The more critical of the two charges is the MJ charge, and how it was charged. If it was charged under 2C:35-10, the charge would be a DP (Disorderly Persons) offense. If it is charged this way, you may be eligible for a Conditional Discharge disposition, which for a first offense would probably be done without a plea. In esence, think probation (although it isn't) with drug testing. This is something you need to discuss with an experienced criminal defense lawyer before deciding what to do. The speeding ticket under most circumstances involves MV points and a fine, unless certain factual issues are present, which again you need to discuss with the lawyer. Whether you tell your parents is something you need to decide. Good luck.
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My colleague is correct that your biggest concern would be the marijuana charge. There is a recent case that the mere odor of marijuana is not necessarily grounds to search a vehicle. Not so sure that there is only the mere odor since you offered an admission. The facts of the case must be fully explored to determine if there is an argument that the search was valid.
Your facts don't clarify whether you were charged with a motor vehicle summons for having marijuana in your vehicle which, if convicted, would result in a 2 year loss of license. Frequently (no guarantee) a prosecutor will be willing to dismiss that summons if you get a Conditional Discharge as was explained by Mr. Bailey.
By all means, don't go at this alone. Mom and Dad may be more understanding than you think, they are likely not completely surprised that you have smoked marijuana and the consequences involved are quite serious.
So as not to sound foolish, I should clarify that you can (and usually are) charged with both possession of marijuana (a criminal offense) and possession of cds in a motor vehicle (a traffic offense). Sounds like the same charge but they are treated differently with different consequences.