Article: Maryland: Forest Heights Speed Camera Accuracy Questioned
The accuracy of the speed cameras deployed by Forest Heights on Indian Head Highway (State Highway 210) has been questioned by local residents were claiming innocent drivers were being ticketed. Citation photos appear to show many cases that speed cameras in Forest Heights cited vehicles for speeds far in excess of the speeds the citation images indicate.
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 hard (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 which always produced an incorrect result), any one specific person would be unlikely to get enough citations with extremely large errors in order 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 that 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.