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"Geometry tells us that the traditional four-way intersection is inherently dangerous," writes Emily Badger. "When you plot all of the potential points of conflict on a diagram – and transportation engineers actually do this – it turns out that vehicles have 32 distinct opportunities to collide into one another at the nexus of two two-lane roadways."
"With that geometry in mind, it becomes clear what we need in the holy grail of intersection design: a scheme that would eliminate left-hand turns while still enabling drivers to move in all four directions."
"John Sangster, a doctoral candidate at Virginia Tech and an alternative intersection enthusiast, introduced us to several and pointed us to some spellbinding animations from the Applied Technology and Traffic Analysis Program at the University of Maryland (many thanks to researchers there for sharing these clips)."
With such exotic names as the Jughandle, the Superstreet, and the Diverging Diamond, and even wilder traffic patterns, "these designs are not an easy sell."
"In theory – i.e., in conflict-point diagrams – these intersections should be safer than more traditional ones," says Badger. "But there are two caveats to that promise: Sangster is really talking about safer intersections for cars. Pedestrians and bikers aren’t figured into any of these models, and Sangster has yet to encounter designs that do a good job of incorporating them (or transit). There also isn’t much hard data on the safety of these designs because so few of them have been built (and even accurately modeling them on a computer can be tricky and expensive)."