At Mesita, the highway originally followed what is now NM 6 to east of I-25 at Los Lunas. It passed through Albuquerque from south to north along Fourth Street, part of the historic El Camino Real de Tierra Adentro (El Camino Real). The highway is now replaced with I-25 through Santa Fe to, almost, Las Vegas (Historic 66 turns south before reaching Las Vegas), though several old sections exist which are barely (if at all) driveable. From south of Las Vegas back to I-40, the road has been replaced with US 84. After I-40 was established, travelers were no longer able to pass through the main towns.