Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!sdd.hp.com!hp-pcd!hp-vcd!johne
From: johne@hp-vcd.HP.COM (John Eaton)
Newsgroups: sci.electronics
Subject: Re: IR receiver on traffic lights ?
Message-ID: <2470017@hp-vcd.HP.COM>
Date: 12 Apr 91 16:53:40 GMT
References: <1991Apr11.211957.7309@lynx.CS.ORST.EDU>
Organization: Hewlett Packard, Vancouver, WA
Lines: 20

<<
< The fire trucks in my town seem to trip traffic lights to green in
< their direction as they are approaching the intersection.  Does anyone
< know how they do this?  I thought they might have a system using
< Dean Youngquist                 youngqd@jacobs.cs.orst.edu
< Corvallis, Oregon 97330         Tel. (503) 757-0335
----------
If you examine the stop lights you will see a small "probe" that points
towards oncoming traffic. This probe detect the emergency lights and
switches the light green in that direction. The key light is not the
normal red flashers but rather a single Xenon strobe light that all
emergency vechicles in the town have mounted in front. (And you thought
that was there to get YOUR attention?). I figured this out one day when
I was waiting for a left turn signal (On ninth street in Corvallis), when
an ambulance approached the light with ONLY the strobe light flashing.
The light gave that direction immediate clearance. I suspect that it keys
in on a certain rep rate for a flashing light.

John Eaton
!hp-vcd!johne