snopes.com  


Go Back   snopes.com > Urban Legends > Automobiles

Reply
 
Thread Tools Display Modes
  #1  
Old 17 January 2013, 05:17 AM
hoitoider's Avatar
hoitoider hoitoider is offline
 
Join Date: 22 October 2001
Location: Virginia Beach, VA
Posts: 5,950
Police Radar guns inaccurate in rain?

I had always heard that the police can't use radar guns in the rain because it gives an inaccurate reading. Then today I saw a cop parked in the median of the interstate using one in a pretty good downpour. Perhaps I believed a UL all these years? Googling provides answers both ways. This vendor's site has on their FAQ:

Quote:
(Q)Does weather effect radar?
(A)Yes. Weather mainly effects radar detection range. X band radars operate better than K or Ka band radars in bad weather. Water in the atmosphere (humidity and rain) effects K band radars the most, Ka band radars transmissions are also effected. X band radars to a lesser degree.
I can't really interpret that as per the law but I'm wondering if the cop today was wasting his time.
Reply With Quote
  #2  
Old 17 January 2013, 05:26 AM
UEL's Avatar
UEL UEL is offline
 
Join Date: 01 August 2004
Location: Gloucester, ON
Posts: 7,020
Baseball

This is just a quick thought off the top of my head. I do work with radars, however, not the type used by police. But emitted radar energy behaves the same largely independent of the type of radar emitting it.

There are some wavelengths that are horrible in rain, or snow, or sand. Others are fine.

In one of our radars, our detection range is reduced by about 12% (range and radar not identified for my own reasons). Everything up to the reduced maximum range is still as accurate as ever.

Your observed police officer may very well have reduced range, but unless his maximum range was reduced to mere metres, I would submit that he would still have enough space to get his required readings to issue a ticket.
Reply With Quote
  #3  
Old 17 January 2013, 05:56 AM
erwins's Avatar
erwins erwins is offline
 
Join Date: 04 April 2006
Location: Portland, OR
Posts: 9,251
Default

Also, a significant portion of the "radar" guns you see police using these days are actually laser based, not radar based. I don't know if those are affected by rain either, but seeing an officer using a speed measuring gun doesn't automatically mean they are using radar.
Reply With Quote
  #4  
Old 17 January 2013, 06:04 AM
crocoduck_hunter's Avatar
crocoduck_hunter crocoduck_hunter is offline
 
Join Date: 27 May 2009
Location: Roseburg, OR
Posts: 7,188
Default

What's the normal effective range of one of those devices?
Reply With Quote
  #5  
Old 17 January 2013, 06:28 AM
geminilee's Avatar
geminilee geminilee is offline
 
Join Date: 02 December 2005
Location: New Orleans, LA
Posts: 11,236
Default

Quote:
Originally Posted by hoitoider View Post
I can't really interpret that as per the law but I'm wondering if the cop today was wasting his time.
If the radar gun was visible, like held out a window or something, his main purpose might not be to ticket people but to get them to slow down in dangerous conditions, for fear of getting a ticket. IOW, he could just have been bluffing.
Reply With Quote
  #6  
Old 17 January 2013, 02:10 PM
Not_Done_Living's Avatar
Not_Done_Living Not_Done_Living is offline
 
Join Date: 02 September 2006
Location: Markham, ON
Posts: 3,261
Default

in my neighborhood, as you enter the "school zone" there is a large sign that reports your speed back to you a a reminder -- it normally tracks for about 500 meters. in rain, in snow, night or day -- i have not seen a difference -- as soon as i can see it, it can see me --

i am pretty sure its not some super high tech device ---
Reply With Quote
  #7  
Old 17 January 2013, 06:40 PM
jimmy101_again jimmy101_again is offline
 
