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


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.

IMPORTANT NOTICE: The Answer(s) provided above are for general information only. The attorney providing the answer was not serving as the attorney for the person submitting the question or in any attorney-client relationship with such person. Laws may vary from state to state, and sometimes change. Tiny variations in the facts, or a fact not set forth in a question, often can change a legal outcome or an attorney's conclusion. Although has verified the attorney was admitted to practice law in at least one jurisdiction, he or she may not be authorized to practice law in the jurisdiction referred to in the question, nor is he or she necessarily experienced in the area of the law involved. Unlike the information in the Answer(s) above, upon which you should NOT rely, for personal advice you can rely upon we suggest you retain an attorney to represent you.