Protesters shout anti-Nazi chants in Charlottesville in 2017. (Chip Somodevilla/Getty Images)

IT WAS preposterous for Metro to have considered using separate, dedicated subway cars for the array of racists, bigots, neo-Nazis, white nationalists and other thugs set to descend Sunday on Washington on the anniversary of the violence last year in Charlottesville. It may also have been an effort at sound policing.

That’s the paradox facing authorities in the national capital area as they prepare to deal with several hundred “protesters” expected for the Unite the Right rally downtown. In Charlottesville, official bungling enabled chaos, violence and, ultimately, a young woman’s death in the city’s streets. From a public-safety standpoint, one of the key lessons from that tragedy is the critical importance of separating mutually hostile demonstrators.

It’s one thing to ensure such separation above ground. But how to accomplish that underground in Metro, if racists and their antagonists, including Antifa counterprotesters, are crammed together aboard the same subway cars? Metro wisely scrapped the idea of separate cars, which was rejected by its biggest employee union, whose members are mainly African American and other minorities.

Now, the task for Metro, as for an array of local law enforcement agencies including D.C. police, U.S. Park Police, Virginia State Police, and Fairfax and Arlington counties police, is to keep the peace, allow for the exercise of First Amendment free speech rights and ensure that nothing resembling what happened in Charlottesville happens in the nation’s capital.

There is cause for guarded optimism. D.C. police and Metro transit police have a history of working cooperatively, including earlier this year when the two joined forces to combat a spate of robberies occurring above and below ground. D.C. police have also worked in the subway for major local events such as Major League Baseball’s All-Star Game last month and the March for Our Lives this spring.

Officials say that large contingents of extra security personnel will be deployed this weekend, including police in uniform and in plain clothes. They appear alert to the danger of physical confrontation, which serves no one’s interests except for the white nationalists, fringe figures for whom any manner of publicity only amplifies their twisted agenda.

That leaves the question of how to confront and counteract those who will converge downtown. In our pages a few days ago, Maria J. Stephan, who has written widely on nonviolence, described the variety of countertactics available to citizens who want to express outrage and opposition to bigotry and hatred without provoking or being provoked into scuffles and brawls.

Mocking them is a good approach, as is reaching for the wallet; in one town in Germany, Ms. Stephan noted, residents contributed 10 euros (about $11.40) to a program that induces people to leave far-right groups. She also recommends “dispersed, low-risk” techniques that avoid potential clashes while enabling a show of rejecting the bigots in the street. One example would be gathering on the rooftops of D.C. apartment buildings, hotels and businesses to shout for fundamental American ideals — tolerance, mutual respect, equal opportunity — that represent an affront to noxious groups such as Unite the Right without posing the risk of physical confrontation.