Speed = distance / time.
This simple equation has been the backbone of The Baltimore Sun's determination that a series of city speed camera tickets have been erroneous.
That, two bricks, and a roll of yellow measuring tape.
The process works like this:
When trying to analyze the accuracy of a ticket, Sun colleague Scott Calvert and I first need to receive a copy of the citation. The city and vendor will not release copies of actual citations, so we rely on citizens to provide us with their copies. Once we have one in hand, we're in business.
Each citation comes with two pictures of how far a vehicle traveled over about half-a-second. Using the photos, we use landmarks, paint and other physical markings along the road to determine the spot of the vehicle in each picture. (As a rule, we are always overly generous to the camera when making these determinations.)
Then we wait for a break in traffic and run into the road. Once there, we mark the spots of the two photos with bricks, and then measure the distance traveled with the measuring tape. We always double-check the measurements, and fact-check each other's work.
Take the Subaru hatchback clocked going 56 mph on Cold Spring Lane on Oct. 5. If that were true, it would have traveled 41 feet in half a second. But we found it went just under 23 feet, translating to a speed of 31 mph — a hair over the 30 mph limit and not nearly fast enough to merit a $40 ticket.