If the goal is to defeat the charge, then your son needs a lawyer. The case is probably one of the easier to win, because it will be one citizen's against another, and that does not usually equate to proof beyond all reasonable doubt. However, without a lawyer to cross examine the witness at trial, the judge could decide to do what traffic judges usually do: find the driver guilty no matter what the facts may be.
Hiring a lawyer frequently causes the judge to treat the case with more objectivity, if only because the judge knows that you're shelling out money for the lawyer, so that operates as punishment even if the judge finds the defendant not guilty.
For a traffic defense lawyer referral, see this link
Hope this helps..
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