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From: ark@rabbit.UUCP
Newsgroups: net.physics
Subject: Re: Car detectors at fast-food joints
Message-ID: <2232@rabbit.UUCP>
Date: Tue, 29-Nov-83 15:15:55 EST
Article-I.D.: rabbit.2232
Posted: Tue Nov 29 15:15:55 1983
Date-Received: Thu, 1-Dec-83 03:22:58 EST
References: <1092@ucf-cs.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 5

There is a metal horn much like what you describe on a lamp post
at the intersection of Riverside Drive and West 115th Street in
New York City.  The horn detects cars in order to control the
traffic lights at the intersection.  It works by sound:  I can hear
the chirps it emits.