J- turns are located on 4-lane divided highways and prevent direct crossing and left-turn movements. These side road movements are made indirectly by making a right turn, traveling about a quarter-mile on the divided main road, and then making a U-turn to proceed in the opposite direction on the main road toward the intended destination. A J-turn reduces a significant number of the severe, right-angle, “far” side crashes. Relative to other improvement concepts, it is a low-cost treatment that can be quickly implemented, does not require property acquisition or relocation of homes and businesses, and minimizes environmental impact.
–Wis DOT on YouTube