Speedometer Reading After Crash

[panabiker]

Over the weekend, I had a conversation with some friends on a recent
accident involving NJ governor. It was reported by news media that the
SUV was going at 91 MPH prior to the crash. My question was how they
found out the speed, and one answer was that a speedometer would stuck
at the speed the moment of the impact. I find it very hard to believe
that any speedometer would stuck at the correct reading considering
the violent nature of the collisions, unless the speedometers are very
specially designed to record speeds and to sense the crash. Can anyone
shed some lights on how accident investigators figure out the crash
speeds?

[Kevin Bottorff]

panabiker <ghu...@comcast.net> wrote in news:1177600190.710477.26660
@u32g2000prd.googlegroups.com:

the black box will record the last 5 seconds of info on newer vehicles.
KB

--
Thunder Snake #9
"Protect" your rights or "lose" them.

[Ray]

onboard black box.
confession.
measuring skid marks.
recreating the accident scene - how far did the vehicle slide, etc...

but, probably just an educated guess.

Ray

[N8N]

Probably read it off the "black box" instead of looking at the
speedometer.

nate

[mr_mushroom]

it was likely the black box.
in the old school, they would formula it out.
weight of vehicle, length of skid marks, impact damage, etc.
although
unless there's a full on proper investigation, they're wrong.
my girlfriend was in a crash once, the cops said they hit that fence at
80 MPH.
hmmmmm...
1982 K10 @ 80mph + fence
seems like they should have done more than just knock the fence over
from 80 miles per hour. i don't care what anyone says, 80 is fast,
technically speaking, and that truck is very heavy. also considering
that not wearing a seatbelt in a 30mph crash has been known to cause
death. oh and plus no one was wearing seatbelts.
so sometimes they just throw numbers around, i think they think they're
cooler when they do that shit.

--
mr_mushroom
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[Steve W.]

Easy to do IF you have access to the proper software. They just plug
into the OBD port and query the airbag module for the vehicle parameters
at the time it deployed. It saves the information just like the freeze
frame data that gets stored when the MIL comes on. It will tell them the
speed, throttle position, engine RPMs, in what order the sensors for the
bag(s)tripped,if you had the brakes applied (also shows if ABS was
functioning at the time), seat belt use, exterior temperature. Plus a
few other items.

--
Steve W.

[maxwedge]

No belt and 90 mph, I'd like to get a ticket for either in Jersey and
have my say in court. Tricky as to what agencys have access to the
SIRS module info after a deployment. Good info., lugnut.

--
maxwedge
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[Ad absurdum per aspera]

> No belt and 90 mph, I'd like to get a ticket for either in Jersey and

> have my say in court. Tricky as to what agencies have access to the

> SIRS module info after a deployment.

Hopefully as a mere matter of getting a ticket -- actually stuff the
car at 90 with no belt, "you should have such problems."

To get back to the original poster's question: I doubt that they
would find a speedo stuck at 90 (in the car, that is; if your
Speedo gets stuck at 90; well, you and all your buddies at the
senior center should have such problems). Needles getting frozen at
some reading is an ancient theme from fictional and apparently some
factual accounts of aircraft crashes, violent disruptions of one's
person in the era of mechanical wrist watches, etc. I am thinking
that that takes extreme g's, especially in the case of an instrument
where the position of the needle is a dynamic rather than a static
affair (stopping a mechanical clock might be a lot easier to arrange,
John Cameron Swayze notwithstanding).

A quick glance through the literature of a field not my own indicates
that a slap mark on the *face* of a speedometer is what investigators
are usually looking for after a motor vehicle crash, not the needle's
actually being frozen. Mythbusters could doubtless have a lot of
fun with some old jalopies and an abandoned runway in this regard.

As others have pointed out, there are several other ways of
determining the crash speed through forensics at the general crime
scene, perhaps onboard computers, and occupants coming clean about the
situation.

Cheers,
--Joe

[Al]

keep in mind - it was a state police owned and operated vehicle, and the
occupant was the governor of the state - I would assume that both the
vehicle and the governor are tracked by GPS most of the time.

[ROY BRAGG]

Software is not necedssarily needed, speedometer needles have stuck at speed
in accidents many years before onboard computers were installed on cars.
Roy
"Steve W." <ya...@yahoo.com> wrote in message news:f0qse2$p3l$1...@aioe.org...

[IRON...@gmail.com]

WHEN ON IMPACT THE NEEDLE SLAPS THE GAUGE AND LEAVES A A MARK ON IT
THE SAME COLOR AS THE POINTER

[Accident Investigator]

The comments above have been interesting to read. We, however, need to remember that modern vehicles no longer have speedometers that work by attaching a cable to a vehicle wheel and the amount of revolutions that a wheel turns is transfer to the speedometer that works with internal weights that measure how far the separate the higher the revs.
Modern speedometers are electronic that receive a signal from a sensor on the vehicles gearbox and the analog needle moves to the speed that the vehicle is moving. There are small electromagnets in a servo that move the needle around. If the power to the vehicle is shut off due to a violent crash there is no residual power left to return the needle to its resting place. That is why the speedometer can give a good indication of what the vehicles speed on impact was. This method is accepted by Police in USA, Canada, UK and Australia. I hope this explains why this method is used. Black boxes are not fitted in all vehicles in other countries.

[thor...@hotmail.com]

i mostly agree with the above but will point out " no longer have speedometers that work by attaching a cable to a vehicle wheel " // was only true for bicycles and motorcycles. Car speedometers have always read thru a cable that attaches to the transmission, the modern difference is the magnets and sensors, the originals were simply spun by a gear in the transmission.

[Steve W.]

Not always, VWs and some other imports used a cable to a front wheel for
the speedo drive. So did cars that used multi-speed rear axles as did
many early cars.

--
Steve W.