The E-road network is designated by UNECE, not the European Union. It’s an entirely different body that even includes Canada and the U.S. for some reason.
Various UN commissions and congresses have designated similar networks all over the world. The E-road network overlaps somewhat with another UN-designated network, the Asian Highway. Most of these networks already have well-established network=* values without namespacing, with the exception of the Central American Highway Network (which overlaps with the Pan-American Highway).