As others have said, wide two lane so plenty of room for others to pass. If you've got the time, stay overnight in Arco at either Mountain View RV Park or the KOA, we've stayed at both and are both nice. Then take the tour at EBR-1, first nuclear power plant. Visit Craters of the Moon and drive up past Mackey and visit the earthquake site. All interesting. At the intersection of Hwy 75, there is a nice rest area with plenty of room for you to pull in, but there are other wide shoulders for you to pull over too along the way.
2011 Bighorn 3055RL, 2011 F350 DRW 6.7L 4x4 Diesel Lariat and Hensley TrailerSaver BD3, 1992 Jeep ZJ and 1978 Coleman Concord Pop-Up for remote camping
Dave & Renee plus (Champ, Molly, Paris, Missy, and Maggie in spirit), Mica, Mabel, and Melton