MADRID — Jaime Colsa owns a transport company that delivers ordinary consumer goods — computers, food, drinks. The contents of his trucks aren’t eye-catching, but his vehicles certainly are, adorned with paintings showing cartoonlike faces, dogs, brightly colored geometric patterns, spirals and landscapes.

These trucks that crisscross Spain have been painted by artists as part of the Truck Art Project. Financed by Mr. Colsa, the project aims in part to bring street art back to its roots.

“Thanks to people like Banksy, this kind of art has made its way into the gallery,” Mr. Colsa, 45, said here recently. “But I thought it would be interesting and challenging to do the opposite — to get artists out of the gallery or the museum and actually back on the street.”