The highway department planners and financiers made the deal to build a new bridge crossing the Colorado just below Hoover Dam. This has greatly improved traffic flow, since there are no longer switchbacks to negotiate.
The security-conscious ensured that the lane-edge barriers are strong—and high. Thus, pedestrians have a fine view upstream of the dam, while typical passenger vehicles have a fine view of the concrete safety wall.
Or is this design intended to encourage tourists to stop for the view, then decide to pay hefty entrance fees for the visitor center (yes!) and for dam tours?