Tyabb level crossing crash figures don’t add up

Facts and figures about the Tyabb level crossing crash have been reported in the Herald Sun and Seven/Yahoo News.




The diagram below shows a google image used to illustrate some of the figures.  This image has a scale which indicated that the station is about 200m from the crossing at “X” where the collision occurred.  This measurement has been used to place the approximate yellow lines at100m spacing on the image.

The report says the following.

The car was moving at 15-39km/hr at “X” and braked less than 2s prior (how much less than 2s?).

Train emergency brake was on at 11m before the intersection (labelled here as “X).

Train driver could see car at -100m (labelled here as “A”).

Do these figures make sense?

The red line on the graph is intended to show the speed of the train from 100% to 0% at the platform starting to brake just before the intersection “X”.

The blue line shows the same deceleration if the driver sees a problem ahead when at “A” and brakes a little after (allowing say 1s for reaction).

If the car was at “B” when the train was at “A” how did they collide?

The train speed is not listed but it does not seem likely that a car visible when the train is at “A” would still be at the intersection when the train arrived.

For the sake of example, if the train was moving at, say, 15m/s (54km/hr) at “A” and braked at -11m and stopped at +200m, the time from “A” to the intersection “X” would be (the red line):

t(red line)=89/15 + 11/15/0.97 = 6.7s.

t(blue line)=15/15 + 85/15/0.80 = 8.1s.

A vehicle at “B” (for the sake of example, lets say that is 15m from the intersection) travelling at ~ 10m/s (36km/hr) would move 67m (if the train braked just before the intersection, red line) or 81m (if it braked earlier, blue line) and therefore would either way be well clear of the intersection by the time the train arrived (i.e. somewhere near “C).

The reports therefore do not seem to add up.

About John Culvenor

Hi, Thank you for taking a look at this blog. I work in engineering, ergonomics, creativity, design, training, etc. Often this is about helping solve legal puzzles through accident analysis. Sometimes it is about thinking up better designs for equipment, workplaces, and systems. This blog is about good design and bad design, accident analysis and how it can be done better, and how we can make a better, safer world by design!
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