Five times and counting before three different judges, the Prince George’s County business owner has used a computer and a calculation to cast reasonable doubt on the reliability of the soulless traffic enforcers.
After a judge threw out two of his tickets Wednesday, Mr. Foreman said he is confident he has exposed systemic inaccuracies in the systems that generate millions of dollars a year for town, city and county governments. He wasn’t the only one to employ the defense Wednesday. Two other men were found not guilty of speeding offenses before a Hyattsville District judge during the same court session using the same technique.
“You’ve produced an elegant defense and I’m sufficiently doubtful,” Judge Mark T. O’Brien said to William Adams, after hearing evidence that his Subaru was traveling below the 35-mph limit - and not 50 mph as the ticket indicated.
The method? Mr. Foreman, the owner of Eastover Auto Supply in Oxon Hill, examined dozens of citation photos of his company’s trucks that were issued along a camera-monitored stretch of Indian Head Highway his employees frequently travel. The camera company, Optotraffic, uses a sensor that detects any vehicle exceeding the speed limit by or more miles per hour, then takes two photos of it for identification purposes. The photos are mailed to violators, along with a forty dollar ticket.
For each ticket, Mr. Foreman digitally superimposed the two photos - taken 0.363 seconds apart from a stationary point, according to an Optotraffic time stamp—creating a single photo with two images of the vehicle.
Using the vehicle’s length as a frame of reference, Mr. Foreman then measured its distance traveled in the elapsed time, allowing him to calculate the vehicle’s speed. In every case, he said, the vehicle was not traveling fast enough to get a ticket. So far the judges have agreed.
“I’ve never seen this before,” Judge O’Brien said, as he examined a superimposed photo presented by Mr. Adams, who also employed the technique. “How much time did you spend on this?”
Mr. Foreman said he is awaiting trial on about 40 more tickets, all of which he called “bogus.”
Speed cameras “can be good, but not if they’re abused,” he said after the hearing.
The Maryland General Assembly approved speed cameras in 2009 for school and highway-work zones, two years after a pilot program in Montgomery County. Prince George’s officials have long resisted speed cameras, but many municipalities began implementing them in fall 2009.
Supporters of the devices have argued they reduce speeding over time and increase safety, while many opponents call them a cash cow for local governments.
Mr. Foreman’s tickets were issued in Forest Heights, a town of about 2,600 where officials expected $2.9 million in ticket revenue this fiscal year, about half the town’s $5.8 million budget.
In Prince George’s County, cameras are operated entirely by municipalities, which can set them up within half-mile school zones. The devices are installed by vendors that typically receive about 40 percent of the payout on each ticket, with the rest going to local, county and state government.
Municipalities other than Forest Heights also use Optotraffic cameras. The Lanham-based vendor also serves New Carrollton, Mount Rainier and College Park, as well as the city of Cambridge in Dorchester County, Maryland.
Optotraffic representatives said the photos are not intended to capture the actual act of speeding, and are taken nearly 50 feet down the road from sensors as a way to prove the vehicle was on the road.
“No one has come to us with a proven error,” company spokesman Mickey Shepherd said Tuesday. “Their speed is not measured by the photos. The speed is measured before the photos are taken.”
An Optotraffic technician was sworn in and offered the company’s defense in the courtroom on Wednesday to no avail. Mr. Foreman didn’t buy it either. He said it was unlikely that his vehicles slowed significantly after passing the sensors, as photos typically show them with their brake lights off. While Judge O’Brien let Mr. Foreman off the hook, he ruled against several other accused speeders who based their not-guilty pleas largely on gut feelings that the cameras were flawed, while reducing the fines for some who pleaded guilty.
THE METHOD IN DETAIL: How Did Will Foreman Prove His Innocence? First, Forest Height’s speed cameras are a proprietary design by Optotraffic, a division of Sigma Space Corporation. These cameras are neither radar (like most cameras used in Montgomery County) nor are they exactly like traditional police LIDAR. Technical specifications for Optotraffic’s cameras can be viewed here.
To simplify it, Optotraffic’s cameras work by taking two laser sensors into each lane of traffic. The device “records the time when each sensor detected the object.” The speed is then calculated as “Measured Speed = Distance/Time.” If a vehicle is determined to be exceeding a predefined threshold speed, a short distance/period of time later the device snaps two photos a fraction of a second apart.
So why would someone think the devices are inaccurate? Well, because many people have gotten tickets from Forest Heights for speeds they know they were not traveling at. Some of them performed their own distance/time calculations from the citation images which produced an extremely different speed than what they were cited for.
