Chicago Court Throwing Out LIDAR Speeding Tickets 245
bridgeco writes "Chicago Traffic Court Judges have been throwing out speeding cases in which the driver's speed was measured with a LIDAR. Judges are asking for a special 'Frye Hearing' to determine the accuracy of these devices. Many motorists nabbed for speeding by a laser gun, instead of radar, are seeing their tickets thrown out at Chicago's traffic court because of a legal issue that the city's law department has been unable to overcome. Within the past year judges in Cook County Traffic Court in Chicago determined that speeds captured by lidar were not admissible because the devices had not been proven scientifically reliable in an Illinois court, said Jennifer Hoyle, spokeswoman for the law department, which prosecutes most speeding tickets in the city." (Here's some background on LIDAR from Wikipedia.)
link from search (Score:2, Informative)
http://www.chicagotribune.com/news/chi-speeding-tickets-09-nov09,0,7869040.story
Hawaii has the same issue (Score:5, Informative)
Working link to article (Score:3, Informative)
http://www.chicagotribune.com/news/chi-speeding-tickets-09-nov09,0,7869040.story [chicagotribune.com]
Yeah, but it is reliable. (Score:4, Informative)
Fixed Link (Score:2, Informative)
Re:Yeah, but it is reliable. (Score:3, Informative)
LIDAR is about as reliable as your imagination. Go research how it works and you'll see, moving objects are not what lidar is for at all. It's just a poor attempt at shoehorning a measurement device that has a monopoly in chicago basically.
Comment removed (Score:5, Informative)
Re:Yeah, but it is reliable. (Score:4, Informative)
RADAR isn't always accurate either, as the beam is wider and can't discriminate between different vehicles. It will always give a correct speed, but not necessarily that of the correct target.
An easy solution would be to capture video of the lazer on the target for every pull. Then compare the data points to the photos of the lazer beam. If there's an excursion, throw the ticket out.
LIDAR generally is less accurate... (Score:5, Informative)
...in that because its beam is so narrow, that the speed measured is more precisely the speed measured between the target vehicle and the LIDAR gun itself, not necessarily the forward speed of the target vehicle down the road. Since the patrol officer is always sitting off the side of the road, that introduces what's known as the "cosine error" which is actually in the speeder's favor since the LIDAR device will show the officer a slower speed (vehicle's actual forward speed times the cosine of the angle between straight ahead vs a line between the front of the vehicle and where the officer's LIDAR is actually located). Most of the time, the cosine error is negligible, but if the officer is sitting far enough off the side of the actual roadway and the angle is big enough, the cosine error can be several MPH in the speeder's favor.
Radar POP mode (Score:5, Informative)
"POP is mode that emits a very brief (67 millisecond) pulse of radar to determine the speed. Its meant to defeat radar detectors. It works because the local oscillator sweep (the "tuner") in most detectors, (especially cheap ones) is too slow to notice this brief pulse. Newer and more expensive detectors have solved this by making a little detour during the sweep to check for POP. It's like flipping through the channels on your TV, but going back to check if your favourite show has started on channel 2 every so often. Except in a radar detector this is happening hundreds of times per second.
POP can be inaccurate because the electronics in the police radar don't have time enough to stabilize. It's like suddenly jumping on your bathroom scale. The pointer with fluctuate violently until it settles down on the the true reading. With POP it can sometimes indicate an inaccurate speed due to this instability. "
Re:Yeah, but it is reliable. (Score:3, Informative)
RADAR isn't always accurate either, as the beam is wider and can't discriminate between different vehicles. It will always give a correct speed, but not necessarily that of the correct target.
Yup, if you're in a group of cars, you're safe from RADAR alone, as an old cop friend of mine once told me. They can't really tell what they just got a speed reading of. OTOH, the cops can usually tell when you're speeding without RADAR. They (or at least one of them) use the RADAR to collect objective evidence, not to identify the speeder, they've already done that before they reach for the RADAR gun.
Re:Oh noes news at 11 (Score:1, Informative)
Nope. Real judges down here in traffic courts. "Traffic court" in Cook County includes everything from petty tickets through Class A misdemeanors (DUIs).
Re:We don't have equipment at that frequency? (Score:3, Informative)
Just modulate the beam: Turn it off, and back on at a known, sane interval.
When the interval varies (due to doppler shift), measure the difference in frequency.
Done.
No DC-to-daylight processing of gee-whiz THz signals required. The the carrier frequency (the frequency of the laser beam, in this case) is not important for this to work, as long as you can reliably detect its modulation. Many of these parts must already be in use in existing LIDAR systems, so that the machine can discriminate between its own little point of light and all the background noise around it (daylight).
It's all pretty simple, old-hat tech. Plain old regular amplitude modulation, as described above, would be fine, but there's a lot of other methods [wikipedia.org] which might work just as well.