(Ben Claassen III/For Express)

On Tuesday night, I experienced the most relaxed rush hour in Washington history. The only traffic? A single sport utility vehicle — or whatever you call those boats that crew teams use.

Otherwise, there was nothing to slow down my ride on Miss Sophie. The zippy 49-seater is the youngest vessel in the Potomac Riverboat Company fleet, and she was specially selected to ferry passengers on a new route between the Alexandria waterfront and the National Mall.

The company is already established in the water-taxi business with its regular trips between Alexandria and National Harbor, Md. (And it operates the Baseball Boat, which drops fans off right next to Nationals Park on game days, as well as a whole slate of sightseeing tours.) The addition of this Mall water-taxi service, which started April 4, represents another incremental step in the expansion of aquatic transportation in D.C.

It’s only a matter of time before Washingtonians, just like that guy in the new blockbuster “Noah,” take a look around and wonder whether they might be better off on a boat.

I came to that conclusion just before my 5:50 p.m. departure from Alexandria, as I strolled around the sunny dock, licked an ice cream cone and watched seagulls swoop across the sky. Not to knock Metro, but let’s just say that “glorious” is not a word that’s ever come to mind while waiting for a Red Line train.

When Miss Sophie pulled up, I handed over my one-way ticket — $14 — to first mate Hanna Thorsen and took a seat. Captain Steve Boulton walked over to confirm that I knew I was on the boat’s final run of the day. (There will be an 8:30 p.m. departure once the summer schedule starts on May 23.)

What I hadn’t realized was that I’d have the place to myself. It was just the three of us, so it felt like I got a private charter.

“See those silver domes?” Boulton pointed out. They’re part of the Blue Plains Advanced Wastewater Treatment Plant, which is the largest of its kind in the world. Thorsen recommended I check out the impressive view straight ahead, with the National War College looming in front of the U.S. Capitol. And then they both directed my attention to Bolling Air Force Base as we passed by its attractive waterfront housing. “The ones with the gazebos are for the higher-ups,” Thorsen noted.

For transportation nuts, the route offers some particularly impressive sights: planes taking off and landing, trains rumbling overhead across a bridge. But what I really liked was seeing all of the cars and tour buses looped around Hains Point — especially the fact that I wasn’t in any of them.

About 30 minutes after we left Alexandria, we glided up to a spot near the FDR Memorial, which greeted us with the pinkest of all of the trees in West Potomac Park (and a Capital Bikeshare station). As I stepped off of the boat, a family of four was getting ready to board.

“We’re going to have an adventure,” the parents promised their kids. And I bet it was a glorious one.