Speeding ticket evidence: how to use your GPS data
Last updated 5 August 2026
Most drivers who believe a speeding ticket is wrong have nothing to show for it. By the time the citation arrives, the drive is a memory, and a memory does not stand up against a radar reading. A continuous GPS log of the drive changes that: it is a record made at the time, not a recollection made afterwards.
This guide explains what makes a speed log useful as evidence, what it cannot do, and how to put a report together if you decide to contest a ticket.
What makes GPS speed evidence credible
A screenshot of a speedometer proves nothing. What a court or prosecutor can work with is a record with these properties:
- Continuous. Recorded across the whole journey, not started when you saw the patrol car. A log that begins moments before the alleged offence invites the obvious question.
- Timestamped. Every reading carries its own date and time so it can be lined up against the time on the citation.
- Honest about accuracy. GPS is not perfect. A log that reports the accuracy of each fix — and discards the readings that were too weak to rely on — is far more persuasive than one that silently presents every number as fact.
- Unedited. Exported as a single report you did not retype or adjust.
How accurate is GPS speed, really
Satellite positioning measures speed from the Doppler shift of the satellite signals, not by dividing distance by time, which makes it more precise than most people assume. With a clear view of the sky, speed is usually accurate to within roughly 1 km/h.
Accuracy falls apart in predictable places: tunnels, multi-storey car parks, streets lined with tall buildings, and dense tree cover. Those conditions produce readings that can be wildly wrong for a few seconds. This is exactly why the accuracy figure matters — a well-built log flags the weak readings instead of averaging them into the result, and an opposing expert who spots unflagged noise in your data will use it to dismiss the whole record.
What a useful report contains
When you export a drive from SpeedProof, the PDF report includes:
- The date, start and end time, and total duration of the drive.
- Highest and lowest recorded speed, with the moment each occurred.
- A map of the route actually driven.
- An accuracy timeline showing which stretches were recorded under strong GPS and which readings were discarded for being below the accuracy threshold.
- The underlying reading-by-reading data table.
The discarded readings are printed rather than hidden. It is counter-intuitive, but publishing your own weak data is what signals the rest of it was not cherry-picked.
If you decide to contest a ticket
- Read the citation carefully and note the exact time, location and recorded speed the officer alleges.
- Find the matching drive in your history and check that your log actually covers that time and place. If it does not, or if it agrees with the officer, contesting is likely a waste of your time.
- Export the drive as a PDF report and keep the original file — do not edit it or paste figures into a document of your own.
- Check the deadline on the citation. In most places, missing it forfeits your right to challenge regardless of what your evidence shows.
- Submit the report with your written statement, or take it to your hearing along with any other evidence such as dashcam footage.
What GPS evidence cannot do
Be realistic about the limits. A GPS log records your speed; it does not prove the officer’s equipment was faulty, and in many jurisdictions a properly calibrated radar or laser reading is given significant weight. Your log is strong when it shows a consistent, plausible speed across a stretch of road that contradicts a single reading — it is weak when it depends on one or two isolated data points.
It also will not help if you were, in fact, speeding. The honest use of a speed recorder is to know what happened, which sometimes means learning that the ticket was right.
This guide is general information about how speed data is used, not legal advice. Traffic law differs by country and by state, and the weight given to any evidence is for the court to decide. Consult a qualified lawyer in your jurisdiction about your specific case.
Start recording before you need it
Evidence only exists if it was recorded at the time. SpeedProof runs in the background and can start automatically as soon as the car begins moving, so the log is already there if a drive is ever questioned.