By requesting a contested hearing you are using your constitutional right to have the plaintiff (The State, County, or City) prove their case against you (the defendant).
This is similar to the trial process you may see on television. In many courts, a prosecutor will be at the contested hearing to present the case against you.
Generally the parties will be given an opportunity to make legal motions prior to the beginning of the case. Sometimes these motions relate to jurisdictional or evidentiary issues. For example, the defendant may make motions to dismiss the case based on jurisdictional or procedural errors. If the judge grants the defense motions the case would be dismissed. If not, the plaintiff will present a case against you, either by affidavit of the officer or through witness testimony. The defendant will be given an opportunity to cross examine the witnesses and at the end of the plaintiff’s case may make a motion to dismiss. If the judge does not grant the motion to dismiss the defendant is then allowed to present their case through witness testimony. Both sides are allowed to make a closing argument. The judge will then rule on the evidence and make a decision.
Under Washington State law, traffic infractions have been decriminalized. Therefore the burden of proof in traffic infraction cases is by a preponderance of the evidence (some use the term “more likely than not”) rather than “beyond a reasonable doubt”. In any case, the plaintiff is required to prove their case against you. You are not required to prove you have not committed the infraction unless and until the state proves by a preponderance of evidence that you have committed the infraction.
We always recommend that you obtain legal counsel if you are planning to fight your infraction at a contested hearing. Knowing the traffic laws, rules of evidence and rules of procedure greatly enhances your opportunity to protect your traffic record. In addition as many jurisdictions have prosecutors who prepare and present the case against you it only seems logical to have an attorney on your side. An experienced traffic attorney will understand your case, the rule of law, and be knowledgeable about the court you are appearing in.