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This is where I found it.

x*x / 20 + x = Overall stopping distance in feet

x=speed

So say you're going...30..

30*30/20+30=75 ft.

Someone let me know if I am wrong.

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A vehicle traveling 50 miles per hours is traveling 73.5 feet per second (1.47 X M.P.H.)

Perception time is 1.5 seconds

We multiply 73.5 X 1.5 = 110 feet

D=S²/(30*f)

D=50²/(30*.75)

D=111 feet

Total Distance is 110 feet + 111 ft = 221 Feet

Remember f is the drag factor. I used .75 for average travelled dry pavement, that can change dramatically based on the drag factor. You have to either do test skids or use a drag sled. Also you should computer for m=grade and super-elevation to get an accurate number.

Hope this helps, recon class!!

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:stupid: my brain hurts too much math ...hehe

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Speed in miles-per-hour must be changed to velocity in feet-per-second. This is done by multiplying speed by 1.466 (a constant...divide velocity to get speed) thus:

s(1.466)=v..............or...........speed (in miles-per-hour) multiplied by 1.466 will give you the velocity in feet per second. conversely, velocity (in feet-per-second) divided by 1.466 will give you speed in miles-per hour.

1.5 seconds is an AVERAGE perception/reaction time. This is the time it takes a person to perceive the threat and react to it, i.e., see the vehicle, understand the threat and actually apply the brakes.

If you multiply the velocity by 1.5 seconds, it will give you a distance in feet:

X f/s (1.5 s) = Y feet. ( the units of time cancel out leaving only the unit of distance).

It has been my experience using a calibrated drag sled that the deceleration factor (f) is nearer to 0.80-0.88 in real life (dry pavement, not traffic polished or new). You need to factor in the grade and superelevation (crown) of the surface...easy to do if you pull your drag sled in the direction of the skid: those two variables are then factored in 'automatically'.

Keep in mind that 1.5 seconds for the perception/reaction time is an average and differs from individual based on age, driving ability and overall health.

Now, feel free to contact the troop duty officer in your area to get the assistance of your friendly neighborhood reconstruction specialist, at no cost to you or your department!

Just thought I'd share that...

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Anyway, the science is called biokinetics, and I don't possess sufficient knowledge (for now!) to address the subject at length (or ad-nauseum for some ).

I am, however, ready, willing and able to bore you to death with lengthy-geeky discussions about most reconstruction topics! :shock:

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Actually you'd be surprised how FEW accident reconstruction certified entities are in the commonwealth. Right J809!?RPD931 @ 13 Sep 2004 13:50 said:Yeah I noticed that many of the troopers know reconstruction stuff as good as I tie my shoes. It's like basic math for them.

:wink:

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