It’s a rural, undivided, four-lane road, with an unreasonably low speed limit of 40 mph. There is usually at least one sheriff sitting in one of the few parking lots along the road, hidden behind a tree or a sign, clocking people. If you can, use Shaffer instead, at least 40 mph on that road is reasonable (and it was set by the City of Atwater, not Merced County, so this is no surprise).