The pandemic had already forced Brian Rose to cancel his wedding, close much of his business and keep his distance from family and friends.

He was home in Alexandria watching the news last weekend when images of crowds — sightseers, runners, amateur photographers, dog walkers, parents and their children — flooded the screen. Throngs of people had gathered at the Tidal Basin despite warnings from District and federal officials who banned group gatherings in an effort to slow the spread of the novel coronavirus.

As of Thursday, the tally of coronavirus cases surged past 1,200 in Maryland, Virginia and the District — a grim indicator of the continued spread of the virus and the increase in tests being administered to detect it. Dire warnings of how quickly and efficiently the virus can spread had clearly not gotten through to people, Rose thought. He decided to try a bit of levity.

Rose mounted a speaker to the roof of his 2009 Honda Civic, plugged in a microphone and hit the road.

At the Alexandria waterfront, he watched as lines of people crowded walkways and crosswalks.

“This is a public service announcement,” he said, his voice echoing from the speaker into the street. “Please practice social distancing.”

He drove through Old Town, up Interstate 395 and across the Potomac River. At the Wharf, Rose said, people clustered around seafood markets and restaurants serving takeout, many not standing six feet apart.

“Please stay home if you are able to,” he said. “This is a public service announcement. Please remember to stay safe during this pandemic.”

Inspired by the giant megaphone strapped to the roof of the Bluesmobile in the film “The Blues Brothers,” Rose said, he hoped the unusual sight might jolt people out of complacency.

Some pedestrians seemed to appreciate the effort, he said.

Joggers gave him a thumbs-up as they passed. Couples walking their dogs waved. Some people took out phones to capture pictures and video of the roving PSA-mobile.

But a lot of people, especially around the cherry blossoms that line the Tidal Basin, “just kind of looked at me weird,” he said.

“We are in a global pandemic,” Rose said, his voice carrying over the pink petals and green grass. “Please stay home to look at the cherry blossoms.”

Despite city officials shutting down streets, closing several Metro stations and all but begging people to stay home, legions of blossom-seekers walked past Rose’s car without a second glance.

Rose, 25, makes videos for a living. He filmed his outing and put it on YouTube, where, as of Thursday, it had been viewed more than 13,000 times.

For months, Rose had been envisioning this time in his life under very different circumstances. He was supposed to get married Saturday — a wedding that was eventually scrapped in favor of a small ceremony in his parents’ backyard. He and his wife streamed the nuptials to friends and relatives via Facebook.

Their honeymoon, he said, has been at home, under quarantine.

He occasionally leaves the house to deliver groceries to his parents and grandfather, from whom he keeps a distance of at least six feet, in line with recommendations from the Centers for Disease Control and Prevention.

“I’ve been worried for my family,” he said. “I’ve been trying to quarantine myself not only for my own health but for those that I’m close to. There’s a lot of anxiety right now; it’s an anxious time. So I’m doing what I can to stay positive through it all.”

When asked if he would go out and deliver more public health warnings from the front seat of his car, Rose laughed. If people are still gathering in groups, he said, why not?

“This was an outlet for me to get out of the house in a safe way by being sealed in the car and also being able to express some of the anxiety we’re all feeling right now,” Rose said. “If it makes people stop and think about what they’re doing, then maybe it will make a difference.”