Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84 exptools; site ihuxe.UUCP
Path: utzoo!linus!decvax!harpo!whuxlm!whuxl!houxm!ihnp4!ihuxe!chas
From: chas@ihuxe.UUCP (Charles Lambert)
Newsgroups: net.auto
Subject: Misuse of Radar - a case history
Message-ID: <1213@ihuxe.UUCP>
Date: Wed, 14-Aug-85 14:22:24 EDT
Article-I.D.: ihuxe.1213
Posted: Wed Aug 14 14:22:24 1985
Date-Received: Tue, 20-Aug-85 07:49:47 EDT
References: <2493@pegasus.UUCP> <752@dataio.UUCP> <134@drutx.UUCP> <486@busch.UUCP>
Organization: AT&T Bell Laboratories
Lines: 41

[ Excerpt from the "Radar Surveillance" discussion ]
> ...                                              He stopped me for doing 67 
> when I was doing 55 mph. I had my cruise on and was on a flat stretch of the 
> road. Naturally I was pretty upset about the whole thing but decided my speed-
> ometer was out of sync and had it checked for $25. The guy told me it would 
> be one mph off at speeds around *80* mph.  I now live 200 miles from where the 
> ticket was written and didn't have the vacation time or real belief that I 
> could beat this so paid the fine and forgot it.
> 
> ...          Last friday I got stopped for doing 52 in a 35.  Radar again.  I
> absolutely know I wasn't going over 40.

Radar guns are used in Britain and, several years ago, there was an
important test case concerning their incorrect use by police officers.

A driver was pulled up by a police car, shortly after going over the brow
of a hill.  An officer standing by the road with a radar gun had registered
his speed as being over the limit.  The driver in question was certain that
he had been within the limit so he challenged the charge in court.  No luck,
he was fined.  The guy happened to be an Electronic Engineer and determined
to prove that the radar gave a false reading.

At the time of his alleged offence, he remembered another car travelling in
the opposite direction at high speed.  Through a series of tests, conducted
with several models of radar gun, he demonstrated that the signal reflected
from the front of a target car can strike a car travelling in the opposite
direction, return by way of the target car and still be strong enough to
give a false reading.  Depending on the speed-detection method used by the
device, the reading can be either the speed of the secondary vehicle or even
the combined speed of both vehicles.

False readings can also be produced by reflection from large signboards
(such as freeway route signs) onto secondary vehicles.

Using this evidence he successfully appealed his conviction, which was
quashed for unreliable evidence.  Consequently, codes of practice have been
introduced that constrain the circumstances in which a radar gun should be
used (no large standing objects; no adjacent vehicles; etc.) and the
credibility of their evidence severely undermined.

Charlie (the Alien) @ the Death Star, IL.