Related to this, you will notice a bit of a thump as a train passes between a forgiving roadbed, like ballast, and a solid roadbed, like a bridge. It's more noticeable as a passenger.

Boomer Wrote:My friend Blake and I were at the remnants of Greenville Yard near Jersey City, NJ many years ago. There was still a car float operation. We watched as a GP pulled and pushed cars through some track where the rails lifted off the ties (apparently no spikes) and bowed to almost touch the sill of the boxcars doors.
Mark

Yikes -- I wonder how common that is ! Rob

The trackage goes up and down considerably in some places. It's a normal occurance and with daily use it may cause spikes to start coming dislodged or 'lifting'.
It doesn't help that some ties/ trackwork look like this...and this is on the Toronto to London mainline right behind my house at the end of my garden.

One good tie every 8 feet is good enough for class 1 track which is 10 mph freight and 15 mph passenger.
Check this page out for the description of a good tie....
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Charlie

Somewhere I have some video of the diamond at Marion, OH, flexing up and down a good 6" as an NS coal train rolls over it. It was quite surprising, and quite noticeable. This was a diamond of 2 main line class 1 tracks.

Squid, possibly the worst track in the business is the diamond. I was in charge of making repairs to a diamond on a small switching service railroad. The ties have to be placed diagonally and need be extremely long to boot, nothing like the ties on an atlas diamond. Joint bars are a complete disaster and a nightmare to tighten and to keep tight, and you are right, they pump badly too, very hard to tamp with a machine so jitterbugs are best, but no room to get the stone under the ties, and almost too heavy to jack up. It is not hard to see why they are avoided when possible.
Charlie

I have watched many trains. on main lines, sidings, yards & customer owned tracks. I have seen this every where and never thought much about it. I assumed it was just the way it is. As mentioned before movement is engineered into everything. That keeps it from breaking under stress. Have you ever stood on a busy highway bridge? It can be frightening.

What is serious is when there is mud under the roadbed and the pumping starts covering (or replacing) the ballast with mud. That gets the track crews out fast.
There was a double slip or two at Toronto Union that always seemed to have mud over the ties.