Can I present my vehicle’s gps data to contest a speeding ticket.

The officer wrote on the citation and quoted to me he clocked me at 83mph in a 65 zone. He wrote the ticket for 70mph. My vehicle’s gps system takes a reading every 5 seconds. The data shows my maximum speed prior to the officer stopping me to be 69.5mph with an average speed of 66.15mph over the prior 8 mi stretch of highway. The data is time and position stamped, which matches the ticket time and position. Do I have a case and how would the evidence be presented.

Asked on October 7, 2017 under General Practice, California

Answers:

SJZ, Member, New York Bar / FreeAdvice Contributing Attorney

Answered 3 years ago | Contributor

YOU cannot present the evidence, because you cannot authenticate it, unless perhaps you are in fact an engineer with the correct training and experience to explain how the GPS works, to testify credibly that you checked it and validated that it was accurate, that have been able to confirm the data was not tampered with, etc. (And even if you are such an engineer, because you have a personal stake in the outcomes, your testimony on these topics will be subject to challenge on the basis of your motivation; it will be less persuasive than an impartial expert's testimony.) What you would need to do to present this testimony in court is to hire the appropriate engineer or computer science expert--e.g. someone who has worked on such systems--to test your GPS, validate its data, and present it in court; otherwise, without an expert providing a reason for the court to trust and accept it, the court will not entertain it. But hiring such an expert maybe expensive; it is not clear that it would be worthwhile doing so.


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