Speed camera images are typically taken a few tenths of a second apart, so the distances traveled are fairly short (tens of feet). Getting exact distances from photos can be difficult, so it is hard to convincingly prove the speed measurement was in error unless it was off by a large amount. If the speed camera was off by say 5 mph then proving yourself innocent this way would be difficult (and proving yourself innocent is exactly what you would be required to do in court). Assuming large errors are sporadic (as opposed to a device that always produced an incorrect result), any one specific person would be unlikely to get enough citations with extremely large errors to prove the existence of a pattern.
A local business owner, Will Foreman of Eastover Auto Supply in Oxon Hill, maintains a small fleet of vehicles that must drive up and down Indian Head Highway in Forest Heights several times per day and as a result received a large number of citations for that fleet. He later discovered other enraged citizens had also received questionable tickets. Many of the photos clearly show the speed measurements are much higher than the distances traveled between the citation images. Article Excerpt: The formula for distance traveled between frames would be : Feet Traveled = (MilePerHour * (5280 ft/Mile) / (3600 s/Minute)) * photo_interval
The citation images below were all found to have a photo interval of 0.363 seconds between frames according to the timestamps on the images. Our first citation stated the vehicle was traveling at 56 mph.
Example 1: Image #1 Example 1: Image #2
That works out to 56 *5280/3600 * 0.363 = 29.18 feet. By superimposing the vehicle from the second image over the first, you can see the distance traveled:
Example 1: Both Images
The length of this pickup is about 16 feet, meaning the truck should have traveled 1.82 truck-lengths (or one length, plus another 13.18 feet) to move at this speed. We’ve added guidelines to compare the image, showing that the distance is one length, plus the gap between the front and back of the two truck images. That gap is much less than half a truck-length. We estimate this to be less than four feet based on the size of the wheel-wells. That would work out to a total distance of less than 20 feet, which given the interval of 0.363s would be just under 38 mph. This indicates an error of 18 mph, and a speed 9 mph below the threshold for issuing speed camera tickets under state law (47 mph in this case).
Our second example is even more obvious. This truck was measured by the device to be traveling 65 mph on July 28, 2010.
Example 2: Image#1 Example 2: Image#2
As such should have traveled 34.6 feet, which given this vehicle’s length of no more than 16 feet it should have traveled at least 2.1 truck-lengths. Superimposing those two images, you can see that this distance is not even close that distance.
Example 2: Both Images
In fact, the front of the vehicle in the first image is almost perfectly lined up with the back of the truck in the second frame, meaning the vehicle only traveled about 16 feet. That gives us a vehicle speed of: 16ft/0.363s)*(3600s/hr)/(5280ft/mi) = 29.88 mph.
It would seem that even driving 5 mph below the speed limit might not get you past these speed cameras without a fine. Another example, which took place on September 9, 2010, showed a van clocked at 51 mph and therefore should have traveled 27.15 feet between images.
Example 3: Both Images
This van is about 17 feet long so it should have traveled 10 feet longer than one length based on the recorded speed. As you can see, the front of the first superimposed van image is almost aligned with the back of the second van image. The van couldn’t have traveled more than one or two feet more than one van-length, placing its speed right around 35 mph a difference of close to 16 mph compared to the recorded speed.
Opt traffic told The Washington Post that the company’s cameras “accurately measure vehicle speed within .5 mph below speeds of 55 miles per hour.” Well if they said that it must be true, right?
Example 4: Both Images
But the most compelling image is this one, dated July 22, 2010, showing both an Auto Value truck and a Metro bus. The citation charged this pickup truck with traveling 76 mph. The 0.363 photo-interval means the vehicle should have traveled 40.46 feet which is more than 2.5 truck-lengths. The superimposed images clearly show the actual distance to be a little more than one truck length, less than 20 feet total—not even half the distance it should have traveled at 76 mph. (We note that the bus in the right lane traveled a bit over half its length, and this would also have been well under 40.46 feet. So while one could consider whether this one was possibly a matter of incorrect lane assignment, even if that were the case the bus was also traveling much less than 76 mph.) Mr. Foreman hung this last photo in his shop for some time to protest what he called the “Indian Head Highway Robbery.”
We have received many other examples of this from other drivers in the area. The amount of the discrepancy varied from case to case but one thing is clear: the speed cameras in Forest Heights are not consistently producing accurate speed measurements. While the majority of documented cases occurred in the summer of 2010, some questionable photos were dated in December, meaning that whatever issue caused these errors it is likely still there.
