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Re: NMA STUDY



In article <3ut2ct$8e5@news-e1a.megaweb.com>, kennystar@megaweb.com 
(KENNY MORSE) writes:
> My "analysis" is NOT based on any other factor than EXACTLY what people
> have done to land in my classes over the years....not a "study" where figures
> inevitably get skewed towards the bias of the author, or people just plain
> lie when surveyed.

Ah.  The Tignor and Warren study is not based on surveys.  It is based 
on a multi-year program of *actually measuring* driver behavior.  In 
part, it took advantage of speed zoning changies already being done by 
various state and local agencies, to determine the affects of changed 
speed limits on driver behavior than accidents.  

I urge you to go READ THE PAPER before criticizing it further.  A 
preliminary report appeared in the Institute of Transportation 
Engineers (575 School St., S.W., Suite 410, Washington, D.C.) _ITE 
1990 Compendium of Technical Papers_.  Tignor is the chief of the 
Traffic Safety Research Division of the Federal Highway 
Administration.  

> Since we have no higher speed limit in this country than 65, this is what I
> have found from the real people...not a study:  In 65 zones, people average
> from 70-85.  Since everybody agrees that 55 is not acceptable to them, one 
> would think that when they get into that 65 zone, they THEN would adhere to 
> it.  They don't.

1.  Isn't *your* sample just a tad bit biased toward speeders?  Those are 
the ones that are in your class, after all!  

2.  Yes, lots of people drive faster than 65.  This does not imply 
that, *if* the 85th percentile speed was used to set the limit on 
65-mph roads, that lots of people would drive faster on those roads.  

Personal experience: I've been driving the I-5 between here and San
Francisco for over twenty years.  I've driven it when it was
sign-posted at 70; when it was sign-posted at 55; and now when it's 
sign-posted at 65.  The typical speed on that road has been 75-80 for 
the entire twenty years.  NOT because it's n mph over the speed limit, 
but because that's what feels comfortable and safe to most drivers.  

> I agree with the assertion that setting a speed where everybody is encouraged to 
> do the same speed most CERTAINLY lower accidents.  BUT....and this is
> a BIG but......that assumes that people will behave in OTHER manners that
> won't contribute to a crash.  Here in California, the #1 cause of crashes is
> tailgaiting.....EVEN IN 65 ZONES!!!!!!  If everybody wouldn't tailgate (because
> they're in such a hurry), if people wouldn't run red lights (#1 cause of city street
> death in cars), and if people wouldn't drink & drive, or weave lanes, then a
> sanely set speed that ALL people whould respect and follow would work.

First, let's agree to strike the ALL from that last sentence -- you'll 
never find one limit that ALL people will respect.  Can we agree on 
the 85th percentile speed, as advocated by the T&W study? 

Ok, given that, I'll stipulate for sake of argument that raising the
speed limit to the 85th percentile speed would not reduce accidents. 
That does not imply that it isn't worthwhile to so raise the speed
limit.  Raising the speed limit on most roads to the 85th percentile
speed would have several very large benefits: 

1.  Speed enforcement could be targeted at drivers who arec clearly at 
risk.  (In the T&W study, "the accident involvement rates on streets 
and highways in urban areas was highest for *the slowest 5%* of the 
traffic [emphasis mine], lowest for traffic in the 30-95%tile range, 
and increased for the fastest 5% of the traffic.)  The posted limits 
currently make violators out of motorists driving at reasonable and 
safe speeds.  

2.  Where it is necessary to post a lower speed due to special 
conditions, drivers might actually comply with it... if they weren't 
used to most speed limits being set too low.  

By the way, "Mr. Traffic", I'll happily fax you a copy of the
preliminary findings (just one page, though of very fine print) of the
Tignor and Warren study.  It sounds like something you really ought to
read, considering your line of work and claimed area of expertise, if
only so you can refute it knowledgeably.  (Your claim about "people
lie when surveyed" is wildly off-point, for example, since no drivers
were actually interviewed for the study.)  Just e-mail me your fax
number.  

	--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
Internet: jeh@cmkrnl.com (JH645)  CompuServe: 74140,2055  


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