From: bpita@ctp.com (Bob Pitas)
Subject: Re: Tailgaters abound!
Date: Thu, 27 Aug 1992 18:21:55 GMT
Organization: Cambridge Technology Partners

In article <BtCqEw.2y2@news.cso.uiuc.edu> tmkk@uiuc.edu (Khan) writes:
>
>In article <1992Aug20.170518.11698@cbfsb.cb.att.com> ashaw@cbnewsg.cb.att.com (andrew.shaw) writes:
>>From article <Bt9CHH.I4n@news.cso.uiuc.edu>, by khan@mrcnext.cso.uiuc.edu (Scott Coleman):
>>> derek@nezsdc.icl.co.nz (Derek Tearne) writes:
>>> 
>>>>"Only a fool breaks the TWO second rule".  It rhymes, it fits it's easily
>>>>rememberable.  
>>> 
>>> Actually, it's only a 2-second rule up to maybe 45MPH, after which you're
>>> better off with a FOUR second following distance. 
>>
>>I thought the advantage to the 2-second (as opposed to the older
>>n-car-lengths) rule was that it was speed-invariant.  Thus 2 seconds
>>at 30mph gives you 88 feet to stop in, while 2 seconds at 60mph gives
>>you 176 feet.
>
>Let's examine this statement more closely.
>
>According to a recent test of four sports cars by Consumer reports(*), a
>Mazda RX-7 has a braking distance of 119 feet from 60MPH. This distance
>set a record(**) for the shortest stopping distance, so it's safe to say
>that 119 feet is a MINIMUM figure - chances are your car will take
>longer to stop on dry pavement at 60MPH. So, with your following
>distance of 176 feet, that gives you 176-119 = 57 feet in which to
>react, or 0.647 seconds to a) assess the situation, and b) move your foot
>from the gas to the brake. And that's only if you're driving an RX-7; if
>you're in a Corvette with ABS, you'll have 176-126 = 50 feet = 0.568
>seconds to react. And God help you if you're driving a car with poorer
>braking performance than a $30,000 sports car, or you're driving in the
>rain, or if you're a little bit tired, or...
>
>Now you see why a 4 second following rule is a NECESSITY at higher
>speeds.
>
>
>(*) September 1992 issue, if you want to check my facts for yourself.
>
>(**) What this means exactly was not explained in the article, but I
>assume that the RX-7 was either the fastest stopping car CR has ever
>tested (as opposed to the fastest stopping car ever reported in an
>independent test).
>

Duh?  If the car in front of you could stop instantaneously, you're
observations above would be correct.  As it turns out, you can be 1cm from
the car in front of you, as long as you can instantly react, and your brakes
are as good or better as the brakes of the car in front of you, you won't
hit them!  Just remember that the car in front of you takes just as long
as you do to stop, so unless you're talking about coming around corners
and suddenly finding stationary objects in your path, you have roughly
twice the distance you outlined.



----------------------------------------------------------------------------
        ___          
       / _ \                 '85 Mustang GT                        Bob Pitas
      /    /USH              14.13 @ 99.8                      bpita@ctp.com
     / /| \                  Up at NED, Epping, NH           (Cambridge, MA)

"If you go fast enough, driving in traffic is like driving in a parking lot"
Disclaimer: These opinions are mine, obviously, since they end with my .sig!
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From: ggg@hpsad.sad.hp.com (Gary Goodlund)
Date: Mon, 31 Aug 1992 21:42:35 GMT
Subject: Re: Electronic Counter Measures
Organization: HP Signal Analysis Division - Rohnert Park, CA