Here's one I have never been able to get an answer to . . .?

Question

Today our speed recorder was off -3 at 45MPH. Meaning when it indicated 45 we were actually doing 48 MPH. (perfect) :-)

What showed on the event recorder though? The actual speed or the speed that I saw in front of me? I have asked this of several road foremen and they always start with "well, I think" or "it's probably" but no one really seems to know.

Answer 1

It's a puzzler, that's for sure. I'm not sure there is any way to know for sure without downloading the data recorder and looking at the speed trace.

Both the speedo in the cab and the data recorder will take a feed from somewhere in order to ascertain the train speed. However, even if the two instruments are taking their input from the same source it does not necessarily mean that they will be reading the same speed. There could be inaccuracies in each that would mean that they are not perfectly in sync with each other across the entire speed range.

Having seen a data recorder trace, my own view is that a consistent error recorded should be indicative of an inconsistency between the data recorder and the speedo and should not result in any action being taken against the driver. However, you do get a feel for when a speedo is not entirely correct. When I get this I start to watch my point-to-point timings for any evidence to back up my hunch. If I feel adequately convinced that the speedo is wrong I will book it as a fault immediately and then drive at a speed I consider to be within the posted maximum, as I can then produce this as evidence should I be later questioned about my speed.

Answer 2

I know you're not interested in a guess, but, let's make an educated guess...

1.  Assuming the event recorder and your speedo have the same error, I would suggest you'd have engineer's being questioned constantly about their speed, the error's being present on the downloaded info.  Here I would think it a safe assumption that the event recorder is giving the true speed.

  

2.  It's all in the witness groove.  If you look on the outside of the wheel you'll see a groove running around its circumference.  The distance between the witness groove and the tread is measured to determine the actual size of the wheel.  This is done on the wheel with the alternator that supplies data either to the event recorder or the speedometer.  The reason why is to calibrate the read-out, as the wheels of the locomotive are not the same circumference, due to wear or being trued up on the wheel machine (peeler) to get rid of flat spots, for example.

All that having been said, it is logical to assume the event recorder is putting out the true speed, which is why you must watch yours.

Tell 'em that in the investigation...

Answer 3

You must have the same officers there that we have here Rango.Ours usually say ..that's a good question but i don't want to give you a wrong answer.So i'll check into that and get back to you.We actually have one here that knows something.I can hear you laughing now but it's true! He told me the conductors side is the master and the engineers side is the slave on the newer units.The recorder will read the same speed as the conductors side.On the older units it will record actual speed regardless of what yours says.Have you ever had one that reads different on both speedos and the computer screen(mainly SD 70's)?Gotta love that lol.

Answer 4

the event recorder gets the same reading off of the wheels of the engine that the gauge or compuer screen does.

Answer 5

I don't know where you are, but where I am it's only 6:12am and I can't figure out anything except the speed of drip on my coffee maker at this hour.

The speed recorded (as far as I know from speaking with a police officer who claimed I was doing 52 in a 35) It's the rate of speed detected as the vehicle passes the radar...so it would be the speed of your vehicle at that point.