Thursday’s ruling by the Fourth Circuit in United States v. Smith gives a bit more definition to the often hazy subject of the use of police roadblocks.

At 3:05 am on a March morning two years ago, Dennis D. Smith topped a rise on a Durham, N.C. road, and swallowed hard. He saw police lights, lots of them, just 300 yards away. Considering his felony record and the 9mm Ruger pistol on the seat beside him, Smith decided it would be best not to approach the police. He accordingly hit the brakes, turned abruptly into a long gravel driveway, and waited.

One of the officers manning the driver’s license checkpoint noticed Smith’s behavior, and drove over to investigate. He saw Smith’s car stopped about 240 feet from the road. As the officer approached the car, Smith slowly resumed driving, pulling his car another 120 feet around a curve in the driveway before reaching, unfortunately for him, a dead end. Cornered, he turned off his lights and waited. The officer predictably found him and, eventually, the handgun, which Smith had taken the precaution of throwing into the bushes.

In the subsequent federal prosecution for possession of a firearm by a convicted felon, Smith moved to suppress the evidence, contending that the officer did not have enough of a reasonable suspicion to warrant the traffic stop. The district court denied that motion and convicted Smith. Thursday, the court of appeals affirmed that ruling and the ensuing conviction.

Ironically, Smith was too clever for his own good. If he had simply turned into the driveway, backed out, and driven back in the direction he had come from, he would have the support of the court of appeals in his efforts to suppress the evidence. The court was careful to point out that there are perfectly innocuous reasons for drivers to do exactly that, such as a desire to avoid a traffic tieup due to a perceived accident. The court cited a Ninth Circuit decision with essentially those facts, and distinguished it by citing the pattern of suspicious behavior attributed to Smith.

At first blush, the court’s ruling may seem hard to reconcile with the initial proposition it cites, that “individuals have a right to avoid encounters with the police” (citing U.S. v Burton). But this panel crafted its reasoning based on Smith’s other actions, which it found inconsistent with innocently “going about one’s business.” The specific ruling of this case is that “when law enforcement officers observe conduct suggesting that a driver is attempting to evade a police roadblock — such as unsafe or erratic driving or behavior indicating the driver is trying to hide from officers — police may take that behavior into account in determining whether there is reasonable suspicion to stop the vehicle and investigate the situation further.”

Note that turning around and driving away from a roadblock still isn’t enough to justify a stop. But the court strongly hints here that a single additional factor will often be enough to justify a stop. If Smith had elected to simply turn around and drive away, he probably would have had to do so perfectly. One wonders whether a felon thus spooked by patrol car lights could have summoned the poise, and the driving ability, to do that.

The opinion will be useful for prosecutors and criminal defense lawyers, as well as those who handle civil rights cases involving, among other things, allegations of unlawful seizures based on arrest without probable cause. The discussion is essentially aprimer on how not to avoid a roadblock.