Could These Crazy Intersections Make Us Safer?

Geometry tells us that the traditional four-way intersection is inherently dangerous. 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. Cars can crash into each other while merging or diverging from a given lane. Then the worst action happens right in the middle of the interchange, at that perilous point where vehicles turn left across oncoming traffic.

There, the geometry gets even more gruesome. Cars colliding head-on, or at a right angle to each other, are much more likely to cause serious carnage than two vehicles merging at a shallower angle (as happens on a right-hand turn). This is what a traditional intersection looks like when you analyze it as a potential death trap: