Folks departing the fest (and likely the wonderful set by the Carolina Chocolate Drops) and then heading up Penn Avenue last night ran smack into the world premiere of Squonk’s latest. It’s a theatrically minded art-rock concert performed on the back of a flatbed truck.

I previewed the show for CP,  even sitting in on rehearsal, but it was hard to imagine how this one would turn out. The variables were many, from the logistics of setting up the portable stage to the outdoor acoustics and lighting.

The band must have started a little earlier than announced, but I caught the final half-hour of the 45-minute show. The stage was parked on a closed-off Penn, so that its backdrop was Downtown’s skyscrapers, and it stood shoulder-to-shoulder with the new subway stop.

It’s a competitive location, visually, and to be sure the stage looked a lot bigger when I saw it up close, during rehearsals at the Squonk farm.

And while the acoustics last night were good — new Squonk singer Anna Elder was in fine voice — volume was an issue. I was standing only a few rows of people from the edge of the staging area, and I could have used the music a little louder.

Still, the tunes were lush and lively, the choreography was funny, and a few of the stage bits came off really well. The floating-head blimp’s mouth opened and closed on cue (as though it were singing); the video projections looked good on the screen of spinning rotors; and Jackie Dempsey’s keyboard rotated on its horizontal axis, while she played it. The nicest acoustic surprise was how well the calliope mounted atop the truck’s cab sounded as played by Steve O’Hearn.

Squonk designed the show to travel, and it’ll be trucking to area performances all summer, starring with shows at Lawrenceville’s Arsenal Park, on July 12.

But you can catch GO Roadshow several more times at the arts festival, too, starting with shows today at 1, 4 and 9:45 p.m. There are two more Arts Fest shows on Sunday, at noon and 7:45 p.m.