In NJ they announce the checkpoints ahead of time in local newspapers. This is (presumably) to avoid breaching the 4th amendment.[1] Otherwise police would have

In NJ they announce the checkpoints ahead of time in local newspapers. This is (presumably) to avoid breaching the 4th amendment.[1] Otherwise police would have to establish reasonable cause to pull a car over. Or at least that's what a shitload of case law looks like (they had a window obstruction or were driving 'erratically', for instance) [1] https://en.wikipedia.org/wiki/Michigan_Department_of_State_Police_v._Sitz https://en.wikipedia.org/wiki/Michigan_Department_of_State_P...