fouling Point 1000 FT" signs placed in advance of absolute signals. Such signs were sometimes placed along sidings in regular ABS territory also. The 1956 sign revision saw these signs changed to metal with plates reading "F.P. 500" and "F.P. 1000."

The BNSF in the San Joaquin Valley uses FP 500 and FP 1000 signs on its CTC sidings I recently noticed.

"Clearance Points" are defined as thirteen (13) feet between track centers, at least as defined in the Republic of CA.

"Foul Points" are defined by the insulated joints.