We're not talking about toll booths, we're talking about sobriety checkpoints. I have been through checkpoints. In fact, the last checkpoint I went through, I was pulled off the road and had my vehicle searched because I didn't put the renewal sticker on tags when it was raining. I had the sticker in the car and presented it with the proper registration renewal document. So, yeah, my car was searched, no one asked me if they could search it, and it would never have happened if it weren't for that "sobriety checkpoint". Oh, by the way, I got a warning ticket for expired registration. I wasn't doing anything wrong. AND it was raining that night, too, so the officer told me to put the sticker on sometime when the weather was better.
Aren't they searching you, though? They have you stopped and they look inside your vehicle. They are searching for signs of alcohol usage. And they do it when you haven't done anything to cause them to stop you. I understand the good intentions behind it, I just don't understand how its legal.