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From: bill@utastro.UUCP (William H. Jefferys)
Newsgroups: net.bicycle
Subject: Re: left turns
Message-ID: <292@utastro.UUCP>
Date: Fri, 28-Jun-85 13:04:59 EDT
Article-I.D.: utastro.292
Posted: Fri Jun 28 13:04:59 1985
Date-Received: Wed, 3-Jul-85 06:17:39 EDT
References: <605@intelca.UUCP> <1636@reed.UUCP> <328@varian.UUCP> <2@uw-june>
Organization: U. Texas, Astronomy, Austin, TX
Lines: 35

> 
> > >1) most left turns around here have sensors in the street, so they don't
> > >	change unless something large and metalic is sitting on them.
> > 
> > It angers me however that the state can declare a bicycle a vehicle
> > and then interfere with its safe and efficient operation with these
> > ridiculous sensors.  My motorcyclist friends have the same problem,
> > incidentally.  Does anyone know if these sensors have adjustable 
> > sensitivity?  They are based on a metal object interfering with a
> > magnetic field, so I should think so.
> > 
> In fact, these sensors are adjustable, but if the sensitivity is made
> too high, a really massive piece of metal (like a truck)
> can activate the one in the adjacent lane.  This can cause problems
> like a left-turn signal going on when no one is waiting to make a left
> turn!  So you see, it's not quite as simple as it seems at first.
> 
Actually, there is a way around this, but it has to be done when the
sensor loop is *installed*.  (Described in John Forester's *Cycling
Traffic Engineering*):  If the loop is installed as a figure 8
instead of (as is normal) a plain loop, it will simultaneously become
more sensitive to low-mass objects such as bicycles over it, and
less sensitive to large objects, such as trucks, in the adjacent
lane.  Unfortunately, very few of the people responsible for installing
these things are aware of this.  It is really up to bicyclists to
organize and make waves at city hall!

-- 
"Men never do evil so cheerfully and so completely as when they do so from
	religious conviction."  -- Blaise Pascal

	Bill Jefferys  8-%
	Astronomy Dept, University of Texas, Austin TX 78712   (USnail)
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