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Cross Examination of a Police Officer’s Visual Estimation

In the 2007 Fall / Winter edition of the Westchester County Bar Journal I wrote a detailed, lengthy, instructive article on how to cross examine and impeach a police officer’s visual estimation in a speeding trial. The framework of what you need to know is highlighted in this article.

Visual estimation of speed comes down to this basic algebraic equation: Rate x Time = Distance [R x T = D]. If you know any two of these variables you can easily and quickly calculate the remaining variable. Therefore, it is your job as counsel to elicit testimony of the length of time [T] of observation and the distance [D] the vehicle traveled over that length of time. Once you have that testimony you can then easily calculate rate of speed [R].

Once T and D are determined, simply divide D by T to calculate R. Mathematically, this is expressed as:

D ÷ T = R

However, R is obtained is in feet per second [FPS], not miles per hour [MPH]. To convert FPS into MPH you must divide FPS into the constant 1.466. This is the constant because at 1 mile an hour a vehicle is traveling 1.466 feet per second. Mathematically, MPH is expressed as:

R ÷ 1.466 = MPH

Below is a quick reference conversion chart:

88 60
44 30
132 90
66 45
22 15

In the 2007 article I went into detail on exactly how to elicit the testimony, how to impeach when the visual estimation was way off, and how to impeach even when the visual estimation was spot on. If you would like the full article feel free to e-mail me at

The author is the founder of and is licensed to practice law in New York, Connecticut and Vermont. He can be reached at 1-877-99-NO-TIX (1-877-996-6849) and handles speeding and traffic ticket defense cases anywhere in the aforementioned jurisdictions.