Flickr user Greg Matthews (gregpm) said he shot this photo at a sobriety checkpoint in checkpoint in Riverside, Calif., in 2011 Flickr user gregpm—Creative Commons

Just about a mile from the town line with Concord, drivers on Route 4 in Chichester Saturday night reached a police roadblock where they were stopped and asked to show their license and registration.

Unlike normal traffic stops, these drivers didn’t have to do anything wrong to get pulled over. A judge granted a court order giving officers – some from state police, some from local departments – the authority to stop anyone approaching the road block to assess their sobriety.

While the results of Saturday night’s sobriety checkpoint aren’t yet known, if it was a statistically average night, about 235 drivers were momentarily detained by officers, with flashlights and breathalizers at hand. One or two might have been arrested and charged with driving while intoxicated, according to the averages of 10 years of state police data.

But drunk drivers likely were not the only people arrested. On average, sobriety checkpoints result in just as many arrests for crimes unrelated to drivers’ blood-alcohol content, such as driving without a valid license or possession of drugs, according to a review of police reports from two years of sobriety checkpoints.

Roadblocks set to detect crime in general would violate the Fourth Amendment, which protects against unreasonable search and seizure. But the Supreme Court made an exception for sobriety checkpoints – permitting stops without probable cause – because it determined the public safety interest in curbing drunken driving outweighed the intrusion on law-abiding drivers.

The recent evidence that sobriety checkpoints frequently result in arrests unrelated to drunken driving, however, could expose the law to a challenge, legal experts said.

“If the purpose of the roadblock is to see if we can catch people committing any number of crimes, that would be declared unconstitutional,” said Buzz Scherr, a law professor at the University of New Hampshire. “They could try to make the argument that it’s a subterfuge, that the DWI roadblock is a pretext to catch people for other things.”

Unrelated arrests

In requesting a court order for the Chichester checkpoint, state police Staff Sgt. Charles Johnston noted that the number of fatal car crashes statewide – and the proportion related to alcohol consumption – have “remained relatively constant each year” despite efforts to educate drivers and prosecute offenders. Johnston said sobriety checkpoints are a tool to help curb that dangerous behavior.

In fact, there were slightly more fatal crashes in New Hampshire last year than any other year since 2005, according to data Johnston submitted to the judge. The proportion of those 130 fatal crashes that were related to alcohol – 56 percent – is in line with recent years, and it’s significantly higher than the average during the 2000s.

From 2003 to 2010, about 35 percent of all fatal crashes were alcohol-related, according to Johnston’s affidavit. From 2011 on, that number has increased to nearly 57 percent, showing that the majority of fatal crashes in New Hampshire now involve alcohol.

To combat that trend, Johnston wrote that the state police conducted 15 sobriety checkpoints last year, stopping 2,574 vehicles and arresting 21 people for driving while intoxicated.

But a review of police reports shows that those DWI arrests comprised less than half of the total arrests made at checkpoints last year. Of the 61 people arrested, 29 of them were charged with driving while intoxicated.

The year before, according to police reports, 90 people were arrested at sobriety checkpoints, 44 of whom were charged with driving while intoxicated.

In an acute example, state police stopped 149 vehicles at a Saturday night checkpoint in Bow in 2015 and arrested four people. One person was accused of driving while intoxicated, while two others were charged with drug possession and one was taken in on a warrant for criminal mischief.

The following year, when police applied for another checkpoint in the same spot – the intersection of Interstate 93, Route 3A and Hall Street – it was granted again. This time they stopped 192 cars and arrested two people for drug possession.

On average, police stopped 150 cars at checkpoints in order to make one DWI arrest.

In response to a Monitor right-to-know request last summer, state police Capt. Matthew Shapiro said no Superior Courts judge denied any of his agency’s requests for a sobriety checkpoint in the prior year.

‘Low arrest numbers’

Over the past 10 years, more than 85,000 people have passed through a sobriety checkpoint in New Hampshire, according to state police data.

The share of operators accused of drunken driving hasn’t exceeded 1 percent of the total traffic stops since 2006. In 2010, when state police checked 14,226 vehicles – more than any other year – 52 people were accused of driving while intoxicated, or 0.37 percent.

But rather than pointing to the scarcity of arrests as evidence that sobriety checkpoints don’t work, the state Supreme Court suggested an alternate theory in a 2007 case, State v. Hunt.

“Of course, low arrest numbers may demonstrate the relative ineffectiveness of sobriety checkpoints for the detection of drunk drivers, but such numbers may also demonstrate effective deterrence,” Chief Justice John Broderick wrote, declining to rule that the checkpoints violate the state constitution.

Behzad Mirhashem, a law professor at UNH, questioned if that line of thinking could ever result in an opinion that sobriety checkpoints aren’t effective enough to warrant the privacy intrusion.

“So, checkpoints are unconstitutional if one shows not only that they result in few arrests, but that they have no significant deterrent value. Practically speaking, how would one make such a showing?” he asked.

Broderick also noted that the U.S. Supreme Court also held that sobriety checkpoints don’t violate the Fourth Amendment.

Change over time

There are cases, however, in which a preponderance of evidence has resulted in a change of opinion on the U.S. Supreme Court.

“One of the reasons why a court might revisit a decision is if empirical information comes in that demonstrates the rule isn’t really working in the way that the court thought it would,” said John Greabe, a constitutional law professor at UNH.

The most famous example of that is one of the most well known Supreme Court cases in history, Brown v. Board of Education, which overturned the “separate but equal” doctrine established by the earlier Plessy v. Ferguson.

“They said the evidence in Plessy was decided in 1896, it’s now 58 years later, and what we’ve learned is that separate is inherently unequal,” Greabe said.

Scherr said that someone who’s charged with a crime unrelated to drunken driving could theoretically challenge sobriety checkpoints’ constitutionality by saying the reality hasn’t measured up to what the court expected.

“If there’s a return on every DUI roadblock of less than 1 percent, is that effective? Is that the least intrusive means to accomplish their goal, as opposed to doing what they already do (on patrol)?” he asked.

He also noted that the number of people who are arrested for crimes unrelated to drunken driving might show that sobriety checkpoints are less efficient and more intrusive than the courts anticipated.

“You’d have to do a lot of data collection,” Scherr said. “I don’t know what the numbers would be to make it significant.”

(Nick Reid can be reached at 369-3325, nreid@cmonitor.com or on Twitter at @NickBReid.)