"I thought, I should take a photo of that," Holland said. "That would be cool to abstract that graphic."
He set out to find the bus again, and suddenly they were everywhere: tour buses from Poland, Italy and Spain with colorful, eye-catching designs.
Holland -- stunned to discover this mobile genre of art -- decided to photograph as many as he could. The project came as a natural extension of where his photography was going.
"I walk through the world with an imaginary frame in my mind's eye," said Holland, a graphic designer who is the professor of digital media at the Paris College of Art. "When people can't tell what (the image) is straight off the bat, that makes it more interesting to me."
His photographs are all shot from the same vantage point -- a close-up view of the graphic that fills the frame with a burst of color. After experimenting with different abstractions and solidifying his look, he began excluding things.
"One rule is that I don't have any typography in my shots," he said. "I'm not really thinking about where the wheel is. I'm not thinking anything except where the graphic is in relation to the frame."
By Holland's estimation, he's photographed about 1,200 buses. "It's astounding," he said. "Just in sheer volume." He rides his bike through the city, constantly searching for fresh designs.
"In an hour, I see 10 I haven't seen before," he said. "I see about 100 in any given outing. I never come up empty-handed."
The designs on the buses vary, their meaning often hidden. There is a bus with galloping teal horses, a bus with a blown-up image of George Washington, one with red palm trees, one with a dolphin diving out of a woman's hands.
"A lot of them are super weird, and that's what fascinates me," Holland said. "That's what keeps me going and interests me. Who did it and why?"
Though Holland has attempted to find the artists who use tour buses as a canvas, he's been unsuccessful.
"I can't figure out where it's all coming from," he said. "It feels like a free pallet for graphic designers to do whatever they want. It's interesting from a communications standpoint. It's interesting that they keep coming and they never stop."
Holland prefers to shoot the buses when they are parked, and on cloudy days to avoid glares and shadows. Most of the buses are found on streets around the Eiffel Tower and Paris opera house.
"I'll see a bus that's moving and I'll chase it," Holland said. "I've chased buses for miles and waited for them to park."
But for all the buses Holland has photographed, there are those that rushed by before they could be documented. "There are several that are in my head that I've seen that I've never found them again," he said.
Four years after photographing his first bus, Holland is putting together a book of about 250 images. But the search for new designs is ongoing.
"Every bus is different," Holland said. "The model of the bus changes. The panels are in different places." Sometimes, even the hubcap is painted.
"That's the moment where I'm like 'Oh god, that's art,' " he said. "Who took the time to put a gradient on a hubcap?"