The idea seems reasonable enough. Because the Three Sisters Bridges across the Allegheny River are about to undergo extensive renovations, why not ask the public what colors the bridges should be painted?

The suggestion to paint the three (located at Sixth, Seventh and Ninth streets) came from a call-in show with Allegheny County Executive Rich Fitzgerald. A caller said we should paint the Rachel Carson Bridge green and the Warhol Bridge silver. Fitzgerald and Mayor Peduto ran with the idea. They set up a survey on the web and gave participants four options, which also included repainting them their current color of yellow. A press release has encouraged participants to vote.

This is hardly Pittsburgh's most pressing issue, but it's crucial that we get it right. Thus far, though, no vocal public figure has. Painting the bridges is a matter of procedure as much as actual color. Because federal funds will support a large portion of the renovations, we are obligated to undergo the National Historic Preservation Act's obscurely named Section 106 process, which follows the same guidelines as are used for the National Register. Bill Callahan, Western Pennsylvania community-preservation coordinator in the state Bureau of Historic Preservation, explains that his bureau will determine whether the proposed renovations fit the character of the historic structures. PennDOT will then have the obligation to "avoid, minimize or mitigate any adverse effect."

Under the Section 106 process, there is an opportunity for public input, but it comes only at a point in the process at which historically suitable proposals for the given structures have been proposed. Opening this to a vote as a first step — even a non-binding one — before understanding what our historic precedents and possibilities are is a substantial procedural blunder.

It negates the considerable achievement of placing such things on the National Register, and it diminishes our sense of obligation to historic-preservation rules and guidelines, which are already much less powerful than most people realize. Pittsburgh cannot claim to value its historic structures if it takes this renovation project, with its established rules for preservation, and runs roughshod over them.

Painting something green to honor the environmental legacy of Rachel Carson is like listening to a ten-dollar bill to honor the musical achievements of Johnny Cash. More importantly, it clearly runs counter to the original intentions of the designers of the bridges. They placed a priority on identical appearance of the three structures, and they didn't remotely consider outlandish colors (though thematic Aztec Gold, which has been in popular use in recent years, might yet be the subject of debate). "At minimum," says Callahan, "they should be identical."

There might yet be disagreement on the degree to which changing paint colors is allowed on historic bridges. As an architectural historian with a Ph.D. and some specialized research in early-20th-century bridges here and in New York (where debates preceded the practices in Pittsburgh), I will argue that consistent and suitable colors are crucial to the bridges' historic character. Research is not yet even clear on what the exact color was originally. It would be instructive and arguably necessary to do what architect Roxanne Sherbeck suggested on social media: Do historic paint analysis to determine the bridges' original colors more definitively. It matters most that we identify them with historical accuracy and appropriate process.

I would also argue that we should make the bridges city historic monuments, which would place them under closer scrutiny and tighter city control. They are already nationally recognized. Why haven't we done this already? It would (or at least should) put the question of color into the purview of the Historic Review Commission (and then city council), under whose guidance there would still be opportunity for public comment.

Neither type of listing, national or city, offers complete protection for a structure's historic character or authenticity. Under current laws, PennDOT has too much sway in the final actions. All the more reason why we should treat them as historic assets from the start, not as subjects for some sort of popularity contest.