This looks like a standard length semitrailer, so call it 53 feet.
Immediately before hitting the crash bar, the semitrailer passes a fixed point on my screen in 16 frames.
The Youtube video is rendered at approximately 15 frames per second.
D = RT, so R = D/T
R = (53 feet)/(16/15ths seconds) = 49.69 feet per second, which is (“just”) 33.9 miles per hour. (Speed limit on Gregson is 25.). Still surprised it cleared the yellow light, though I guess the driver could be slowing down by the time the truck enters the frame.
(The above assumes that the playback speed of the video is equal to the true speed, which I guess we don’t really know.)