Join Date: 29 December 2005
Location: Greenwood, IN
Posts: 5,166
Default

Quote:
Originally Posted by Not_Done_Living View Post
in my neighborhood, as you enter the "school zone" there is a large sign that reports your speed back to you a a reminder -- it normally tracks for about 500 meters. in rain, in snow, night or day -- i have not seen a difference -- as soon as i can see it, it can see me --

i am pretty sure its not some super high tech device ---
Actually, it probably is a super-high tech device. But super-high tech devices can be made for a couple hundred bucks (see iPhones, laptops, ...)
Reply With Quote
  #8  
Old 17 January 2013, 08:18 PM
Hero_Mike's Avatar
Hero_Mike Hero_Mike is offline
 
 
Join Date: 06 April 2005
Location: Phoenix, AZ & Hamilton, ON
Posts: 7,268
Default

What UEL said. Different atmospheric conditions will affect different wavelengths. Fog or mist might be the worst because of its density, but that all depends on how "thick" the air is with moisture. FWIW, my radar detector consistently warns me of only laser and Ka band down here in Arizona when near police, though X and K are found in automatic doors in parking lots and the detector reports those faithfully as well. I have no proof, but I strongly suspect that police here only use Ka band (with respect to "radar"). That being the case, I got a warning for speeding on the 4th of July last year, on a rare rainy day. The radar performance was, apparently, not affected enough to matter to the deputy who have me the warning. I did not have my detector that day, and was not watching my speed on the long, straight road into my subdivision (speed limit 45).
Reply With Quote
  #9  
Old 18 January 2013, 06:25 AM
Meka Meka is offline
 
Join Date: 20 December 2006
Location: Buffalo, NY
Posts: 925
Default

Quote:
Originally Posted by erwins View Post
Also, a significant portion of the "radar" guns you see police using these days are actually laser based, not radar based. I don't know if those are affected by rain either, but seeing an officer using a speed measuring gun doesn't automatically mean they are using radar.
I can't speak to laser speed guns specifically, but I have had experience with lasers being affected by rain, specifically heavy rainfall inadvertently triggering the timing lights at autocrosses. However, those lasers are intended to function over distances of just a few yards, so I suspect an officer's laser would be more powerful, and therefore more capable of penetrating a rainstorm.
Reply With Quote
  #10  
Old 18 January 2013, 07:55 AM
Troberg Troberg is offline
 
 
Join Date: 04 November 2005
Location: Borlänge, Sweden
Posts: 11,404
Default

My guess is that the policeman simply did not know the limitations of his tool, or simply didn't care. At least, it's common enough here for them to behave like that.
Reply With Quote
  #11  
Old 18 January 2013, 05:34 PM
hambubba's Avatar
hambubba hambubba is offline
 
Join Date: 30 June 2000
Location: Gonzales, LA
Posts: 10,716
Default

The reason weather radar works, is based on the reflection of the water droplets. A droplet reflects the signal, some drops reflect more, all based on the wavelength of the signal.

This varies with type of radar, etc. Higher frequency devices need much smaller drops to get a full reflection. A big drop, oh, say "car-sized" wouldn't be much of a problem even with the rain. fog would be the worst culprit.

For you math geeks out there, this might be some help.
Reply With Quote
  #12  
Old 20 January 2013, 04:21 AM
TB Tabby TB Tabby is offline
 
Join Date: 13 January 2004
Location: Bolingbrook, IL
Posts: 1,714
Default

So I can get away with speeding when visibility is poor and the roads are slick! Awesome! I see no downside to this!
Reply With Quote
  #13  
Old 20 January 2013, 04:29 PM
DawnStorm's Avatar
DawnStorm DawnStorm is offline
 
Join Date: 11 March 2003
Location: Montgomery County, MD
Posts: 12,716
Police

Would this apply to speed cameras? Just recently the Baltimore Sun did a big study on how accurate Baltimore City cameras were and the results were not pretty. The company claimed that environmental conditions affected the accuracy and that the cameras worked fine. Naturally the City defended the cameras.
Here is one article about the issue.
And another one.
Reply With Quote
  #14  
Old 22 January 2013, 08:29 PM
Wintermute's Avatar
Wintermute Wintermute is offline
 
