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While Mansfield (MA) is an otherwise a fairly quiet town, it is one
of the few places in the US where high-speed trains really whizz past at a
high speed!
On 2023 May 16th I (DM) went to the Mansfield MBTA station shortly
after 11am, waiting for Acela Express train #2150 to pass by, en route to
Boston. At around 11:22am the train went by at a pretty good clip. I used
the slo-mo setting (239.98 frames/second) of my iPhone 6 to take a video
of the train passing by.
The video is here.
In order to get the speed of the train from the video, I wrote a
small python code that
extracts individual frames from the video, numbers the frames, and saves
them as JPEG images. Some of the frames that show the train entering the
frame and leaving the frame are shown below.
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Notice that for each of the frames shown in the top row, the front end of the train
was almost right where the end of the train was in frame below it in the bottom row.
Given the video was take at 239.98 FPS, the time elapsed between frames 954 and 213 is
(954-213)/239.98 seconds = 3.0877 seconds.
The "overall trainset length" for an Acela Express is apparently
202,308 mm (factors like thermal expansion and contraction, stresses
and strains while in motion, etc., change the length of the train by a
few centimeters, but we'll go with the quoted length for now).
So the train covered 202, 308 mm in 3.0877 seconds. Its speed therefore
was 235.9 km/h or 146.6 mph. Not too bad!!!
Just for comparison, the speeds reported by the train to a
tracking website were
* 11:20am --- 127 mph (couple of minutes before arriving at Mansfield)
* 11:23am --- 145 mph (just after leaving Mansfield)
(According to the timestamp on my video, the train arrived in Mansfield
at 11:22:45a)
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