A new paper by David Eichler, Hillel Bar-Gera and Meir Blachman in Networks and Spatial Economics describing perhaps the strangest street network you will see (sadly behind a paywall):
Vortex-Based Zero-Conflict Design of Urban Road Networks : "A novel approach is suggested for reducing traffic conflicts in at-grade (2D) urban networks. Intersections without primary vehicular conflicts are defined as zero traffic conflict (ZTC) designs. A complete classification of maximal ZTC designs is presented, including designs that combine driving on the right side in some streets and driving on the left side in other streets. It is shown that there are 9 four-way and 3 three-way maximal ZTC intersection designs, to within mirror, rotation, and arrow reversal symmetry. Vortices are used to design networks where all or most intersections are ZTC. Increases in average travel distance, relative to unrestricted intersecting flow, are explicitly calculated for grid-networks of sizes 10 by 10, 10 by 20 and 20 by 20 nodes with evenly distributed origins and destinations. The exact increases depend primarily on various short-range conditions, such as the access to the network. The average distance increase in most cases examined is up to four blocks. These results suggest that there is a potential for the new designs to be relevant candidates in certain circumstances, and that further study of them is worthwhile."
Vortices are of course in a sense just giant roundabouts. The Magic Roundabout of Swindon is the most complex I know of. This can also be seen in parts in neighborhood traffic calming districts. The unrestricted intersections could become roundabouts to avoid conflicts.
Note: Route factor = what we call Circuity, I think the authors overestimate the additional distance traveled, since people will orient their trips to the network.