What is the biggest screw ups you seen while working on the railroad?

More than once.

One April night, while working as a utility man, I doubled a road train, right over a derail and put one truck of a 300-foot well car on the ground. I retook my conductor test the next day and was promoted to conductor.

These are more funny screw ups than serious ones.

I had a trainmaster meet us at the YD (YD is our term for our main building where we get the paperwork and such), he told us he was going to ride with us instead of driving to our destination. Apparently he wanted to go to Chicago but we were heading West. He went into the second unit and I guess he fell asleep. We woke him up when we got in and well...you can guess what happened. 400 miles away and he HAD to be there in the morning, it was 2am when we got in not to mention it was winter and we had a snow storm. No other train was leaving anytime soon so he drove the 400 miles to Chicago.

Trains were stacked up on one of our lines going to Chicago. The train ahead of us had to go on a foreign line. Our dispatcher told that train to come on down and watch for the foreign lines signal. They came down to look but it was all red. Their dispatcher came on and said that they could no longer take the train that it had to wait. Everything was blocked and we couldn't move traffic. Our dispatcher was pissed when he found out the other dispatcher basically lied. He called their dispatcher on the phone but he forget he had the radio keyed and he laid into their dispatcher.. We got to hear the whole conversation...and it was not even PG-13. It made for some nice entertainment for all of us.

EDIT: Here's another one. We had a student conductor with us on a run into Chicago. Everything when good and had a quick run. We got into the hotel around 6am and the crew had breakfast together. After that I went back to my hotel room and went to sleep. Got called on our rest and later during our trip back we found out he checked out of his room at 11am because that was the checkout time on the door. Apparently he slept in the lobby. I don't know what he was thinking when he checked out. He wasn't a young guy, he was in his 40s.

The other two big screwups are BNSF giving priority to Amtrak on our territory. There's numerous times on a trip were we will sit at a red signal for hours waiting for Amtrak to get around us. A six or eight hour run will turn into a ten or twelve.

The biggest screw up in the history of the railroad industry will have to be Southern Pacific selling itself to the DRGW.

well to me it would that Metrolink crash in southern California the engineer was texting crash head onto another train know as the Northridge incident