 
Join Date: 04 July 2003
Location: Walnut Creek, CA
Posts: 6,535
Default

Quote:
Originally Posted by erwins View Post
Also, a significant portion of the "radar" guns you see police using these days are actually laser based, not radar based. I don't know if those are affected by rain either, but seeing an officer using a speed measuring gun doesn't automatically mean they are using radar.
Maybe it's a regional thing but LIDAR isn't THAT common. It's a very expensive tool and the RADAR units have already been purchased. Working in the east bay the only time I saw a LIDAR unit was when I went to the training course for it.

LIDAR is affected by rain. It's a light beam. So fog, rain, smoke, etc will shorten the effective distance.

It's ironic that people always try to fight speeding ticket based on RADAR by googling things on the internet. Most errors cause by RADAR technology actually show a DECREASE in speed and not an increase in speed.

The best way to beat a RADAR ticket is ask for the logs for the RADAR gun. It's common the officer either does not test the unit or does not document the testing of the unit. At least in California it's expected to be done at the start of the shift and at the end of the shift.
Reply With Quote
  #15  
Old 24 January 2013, 01:37 AM
RichardM RichardM is offline
 
Join Date: 27 March 2004
Location: Sachse, TX
Posts: 3,183
Default

The logs are not generally available throughout the country nor is the officer likely to have them available at the time the ticket is being issued. The logs can be subpoenaed by your lawyer if needed.
Richard (who is known to drive fast)
Reply With Quote
  #16  
Old 10 December 2013, 07:18 PM
snopes's Avatar
snopes snopes is offline
 
Join Date: 18 February 2000
Location: California
Posts: 108,824
Cow

Comment: I heard that the ornamental "bull balls" that you see people hang
from the back bumper of their trucks (or other model vehicles) can throw
off the results of a police radar detector gun or scanner. That can't be
true, and if it is, it would have to be a specific brand designed for that
purpose, right?
Reply With Quote
  #17  
Old 10 December 2013, 08:59 PM
RichardM RichardM is offline
 
Join Date: 27 March 2004
Location: Sachse, TX
Posts: 3,183
Default

The reply to that is contained in the query. Bull!
Reply With Quote
  #18  
Old 16 March 2014, 01:24 PM
mobocracy mobocracy is offline
 
Join Date: 11 February 2014
Location: Minneapolis, MN
Posts: 5
Default

Quote:
Originally Posted by Wintermute View Post
Maybe it's a regional thing but LIDAR isn't THAT common. It's a very expensive tool and the RADAR units have already been purchased. Working in the east bay the only time I saw a LIDAR unit was when I went to the training course for it.
I mostly see highway patrol and cops using laser these days -- they have to aim it and most appear to be looking through it like some kind of scope, which would make sense because it would need to be pointed right at whatever they're trying to get a speed reading, whereas RADAR would have a wider beam.

In addition to weather interference, I think you don't see it used in the rain because the device and the officer need to be exposed to the weather.

As for accuracy of any of it in rain, I think the first goal is simple intimidation making people think you're getting a reading even if you're not. And I'm cynical enough to believe that many cops would pull someone over and claim they were speeding whether they had a valid reading or not.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
The Rain BrianB Glurge Gallery 20 30 September 2011 04:39 AM
Fireworks cause rain snopes Old Wives' Tales 3 22 August 2009 06:02 PM
Canadians shut down early warning radar for the weekend snopes Military 5 24 November 2008 09:59 PM
Hot Wheels ad for radar gun inappropriate for kids snopes Inboxer Rebellion 4 19 September 2007 04:56 PM
Did cops receive radar guns from insurance companies? DawnStorm Automobiles 21 18 April 2007 04:11 PM


All times are GMT. The time now is 11:01 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.