Radar - Stronger vs. Faster <long>

[SMILLER@xxxxxxxxxxxxxx]

John, in case no one else challenged you on this, I just have to bring it
up.

>Date: Mon, 19 Oct 1998 00:18:27 -0700
>From: John Fountaine <jfount@domain.elided>
>Subject: Re: bmw-digest V9 #345
[major snipage]
> I am sure you know that the radar will pick up the target moving the
>fastest.  This changes at great distances, especially when there are
>other vehicles with considerably more mass, (ie I may not pick up a
>speeding motorcyclye until it is much closer than the cars it is
>approaching with, likewise I may not pick up a car at a great distance
>when it is surrounded by 18 wheelers.

You're saying that the laws of physics change with distance.  You're
saying that, at close range, the radar unit picks up the signal of the
fastest vehicle, but at greater distances, other factors come into play.

I don't think so.  The radar unit sends out a radio signal.  That radio signal
bounces off of various objects.  (The speed of those objects shifts the
frequency of the reflected signal - doppler effect - and the radar unit
then compares the frequency of the reflected signal with the original
frequency to determine speed.)  Some of the reflected signals are strong
enough for the radar unit to receive.  Of all the received signals, the
radar unit locks onto the STRONGEST signal.  The strength of the signal
is determined by the frontal area and material composition of the object,
and  proximity to the radar unit.  Unless there are new developments in
traffic radar that I don't know about (and there very well could be), there
is nothing in the radar unit that picks up the signal of the vehicle that is
moving the fastest.  If several vehicles are moving in a "pack", they are
all reflecting a signal, but only one is the strongest.  It isn't necessarily
the fastest.

You do make an excellent point about making a visual estimate of the
speed, all officers that I've heard talk about this say the same thing.  The
radar just confirms what you see, unless, of course, visibility isn't good
enough to make an accurate estimate.

[OK, that's the end of the important part, the rest is just basically some
<wob> that backs up my point.]

Personal experience - the speeding ticket I received in Castro Valley, CA
(mentioned in a previous post).  I was eastbound on Crow Canyon Road
(in my 1977 630csi on my way to a GGC drivers' school - obligatory
content).  Coming from the freeway, there are 2 lanes in each direction,
but where the road enters the actual canyon, it narrows to 1 lane in
each direction.  The game here is to go fast enough to be the first car
into the canyon so you can enjoy the twisties, but not too terribly fast.  I
had my Yoko A008RS tires on, which were smaller diameter than the
stock tires, and I had checked and double checked and tripple checked
my speedometer accuracy with these tires.  I was going between 45
and 47 in a 35 MPH zone (speedometer reads 5 MPH higher than actual
speed), and I know that I wasn't going faster.  

In the pack right behind me were all kinds of other vehicles, cars,
pickups, vans, trucks, and I was going just fast enough to stay in front of
them.  It was dark, so I didn't see the CHP in the median using radar.  My
"trusty" Passport detector wasn't working and gave no warning.  When
the CHiPpie stopped me, he told me he locked me in at 58 MPH.  Now I
KNOW that I was only going between 45 and 47, and I KNOW that he got
a lock on one of the vans or trucks that were right behind me who were
all probably trying to speed up at that point to be the first into the canyon
(that's what EVERYONE does there, even if they're driving crap and
know they'll be slowing everyone down in the turns).  But what could I
say?  I also knew that I was speeding, and it didn't make that much
difference if I was going 47 or 58.  The only thing I don't know is exactly
how far out I was when he locked in  the speed.  It was less than a
quarter mile, based on the distance from the exit of the curve to the place
the CHP officer was parked in the median.  But, a bunch of vehicles
came around the curve and down the hill and he saw 58 and then he
saw me in front.  (A visit to commedy traffic school wiped out the record
of the ticket with no conviction, so my insurance was safe.)

I must say, the CHP officer was nice about the whole thing.  When he
said he used radar, I said he must be mistaken because my detector
never went off (OK, I shouldn't have even mentioned it).  After writing
the ticket, he was nice enough to trigger the radar unit again from less
than 30 feet away, and the detector still remained silent.  He suggested
getting it fixed, since it represended a significant investment and was
obviously broken.  He could have given me a lecture about even having a
detector, but he didn't.  I thought that was cool.

OK, so remember, barring any new technology that ignores stronger
signals and locks in faster ones, the laws of physics still apply,
regardless of the distance from the radar unit.  Right?  (Go on, Digesters,
flame away, what do I know?)

Scott Miller
GGC BMW CCA #44977
1990 325i/is hybrid with Solo 5

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