A study conducted jointly by the Texas and Pennsylvania Departments of Transportation concluded that the Clearview font increased the visibility distance for drives by 12% versus the existing Series E Modified font.
In 1994 the Federal Highway Administration determined that highway signs were no longer visible enough for a population that included older drivers. Over the next decade, the Clearview font was developed. Subsequently, the Texas and Pennsylvania DOTs conducted separate studies to see how effective the Clearview font was.
The full report on this font can be found at http://onlinepubs.trb.org/onlinepubs/trnews/trnews243RPO.pdf