The Infrastructurist sums up the research behind the change to federal policies about road sign lettering. Road signs in coming years will need to be changed to move away from all CAPS in order to improve readability, particularly at night:

The shift reflects years of research into how drivers—particularly the elderly—react to road signs. In the late 1990s researchers at Penn State’s Pennsylvania Transportation Institute compared traditional highway signs to those with mixed-case Clearview lettering. They sat people age 65 to 83 in the front seat of a Ford Probe and approached a sign until the person could read it, repeating the tests with various fonts in both daytime and night.

The results, as the name Clearview suggests, were clear. Mixed-font Clearview was readable from roughly 440 feet away, whereas typical all-cap lettering was readable only at a distance of 384 feet. By expanding the interior spaces of certain letters, Clearview also reduced halanation—the process by which letters blur together late at night. In darkness Clearview became readable at 387 feet, against 331 for the standard highway font style.

All told the researchers found a 16 percent increase in readability with Clearview. On a typical 55 m.p.h. highway this translates into “two more seconds to read and respond to a sign,” they concluded in a 1998 report.

While this will cost money in the short term, it should lead to an improved driving experience. But it is also interesting how an issue like this can become fodder for political debates about how much money the government should be spending.