According to NC DOT they use a bunch of different varieties. It's under the plant list for "shrubs" for whatever reason.
http://www.ncdot.org/doh/operations/...st/Shrubs.html Hemerocallis-Daylily (thousands of varieties available)- D to E, G, FL
According to the NC DOT web site, the landscaping supervisor is Bob Kopetsky, (919)733-2920 ex 53.
The lillies were grown by prisoners at the Caledonia Prison Work Farm.