Mr. Foreman’s business was adversely affected by what they now refer to as the Forest Heights Toll Plaza. When the tickets first started to arrive he took the matter up with his employees and warned them about speeding, holding them responsible for paying the tickets. However even though the drivers all knew about the camera locations, the tickets kept coming. When he learned that the vehicles had in fact not been traveling the speeds they were cited for he realized he had been disciplining employees for something which was beyond their control. That is not a good position for an employer to find himself in. Some members of his staff who need to do deliveries now drive far out of their way to avoid the “Forest Heights Toll Plaza” even though this costs the business time and money.
Similar cameras are used in many other municipalities in Prince George’s County, including College Park, Riverdale Park, New Carrollton, Berwynn Heights, and Mount Rainier. There have been specific reports of errors from these cameras documented in Brentwood, Riverdale Park, and Cheverly.
When a similar situation was investigated in Cheverly, the response from the company was that the vehicles had simply decelerated between the time the speed measurement was taken and the time the photos were taken. There are three problems with this. First, in the above photos, the vehicles do not appear to have their brake lights on. Second, the vehicles simply did not have enough time. A typical deceleration rate for a car or light truck is around 25 feet per second per second. Looking at our last example, decelerating from 76 mph (111 fps) to 35 mph (51fps) would take 2.4 seconds. The vehicle would have traveled about 194 feet, or twelve truck lengths, in that amount of time. The actual distance between the camera and the photo position is only a small fraction of that distance. Lastly, Optotraffic’s own documents state that citation images can be used for speed verification: “While the primary evidence for issuing a speeding citation is the calibrated Lane Sensor, the two photos provide the secondary evidence of speeding that is presented to the citation recipient. Since a stationary object is present along with the vehicle, a photographic method also determines speed, guaranteeing fairness.”
But wait a minute, the machines are tested for accuracy: Doesn’t that mean they cannot possibly be wrong? According to the system spec of the similar Optotraffic cameras used in Brentwood: “Each Lane Sensor is third-party calibrated annually (by Maryland law) to verify the beam distance; in addition, the relative time between the sensors is calibrated daily using the 1 pulse-per-second (PPS) signals from the Global Positioning System (GPS) satellites” That sounds very impressive, but notice this only means they have calibrated the system’s components. The spec does not state whether the device is actually tested as a complete system under real world conditions. Whatever actual (unspecified) speed testing did take place, it seems unlikely that it was tested with thousands of vehicles of different configurations, sizes, two vehicles passing at the same time, etc. under a variety of conditions and confirming that none of their speeds were incorrectly measured. So at best, the devices were tested for “accuracy” under “controlled conditions,” but not for consistent accuracy under real world conditions. Just because a device works correctly sometimes under perfect conditions does not mean it works right every time under all conditions.
Likewise, the device “has a test mode that runs daily to verify the basic functionality of the data processing unit and calibration of the Lane Sensor.” A sample output is shown at right.
If it is tested every day then it must be accurate, right? But wait a minute, how could an automatic test possibly be checking the accuracy of speed measurement against a real moving vehicle of known speed? Did they arrange for one to automatically drive past at precisely 35 mph the same time every day? Unlikely. The answer is that it is not. It is merely testing that it has a GPS signal and that various components are “working.” The chart showing the “speed error” may seem very technical and is made to appear like meaningful testing is being presented as evidence in court, without an actual speed measurements on any vehicle being part of this self-test.
Laboratory tests or component tests may be over-simplifying what happens in the real world, the way the teacher of a first year physics class would simplify a problem for his students with massless frictionless pulleys, and falling bodies in a perfect vacuum. In the real world, the device needs to take many variables into consideration. If the lasers do not use the same point on the vehicle for both measurements the device may not calculate a correct speed, regardless of how accurate the individual components are or how often they are tested. Did both laser-sensors strike the same point? Was this an unusually shaped vehicle like a truck, a motorcycle, or an RV pulling a trailer? Could the device’s 32-foot telescoping pole start to sway or vibrate due to high winds or a passing truck, and would this effect the angle of the beams? Could something other than a vehicle interrupt a beam? And would any such problem be likely to present itself in a limited number of controlled tests?
So who is investigating what is going on? Only the town of Forest Heights and its contractor, who each have a substantial financial stake in finding that there is no problem.