The city council in Ames, Iowa, just wanted to honor LGBTQ people during the local Pridefest. What the officials of the college town got instead was national attention and a showdown with the federal government.

The trouble started with the city’s decision to repaint the crosswalks at a downtown intersection, using the patterns of the rainbow flag and transgender pride flag. The new designs evidently caught the eye of someone at the local Federal Highway Administration building two blocks away, because the agency soon sent a letter pushing the city to reconsider.

Federal engineers have long been sticklers for safety rules that call for roadway features to be consistent across the country. They want the crosswalks in Ames, Iowa, to look just like the crosswalks in Ames, Texas, and like those in Franklin, Texas, and Franklin, Maine. The rainbow bands the Iowa town put down looked nothing like the black-and-white zebra stripes mandated by national standards. So the highway agency sent Ames officials a letter warning them that the crosswalks did not comply with federal guidelines.

The city council ignored the warning and has kept the colorful crosswalks in place. “I don’t think they have jurisdiction over the roads in Ames,” city attorney Mark Lambert says. “These are streets purely paid for by city funds. I don’t think they can punish us in any way.”

That open defiance of the federal government has struck a nerve far from Ames. City officials, public artists, and the highway honchos have spent years in a nationwide battle over artistic crosswalks. Rainbow patterns can be spotted in San Francisco and Atlanta, as well as Ames. Baltimore has crosswalks that look like zippers. Piano keys connect the curbs near the Eastman School of Music in Rochester, New York. A checkerboard flag lies near the Nascar Hall of Fame in Charlotte, North Carolina. The highway agency has repeatedly warned city officials against such treatments but hasn’t resorted to wielding its mightiest weapon: withholding the federal funds that states and localities often use to keep their roads in shape.

The debate has intensified as pedestrian deaths nationally have jumped by more than 50 percent in the past decade, to more than 6,000 in 2018. Experts have blamed the increase on factors including the proliferation of smartphones that distract both drivers and pedestrians, the popularity of ever-bigger SUVs, and road design that encourages speeding. That’s one reason pedestrian infrastructure has entered the spotlight. For all the benefits of civic pride and creativity that reimagined crosswalks may provide, the question for the engineers who control the streets is whether they improve or impair safety.

One reason for the confusion is that few studies have looked at how drivers react to novel crosswalk designs. Even some that have been done are inconclusive. Oklahoma transportation engineers, for example, studied the effects of a crosswalk painted to appear in 3D, meant to improve safety at a crossing near a school. The design gave drivers the illusion that the stripes were actually raised blocks. The engineers found that many motorists did slow down when they saw the markings, at least at first. But they also found that a significant number of motorists swerved to avoid them, replacing one dangerous behavior with another. “Additional study is needed to determine if installing a 3D crosswalk diminishes or enhances pedestrian safety,” the researchers concluded in 2018.

If we don’t try things, how do we know if there’s any value in it? Pam Fischer, a traffic safety consultant

Very few states or cities have gone through the long, formal process of getting federal approval for their new designs. That’s largely because the process is designed to test new technologies or designs that can then be used across the country, not for one-off projects that individual cities use to add a touch of whimsy. It calls for rigorous, scientific experiments, and by its very nature can address only one kind of new crosswalk marking at a time. Maybe 3D blocks are dangerous but rainbow patterns are even safer than the standard zebra stripes, or zippers are bad but buttons are good. The only way to know is to test each individually.