Here’s some Supreme Court caselaw for you. These cases I’m quoting are all good law. I’m not sure what cases you’re referring to when you say there are “judgments going in both directions.” None of those judgments could supersede the Supreme Court.

While capricious, random stops are not allowed, roadblock stops in general are fine according to the Court:

Accordingly, we hold that except in those situations in which there is at least articulable and reasonable suspicion that a motorist is unlicensed or that an automobile is not registered, or that either the vehicle or an occupant is otherwise subject to seizure for violation of law, stopping an automobile and detaining the driver in order to check his driver’s license and the registration of the automobile are unreasonable under the Fourth Amendment. This holding does not preclude the State of Delaware or other States from developing methods for spot checks that involve less intrusion or that do not involve the unconstrained exercise of discretion. Questioning of all oncoming traffic at roadblock-type stops is one possible alternative. We hold only that persons in automobiles on public roadways may not for that reason alone have their travel and privacy interfered with at the unbridled discretion of police officers. The judgment below is affirmed.

Delaware v. Prouse, 440 U.S. 648 (1979)

Suspicionless sobriety checkpoints are allowed under the Court’s holding in Michigan Department of State Police v. Sitz, 496 U.S. 444 (1990):

At traffic checkpoints the motorist can see that other vehicles are being stopped, he can see visible signs of the officers? authority, and he is much less likely to be frightened or annoyed by the intrusion . . . . Here, checkpoints are selected pursuant to the guidelines, and uniformed police officers stop every approaching vehicle. The intrusion resulting from the brief stop at the sobriety checkpoint is for constitutional purposes indistinguishable from the checkpoint stops we upheld in Martinez-Fuerte.

Martinez-Fuerte was a suspicionless border patrol checkpoints away-from-the-border case, in case you’re wondering

Suspicionless checkpoints for narcotics are NOT allowed, though roadblocks to capture a terrorist or dangerous criminal would be allowed, under City of Indianapolis v. Edmond, 531 U.S. 32 (2000):

The primary purpose of the Indianapolis narcotics checkpoints is in the end to advance “the general interest in crime control,” Prouse, 440 U.S., at 659, n. 18. We decline to suspend the usual requirement of individualized suspicion where the police seek to employ a checkpoint primarily for the ordinary enterprise of investigating crimes. We cannot sanction stops justified only by the generalized and ever-present possibility that interrogation and inspection may reveal that any given motorist has committed some crime.

Of course, there are circumstances that may justify a law enforcement checkpoint where the primary purpose would otherwise, but for some emergency, relate to ordinary crime control. For example, as the Court of Appeals noted, the Fourth Amendment would almost certainly permit an appropriately tailored roadblock set up to thwart an imminent terrorist attack or to catch a dangerous criminal who is likely to flee by way of a particular route. See 183 F.3d, at 662-663. The exigencies created by these scenarios are far removed from the circumstances under which authorities might simply stop cars as a matter of course to see if there just happens to be a felon leaving the jurisdiction. While we do not limit the purposes that may justify a checkpoint program to any rigid set of categories, we decline to approve a program whose primary purpose is ultimately indistinguishable from the general interest in crime control.

And a police checkpoint to ask motorists about a recent hit-and-run was upheld by the Court in Illinois v. Lidster, 540 U.S. 419 (2004):

We now consider the reasonableness of the checkpoint stop before us in light of the
factors just mentioned. We hold that the stop was constitutional.

The relevant public concern was grave. Police were investigating a crime that had
resulted in a human death. No one denies the police’s need to obtain more information at that
time. And the stop’s objective was to help find the perpetrator of a specific and known crime, not
of unknown crimes of a general sort. Cf. Edmond, supra, at 44, 121 S.Ct. 447.

The stop advanced this grave public concern to a significant degree. The police
appropriately tailored their checkpoint stops to fit important criminal investigatory needs. The
stops took place about one week after the hit-and-run accident, on the same highway near the
location of the accident, and at about the same time of night. And police used the stops to obtain
information from drivers, some of whom might well have been in the vicinity of the crime at the
time it occurred.

Most importantly, the stops interfered only minimally with liberty of the sort the Fourth
Amendment seeks to protect. Viewed objectively, each stop required only a brief wait in line-a
very few minutes at most. Contact with the police lasted only a few seconds. Police contact
consisted simply of a request for information and the distribution of a flyer. Cf. Martinez-Fuerte,
supra, at 546 (upholding inquiry as to motorists’ citizenship and immigration status); Sitz, supra,
at 447, 110 S.Ct. 2481 (upholding examination of all drivers for signs of intoxication). Viewed
subjectively, the contact provided little reason for anxiety or alarm. The police stopped all
vehicles systematically. And there is no allegation here that the police acted in a discriminatory
or otherwise unlawful manner while questioning motorists during stops.

For these reasons we conclude that the checkpoint stop was constitutional.

Fourth Amendment doctrine is one of my favs…