Broken lag bolts caused UP oil train derailment in Mosier, OR

This is a photo of a graphic UP presented at a town meeting from KGW

The headline and UP talk about "a broken lag bolt." But it turns out UP has to allow several of them in a row to break before the rail will move enough to cause a derailment.

(Be warned, that KGW link hogged a lot of CPU, memory and Ethernet bandwidth.)

"As the trains move around the curve, they apply a lateral force to that rail, shoving that rail out. What holds that rail intact are those lags," said a Union Pacific spokesperson. "If all those lags are broke for so many ties in a row, it allows that rail to spread out, which allowed the wheel to fall in. We had one wheel down at the point of derailment."

Union Pacific officials said the lag bolt would have been detected by a gauge restraint measurement system but that test is only done once every 18 months. That test will now be done four times a year, officials said. 

(UP via KGW)

It sounds like UP should use either bigger bolts, better steel, or both. And they need a test that detects a single broken bolt, not wait until a bunch of them have broke and the track can move. It makes you appreciate how will track spikes and tie plates have worked for over a century.