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I am sorry to hear about this situation. Assuming he wants to plea not guilty - which is indeed recommended - he would show up at the first hearing and do so. If this is the first hearing - and I understand it is - then all the Court will want is his plea.
Once that is done, then the case will be reset for a few weeks or month out, for a trial date. This will give time for your son and the prosecutor to negotiate.
If this case gets to trial, the prosecutor is likely to call the officer who will make an appearance and explain what he feels happened. He may or may not bring his dashboard camera tape that can also show what happened, if there is one. Normally, the Judge (or Jury, if he has a jury trial) takes the word of an officer over the Defendant.
The prosecutor is normally very backed up. They are handling literally dozens of cases at once. Setting a matter for trial - jury trial, more so - is a serious issue since they have little time to prepare, file the proper motions, and generally make room for the trial to happen.
Very often, individuals in his situation are given a "plea deal," if they have little/no traffic record. Individuals in his situation are very likely to be offered two possibilities:
1. Deferred prosecution (which dismisses the charge if he simply is not charged/convicted of anything else in 6 months to a year, but, pay court costs); or
2. Traffic school (although some Courts do not have this as an option and this may not be an option here unless the prosecutor agrees to lower the charges).
One can always ask for even a more favorable plea deal, including a "non-moving" violation, that would be less of a fine and not count as points. If the prosecutor agrees, then this is often considered a good deal.
Negotiating with the prosecutor for a deferment and/or reduced plea deal after pleading not guilty and setting it for a jury trial is normally a good way to use one's leverage. Of course, if this does not work, one's other option is to indeed set it for trial. Doing so may have the prosecutor reexamine their offer to him. Using counsel throughout all this is recommended - the prosecutor is likely to take the threat of trial more seriously if an attorney is already involved.
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