|In Allegheny County,
Pennsylvania one can appeal the District Justice's order to the Common Pleas Court (County
Court). This really isn't an appeal, this is trial de novo (new trial) where the people of
the state are represented by a prosecutor. This is also a court of record; a
transcriptionist will record everything the participants of the trial say. The Common
Pleas Court is certainly "prime time justice" compared to the District Court.
Those charged with speeding will only get a censored version of this "prime time justice": Pennsylvania law does not allow these defendants to plead their case to the jury of their peers. Speeders must do with a Judge.
Our man prepared for his trial by researching literature about VASCAR and Pennsylvania law about speed enforcement.
VASCAR (Visual Average Speed Computer and Recorder) is really a stopwatch coupled with a calculator. Once a distance is entered, the operator pushes a button to start then stop the stopwatch. VASCAR displays the speed calculated from the distance entered and the time measured.
Thus, a VASCAR measurement depends on human input. Therefore, in order to make a VASCAR measurement as accurate as possible, the observer's/operator's reaction time must be as short as possible. (Reaction time is defined as "the time interval between an input signal (physiological) or a stimulus (psychophysiological) and the response elicited by the signal.)
What is considered "normal" human reaction time? First, let's take a look at the best: Drag racers. Average reaction time of (Top Fuel) drag racers at the 1997 U.S. Nationals was 0.124 ± 0.082 second. Imagine that our cop running VASCAR is a super cop, with drag racer like reaction times: What kind of error is introduced into the VASCAR speed measurement by a reaction time of 0.124 second? With the numbers testified to by our cop:
Distance _________________ = Measured Speed Real time ± Error 100 ____________ = 60.096 feet/second (40.97 mph) 1.54 + 0.124 or 100 ____________ = 70.621 feet/second (48.15 mph) 1.54 - 0.124
depending on whether the cop was 0.124 second too quick or too late.
The calculation above takes into consideration only one opportunity for error. However, the cop must not only start the VASCAR's stopwatch, but he also must stop it. Thus, he can introduce the error twice:
100 ____________ = 55.928 feet/second (38.13 mph) 1.54 + 0.248 or 100 ____________ = 77.399 feet/second (52.77 mph) 1.54 - 0.248
Looks like we are getting some error margin here: it is almost 15 mph. But wait a minute: the cop alleged that he clocked our man 66 mph (96.8 feet/second). If true, the elapsed time over 100 feet distance was 1.033 second. The error in speed reading introduced by human reaction time becomes even more severe:
100 _____________ = 78.064 feet/second (53.225 mph) 1.033 + 0.248 or 100 _____________ = 127.388 feet/second (86.855 mph) 1.033 - 0.248
WOW! An error margin of more than 33 mph! And remember, we assumed that the super cop in this example has reaction times similar to a drag racer!
Imagine if the cop is only human: Average adults show reaction times around 0.3 second -- it's not even worthwile to do the calculation. Obviously, we can no longer talk about accuracy and VASCAR in the same sentence. One can conclude that using VASCAR over a 100-foot distance cannot yield any accurate speed reading for the speeds alleged in our man's case. We come to this conclusion even before considering other sources of error, such as visual distortion introduced by the parallax effect.
(4) No person may be convicted upon evidence obtained through the use of devices authorized by paragraphs (2) and (3) unless the speed recorded is six or more miles per hour in excess of the legal speed limit. Furthermore, no person may be convicted upon evidence obtained through the use of devices authorized by paragraph (3) in an area where the legal speed limit is less than 55 miles per hour if the speed recorded is less than ten miles per hour in excess of the legal speed limit. This paragraph shall not apply to evidence obtained through the use of devices authorized by paragraph (3) within a school zone.
VASCAR is a device authorized by paragraph (3). Looks like even Pennsylvania lawmakers acknowledge that VASCAR is not a precise method for measuring speed.
Our man was pleased to find the section in red of the above paragraph: All he had to do to convince the judge that 100 feet in 1.54 second is not 66 mph but about 44 mph, with no error. The judge should dismiss the case. But will the judge listen? Although the math "problem" here is rather trivial, perhaps the judge will be more likely believe someone with a degree in math. Thus, our man enlisted the help of his friend, who is a CMU graduate with a degree in mathematics.
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