Misreperesention of relative stopping distances of cars and trucks in Ny Driver's Manual

"Jack Brown" > wrote in message
...
> Apparently the New York Department of Motor Vehicles does not know
> how to graph. Look at this graph from the drivers manual below. The
> Stopping distance for a car is 193 ft but it is plotted as about 110
ft.
> Is this a stupid mistake or an attempt to scare drivers into being
> afraid of trucks?
>
> http://www.nydmv.state.ny.us/dmanual/stopdist.gif
>

I'd say either stupid mistake or mis-interpretation of the graph. Look
at the next data point (Tractor trailer with cool brakes). On the side
bar the required distance is representd as 296 ft, but on the graph is
shown as 256 ft. However, if you look at all the graphs, note that the
end of the bar is presented as a vehicle and the nose of each vehicle
appears to be at the correct point. EX: for the car, the bar appears to
end at 110 ft, but the nose of the car on the end of the bar appears to
be at about 190 ft.

Nate Nagel wrote:

> I just took a look at the graph from the original post and yes it does
> look like it was thrown together by a third grader, but also notice that
> the distances include "reaction distance recommended by the National
> Safety Council" which probably assumes a .7 second or greater RT (i.e.
> brain dead) - another common inaccuracy with such graphs.

You ought to read how they determine reaction times in the AASHTO "Green
Book." They say the average reaction time for a driver is around *2*
seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
think that it's unreasonable. Even the Bosch Automotive handbook states
that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

Nate Nagel wrote:

> I just took a look at the graph from the original post and yes it does
> look like it was thrown together by a third grader, but also notice that
> the distances include "reaction distance recommended by the National
> Safety Council" which probably assumes a .7 second or greater RT (i.e.
> brain dead) - another common inaccuracy with such graphs.

You ought to read how they determine reaction times in the AASHTO "Green
Book." They say the average reaction time for a driver is around *2*
seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
think that it's unreasonable. Even the Bosch Automotive handbook states
that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

Arif Khokar wrote:

> Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice
>> that the distances include "reaction distance recommended by the
>> National Safety Council" which probably assumes a .7 second or greater
>> RT (i.e. brain dead) - another common inaccuracy with such graphs.
>
>
> You ought to read how they determine reaction times in the AASHTO "Green
> Book." They say the average reaction time for a driver is around *2*
> seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
> think that it's unreasonable. Even the Bosch Automotive handbook states
> that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

I have been meaning to get a copy of the "green book" for a while but
have never gotten around to it. (actually got a call from an AASHTO
related lab regarding my resume, but the job didn't pay enough for me to
go in for the interview) For the purpose for which it's intended
(highway design) I think an overly conservative figure is appropriate.
When it's used as a doom-and-gloom propaganda tool, however...

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Arif Khokar wrote:

> Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice
>> that the distances include "reaction distance recommended by the
>> National Safety Council" which probably assumes a .7 second or greater
>> RT (i.e. brain dead) - another common inaccuracy with such graphs.
>
>
> You ought to read how they determine reaction times in the AASHTO "Green
> Book." They say the average reaction time for a driver is around *2*
> seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
> think that it's unreasonable. Even the Bosch Automotive handbook states
> that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

I have been meaning to get a copy of the "green book" for a while but
have never gotten around to it. (actually got a call from an AASHTO
related lab regarding my resume, but the job didn't pay enough for me to
go in for the interview) For the purpose for which it's intended
(highway design) I think an overly conservative figure is appropriate.
When it's used as a doom-and-gloom propaganda tool, however...

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Arif Khokar a écrit :
> Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice
>> that the distances include "reaction distance recommended by the
>> National Safety Council" which probably assumes a .7 second or greater
>> RT (i.e. brain dead) - another common inaccuracy with such graphs.
>
>
> You ought to read how they determine reaction times in the AASHTO "Green
> Book." They say the average reaction time for a driver is around *2*
> seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
> think that it's unreasonable. Even the Bosch Automotive handbook states
> that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

Hmmm... 2 seconds?

(driving at 75mph)
Alright, the truck in front of me has stopped.
Hmmm... the truck is not moving forward.
Maybe I should change the ringtone on my cellphone.
Hey kids, shut up back there!
Truck is still stopped, maybe I should do something.
Nah
Maybe
(foot off accelerator)

!!

