Edited 29 Sep 2014 08:00, 6 years ago, edited by historian

Has no one actually read the preliminary report?

The preliminary report clearly fingers a lack of stiffness in the broad gauge point blade. This *is* a design problem, but not one directly related to the XPT flange width. I quote from page 7:

Examination of the lead wheelset/lead bogie of carriage XAM2176 (wheelset with narrowest field edge to flange face distance) confirmed that there was limited rim contact on the rail head through the transfer area. With the left wheel of XAM2176 running on the right edge of the broad gauge switch rail (in the direction of train travel), this would likely have applied high outward torsional loading on the switch blade. In circumstances where the broad gauge switch blade is insufficiently restrained through the transfer area, the switch blade can both roll and flex outward, increasing the likelihood of one or more wheels dropping in between the track and causing the train to derail.

The report states that the design gauge at this point was 1480 mm (the actual gauge was 1486, but the reports suggest that this was caused by the switch blade being permanently bent by the derailment). The maximum gap that could be spanned by the worst XPT wheelset should have been 1503 mm (= 127 mm rim width + 1357 mm back to back wheel + 19 mm minimum flange width). This means that there should have been 23 mm of tread still on the left hand rail.

The narrow width of the XPT treads made it more likely to derail (a 140 mm wheel rim would have 36 mm still on the rail), and increases the eccentricity of the loading on the switch rail. And the risk would be increased with flanges near the condemning width, and narrow back to back measurements.

And, yes, a dual gauge turnout is a complex engineering design. Particularly where you are trying to build a dual gauge turnout with relatively little difference in the two gauges out of relatively heavy rail.

Edited 29 Sep 2014 00:05, 6 years ago, edited by historian

Has no one actually read the preliminary report?

The preliminary report clearly fingers a lack of stiffness in the broad gauge point blade. This *is* a design problem, but not one directly related to the XPT flange width. I quote from page 7:

Examination of the lead wheelset/lead bogie of carriage XAM2176 (wheelset with narrowest field edge to flange face distance) confirmed that there was limited rim contact on the rail head through the transfer area. With the left wheel of XAM2176 running on the right edge of the broad gauge switch rail (in the direction of train travel), this would likely have applied high outward torsional loading on the switch blade. In circumstances where the broad gauge switch blade is insufficiently restrained through the transfer area, the switch blade can both roll and flex outward, increasing the likelihood of one or more wheels dropping in between the track and causing the train to derail.

The report states that the design gauge at this point was 1480 mm (the actual gauge was 1486, but the reports suggest that this was caused by the switch blade being permanently bent by the derailment). The maximum gap that could be spanned by the worst XPT wheelset should have been 1503 mm (= 127 mm rim width + 1357 mm back to back wheel + 19 mm minimum flange width). This means that there should have been 23 mm of tread still on the left hand rail.

The narrow width of the XPT treads made it more likely to derail (a 140 mm wheel rim would have 36 mm still on the rail). And the risk would be increased with flanges near the condemning width, and narrow back to back measurements.

And, yes, a dual gauge turnout is a complex engineering design. Particularly where you are trying to build a dual gauge turnout with relatively little difference in the two gauges out of relatively heavy rail.

Edited 29 Sep 2014 00:02, 6 years ago, edited by historian

Has no one actually read the preliminary report?

The preliminary report clearly fingers a lack of stiffness in the common point blade. This *is* a design problem, but not one directly related to the XPT flange width. I quote from page 7:

Examination of the lead wheelset/lead bogie of carriage XAM2176 (wheelset with narrowest field edge to flange face distance) confirmed that there was limited rim contact on the rail head through the transfer area. With the left wheel of XAM2176 running on the right edge of the broad gauge switch rail (in the direction of train travel), this would likely have applied high outward torsional loading on the switch blade. In circumstances where the broad gauge switch blade is insufficiently restrained through the transfer area, the switch blade can both roll and flex outward, increasing the likelihood of one or more wheels dropping in between the track and causing the train to derail.

That is, the XPT was diverging to the left at the turnout. The right hand wheel of the wheelset was hard up against the right hand (common) switch blade providing the force to turn the carriage around the curve. The report is suggesting that this force caused the switch blade to distort, widening the gauge further and causing the wheelset to fall between the rails.

The report states that the design gauge at this point was 1480 mm (the actual gauge was 1486, but the reports suggest that this was caused by the switch blade being permanently bent by the derailment). The maximum gap that could be spanned by the worst XPT wheelset should have been 1503 mm (= 127 mm rim width + 1357 mm back to back wheel + 19 mm minimum flange width). This means that there should have been 23 mm of tread still on the left hand rail.

The narrow width of the XPT treads made it more likely to derail (a 140 mm wheel rim would have 36 mm still on the rail). And the risk would be increased with flanges near the condemning width, and narrow back to back measurements.

And, yes, a dual gauge turnout is a complex engineering design. Particularly where you are trying to build a dual gauge turnout with relatively little difference in the two gauges out of relatively heavy rail.