When a person fights a speeding ticket, the same basic principle of criminal defense apply: the prosecution must prove the case with evidence. Therefore, it makes sense that the best way to win a speeding ticket case is to knock out the evidence the ticket is based on.
Since most tickets are based on evidence gathered by radar or laser speed detection devices, the following will focus on the main challenges to these two types of evidence.
Recent and Reliable Calibration
Generally, radar and laser speed detection devices require regular calibration to ensure that the devices remain accurate. State traffic laws and rules of evidence will vary as to what is considered both recent enough of a calibration as well as how accurately they must be calibrated. In some jurisdictions, you may be able to make requests for documentation about the device's calibration history prior to the appearance date on your ticket, or at the first appearance in court. If you are not able to get the documentation regarding the device calibration, you may be left with having to question the officer on the stand to get that information.
You can ask the court to dismiss the case if the radar or laser speed detection device was not properly or recently calibrated, and depending on your jurisdiction, a court can dismiss the case for lack of reliable evidence. Frequently, officers are aware of which jurisdictions will dismiss for lack of calibration proof, and those officers will bring the calibration and testing logs for their speed detection devices to every hearing.
Officer Training to Use Device
Another area that you may be able to successfully challenge is the officers training to use the device. While this may seem like a hail Mary pass, occasionally, it happens that an officer does not get properly trained. Again, establishing improper training may not automatically equal a dismissal, as different jurisdictions handle matters differently, but it can.
This argument tends to be more plausible if you believe the officer pulled you over instead of another vehicle that was passing you at the time. If you establish the officer's training is insufficient in conjunction with a circumstance that shows the lack of training, a court can dismiss the case. You may want to investigate getting dash cam footage from the officer's vehicle prior to the hearing if you believe this to be the case.