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is an alternative to the Michigan left
A Michigan left is an at-grade intersection design which replaces each left turn with a permutation of a U-turn and a right turn. The design was given the name due to its frequent use along Michigan roads and highways since the late 1960s. In other contexts, the intersection is called a median...
format that uses roundabouts on the cross street. Left turns are prohibited at
the main intersection, which therefore requires only a two-phase signal. Vehicles yield upon entry to the roundabout, but if the roundabout has only two entrances, the entry from the main intersection does not have to yield. The roundabout diameter, including the center island and circulating roadway, varies from 90 feet to 300 feet depending on the speed of traffic on the approaches, the volume of traffic served, the number of approaches, and the design vehicle.
This configuration would reduce delay for the arterial street, increase capacity, and reduce the number of stops required. The primary problem with such a configuration is driver disregard for the left turn prohibition at the main intersection.
As of yet no agency has designed a complete bowtie road junction.
A grade-separated version of this junction results in a hybrid form with a diamond interchange
A diamond interchange is a common type of road junction, used where a freeway crosses a minor road. The freeway itself is grade-separated from the minor road, one crossing the other over a bridge...
called a dumbbell interchange
, where 2 raindrop roundabout
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...
s are fused together. This is basically a squashed version of a roundabout with a by-pass (usually overpass) for the main road. The advantage is that the narrow center of the two roundabouts need only a small footprint under the overpass. A disadvantage is that traffic needing to go left (in countries where is driven on the right) must make a series of curves that can be uncomfortable.