WASHINGTON — The Supreme Court on Tuesday ruled that small population variations among a state’s Congressional districts do not run afoul of the principle of “one person, one vote,” even though advances in computer mapping technology have made it possible to achieve near-perfect equality in representation.
The court also added six cases to its docket for the coming term, including one concerning whether the police need a warrant to draw blood from someone arrested on suspicion of drunken driving who refuses to consent.
The ruling issued Tuesday, which was unanimous and unsigned, involved West Virginia’s three House districts. It reversed a divided decision from a three-judge panel of a federal court in Charleston, W.Va., that had rejected House districts with slightly varying populations. The Supreme Court blocked that decision in January, and it issued its ruling in time for the elections in November.
Tuesday’s ruling, like another unanimous decision from the justices in January concerning electoral maps in Texas, called for deference to judgments made by state legislators. West Virginia lawmakers had considered nine plans and had settled on one where the gap between the most populous and least populous districts was about 4,900 people, or 0.79 percent.
The Legislature rejected what it called the “Perfect Plan,” which contemplated a population difference of a single person.
“That appears, however,” Tuesday’s decision said, “to have been the only perfect aspect of the Perfect Plan.” The plan split counties, put the homes of two incumbents in the same district and moved a third of the state’s population from one district to another.
The plan the Legislature adopted did none of that, the decision said, and it “moved just one county, representing 1.5 percent of the state’s population, from one district to another.”
The decision, Tennant v. Jefferson County Commission, No. 11-1184, noted that the leading Supreme Court decision in this area, Karcher v. Daggett in 1983, had seemed to endorse a variance of 0.78 percent, which was almost the same as the one under review. Technological advances, Tuesday’s ruling said, altered neither the applicable legal standards nor how much dilution of the “one person, one vote” principle is tolerable.
The justices also agreed to decide a question that has divided the lower courts: When do the police need a warrant to obtain blood in a drunken-driving investigation?
The case arose from the arrest of Tyler G. McNeely, who was pulled over for speeding on a Missouri highway and exhibited, the State Supreme Court said, “the telltale signs of intoxication — bloodshot eyes, slurred speech and the smell of alcohol on his breath.” He performed poorly on a field sobriety test and was arrested.
Mr. McNeely refused to take a breath test or, after being taken to a hospital, to consent to a blood test. One was performed anyway, about 25 minutes after Mr. McNeely was pulled over, and it showed a blood alcohol level of 0.15 percent, almost twice the legal limit.
The state court suppressed the evidence, saying there had been no “exigent circumstances” that excused the failure to obtain a warrant. “Warrantless intrusions of the body are not to be undertaken lightly,” the court said in an unsigned opinion.
In 1966, in Schmerber v. California, the Supreme Court said no warrant was required to take blood without the driver’s consent after an accident where the driver and a passenger were injured. The fact that alcohol levels diminish over time figured in the court’s analysis, as did the time it took to investigate the scene of the accident and move the injured people to the hospital.
The question in the new case, Missouri v. McNeely, No. 11-1425, is whether the natural dissipation of blood alcohol by itself justifies taking blood without warrant in a routine case where, as the state court put it, “there was no accident to investigate and no injuries to attend to.”