--
----------------------
http://www.saab-900.tk
The Saab Tech Resource
----------------------

Arif Khokar a écrit :
> Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice
>> that the distances include "reaction distance recommended by the
>> National Safety Council" which probably assumes a .7 second or greater
>> RT (i.e. brain dead) - another common inaccuracy with such graphs.
>
>
> You ought to read how they determine reaction times in the AASHTO "Green
> Book." They say the average reaction time for a driver is around *2*
> seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
> think that it's unreasonable. Even the Bosch Automotive handbook states
> that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

Hmmm... 2 seconds?

(driving at 75mph)
Alright, the truck in front of me has stopped.
Hmmm... the truck is not moving forward.
Maybe I should change the ringtone on my cellphone.
Hey kids, shut up back there!
Truck is still stopped, maybe I should do something.
Nah
Maybe
(foot off accelerator)

!!

--
----------------------
http://www.saab-900.tk
The Saab Tech Resource
----------------------

On Sun, 02 Jan 2005 02:17:24 GMT, Arif Khokar >
wrote:

>Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice that
>> the distances include "reaction distance recommended by the National
>> Safety Council" which probably assumes a .7 second or greater RT (i.e.
>> brain dead) - another common inaccuracy with such graphs.
>
>You ought to read how they determine reaction times in the AASHTO "Green
>Book." They say the average reaction time for a driver is around *2*
>seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
>think that it's unreasonable. Even the Bosch Automotive handbook states
>that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

I haven't check it in a while but my memory was that it was
PERCEPTION-REACTION time, not just reaction time. In any event, it's
going to be conservative. If you go thru their various design
requirements you find that they assume a usable coefficient of
friction for design purposes of around 0.25, which is quite low
compared to what's typically the case, however it is about right if
you assume the worst case.
--
Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the
establishment of a standing army, the bane of liberty. . .
Whenever Government means to invade the rights and liberties of
the people, they always attempt to destroy the militia, in order
to raise a standing army upon its ruins." -- Debate, U.S. House
of Representatives, August 17, 1789

On Sun, 02 Jan 2005 02:17:24 GMT, Arif Khokar >
wrote:

>Nate Nagel wrote:
>
>> I just took a look at the graph from the original post and yes it does
>> look like it was thrown together by a third grader, but also notice that
>> the distances include "reaction distance recommended by the National
>> Safety Council" which probably assumes a .7 second or greater RT (i.e.
>> brain dead) - another common inaccuracy with such graphs.
>
>You ought to read how they determine reaction times in the AASHTO "Green
>Book." They say the average reaction time for a driver is around *2*
>seconds, which is total bull**** IMO. As for 0.7 second figure, I don't
>think that it's unreasonable. Even the Bosch Automotive handbook states
>that the average reaction time is around 0.8 to 1.2 seconds, IIRC.

I haven't check it in a while but my memory was that it was
PERCEPTION-REACTION time, not just reaction time. In any event, it's
going to be conservative. If you go thru their various design
requirements you find that they assume a usable coefficient of
friction for design purposes of around 0.25, which is quite low
compared to what's typically the case, however it is about right if
you assume the worst case.
--
Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the
establishment of a standing army, the bane of liberty. . .
Whenever Government means to invade the rights and liberties of
the people, they always attempt to destroy the militia, in order
to raise a standing army upon its ruins." -- Debate, U.S. House
of Representatives, August 17, 1789

In article <_oIBd.7865$wu4.773@attbi_s52>,
Brent P > wrote:
>In article >, Jack Brown wrote:
>> http://www.nydmv.state.ny.us/dmanual/stopdist.gif
>
>It probably should be 103ft, which would be correct on the graph.
>193ft from 55mph is horrid stoping power. A hyundai takes that long to
>stop from 70mph. And it's one of the below average performing cars from
>70mph in the C&D road test digest. There is no way 193ft is the average
>of todays cars from 55mph.

If you look at the nose of the vehicle graphics, they match up with the
distances given (i.e. the nose of the car graphic is at 193 feet).

193 feet is absurdly long for any modern car stopping from 55mph.
However, they may be including reaction time / distance -- i.e. the
distance traveled from when the driver can see that s/he needs to stop
to the time s/he hits the brakes. I.e. if the driver has a 1.1 second
reaction time, then 90 feet traveled during the 1.2 seconds + 103 feet
of braking distance adds up to 193 feet.

Also consider that the "average" car driver includes those distracted (by
cell phones or other things) or not paying much attention to driving at
all. And that the "average" car in service may include those running
on 8 year old waterlogged brake fluid, underinflated mismatched tires, etc..

--
------------------------------------------------------------------------
Timothy J. Lee
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