These can be potential defenses to your case. All checkpoints must follow certain procedures. Ingersoll vs. Palmer is the key case that determined the proper procedures that must have occurred. It would be best for you to contact an attorney to assist you. Make sure you request a DMV hearing within 10 days of your arrest.
I have no idea why the previous answer is telling you to contact the DMV. You would need to do that if you were arrested for DUI, but since you indicate that you were not - that you were arrested for possession of drugs, then that piece of advice doesn't apply to your situation at all.
To answer your question, yes - the license checkpoints and/or seat belt checkpoints are considered "regulatory" or "safety" checkpoints just like DUI checkpoints. They must set them up properly, run them properly and insure minimal intrusion into your activities. Especially if this was specifically a driver's license and seatbelt checkpoint and you were in compliance with those. If those were readily ascertainable from the outset, more than a brief conversation with you seems a bit excessive.
Of course, during the contact, the officers have their "plain view" and could potentially justify a longer detention based on things they saw, heard, smelled, observed, etc. Whether or not they will be able to do so in your case will be determined by the police reports, records of the checkpoint and the timing of your stop and detention.
Given the complexity of this situation, you need a good criminal defense attorney to represent you.
Checkpoint stops are legal, but they have to adhere to certain guidelines in order to establish compliance. You need to speak to an experienced attorney in order to determine whether there are viable defenses for you.
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