When discussing graffiti, it's helpful to address a few of the standard arguments in favor of it right away.

One is that graffiti is an art form. While that's true, it doesn't mean all graffiti is art. A name scrawled on a stop sign or utility box isn't art.

Some graffiti does indeed belong in a museum, especially works that have more visual interest, energy and sheer delight than a C-grade piece of murky Abstract Expressionism, many of which are enshrined in museums around the world. And artists like Britain's Banksy show how street art can break out of its urban context and make important statements. But Banksy's work isn't really graffiti.

What is graffiti is what covers the sound barriers and ramps on the new section of Interstate 35W just south of downtown Minneapolis. It's a blight and needs to be removed.

If we can agree that great street painting belongs in a museum, we can also agree where it does not belong. It does not belong on your garage, unless you put it there. It does not belong on private property without the owner's permission. And it doesn't belong on freeway sound barriers.

Cheap, low-effort tagging on the downtown on-ramps is vandalism. The best of the boastful typographical adornments are still vandalism. The longer it stays, the more graffiti appears. The end result — as anyone who's visited graffiti-indulgent cities knows — is the defacement of every possible space. Visual litter.

Think of New York City's subways in the 1970s and early '80s, every surface smeared with unintelligible scrawls. Or think of the great plazas and buildings of European cities defaced with hastily sprayed signatures.

I was in a California town a few weeks ago, and walked under an underpass that seemed a prime graffiti target. The walls had bright fresh paint that suggested something had recently been obliterated. Talking to locals, I learned that anything painted on the underpass was removed the next day. No matter how much time someone spent spray-painting their name, it was gone by rush hour.

Why don't we do that in the Twin Cities?

It's complicated, said Jeff Streeter, maintenance traffic services superintendent at the Minnesota Department of Transportation.

"If [the stretch of road] is still in construction, the construction companies are supposed to take care of it," he said. "Once it's turned back to us, graffiti is pretty low-priority. If we're getting lots of complaints, we get to it right away, but in the winter it's hard, because our employees also plow, and when they get back they have other work."

Streeter understands that graffiti is a concern for many Twin Cities residents, but says the department is challenged to address it.

"It's not like we don't want our cities to look good, but it's just lower-priority," he said.