It doesn't seem like the lead-up data to the derailment yields much information (although it reminds me of Minard's "Napoleon's March" graphic without all the valuable info). Train 188 pretty much stayed near the median speed of trains at every marked point - until it didn't. If the train was speeding at along the length of the journey then the accident would seem, well, less accidental. But as it is, if the operator really just lost a sense of where they were on the route it seems to me that's a lousy safeguard for proper speed control to have the operator "know" the course. We don't do that with automobile drivers; that's why we have speed limit signs.

I don't have anything to add other than that I am a regular reader of your blog and love it. Keep up the great work.

I think the way that I would really like to see this is with the first map, as is, aligned with a two charts, above or below, that map the speeds.

One, a standard line chart, with the median speed as one line, and train 188 as another. The x axis aligning roughly with the spatial layout of the route.

The other, a variance from median chart.

I think having the visual of the route is great, but I don't think the bands and lines give any good understanding of the speeds at all.

Something like this (very very very rough) mock-up:
https://i.imgur.com/BznSBC0.png

Is median the best statistic to use here? It tells us that the train entered the bend faster than average, but not that it necessarily entered too quickly. Did other trains over the 3 days enter the bend at the same speed? Maybe that driver often approaches the bend at that speed and that's accounted for in the median by another driver always entering the bend extremely slowly.

It does show that before the bend, the train was travelling at the same speed as the average train and has gone in to the bend faster than you would expect based on its journey until that time.

To be honest I think these are awful. I would suggest a small multiples approach. I think the map is good, but I might do one map coloured by speed for the typical train and put another one for the accident train next to it.

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

(Name is required. Email address will not be displayed with the comment.)

## NEW BOOTCAMP

See our curriculum, instructors. Apply.
Marketing analytics and data visualization expert. Author and Speaker. Currently at Columbia. See my full bio.

## Book Blog

Graphics design by Amanda Lee