It's going to be really interesting to see what intersections look like once we no longer allow human drivers behind the wheel. We can only hope this will happen during our lifetime.
"And we all know how that's gone in America with the simple roundabout."<p>Roundabouts are not unpopular, and exist in cities like DC with no one complaining. The reason why roundabouts are unpopular is because city meddlers often put them in places where their purpose is not to mitigate accidents but to attempt to limit speeding through side streets, with negligible (if not negative) effect on traffic safety.
This reminds me of the great transformation of Drum Hill Rotary into Drum Hill Square:
<a href="https://www.google.com/maps/place/Drum+Hill+Rd/@42.6225607,-71.3666283,17z/data=!4m2!3m1!1s0x89e3a35cf6c32ab7:0xfc19e146f5ee894e" rel="nofollow">https://www.google.com/maps/place/Drum+Hill+Rd/@42.6225607,-...</a>
The resulting design is ridiculously confusing and unintuitive. The first time I was driving to it I thought:
"WTF were they thinking? How do I get into the right lane?"
Then it changed to
"Woah, I got lucky, I'm sure I will get confused the next time"
and then
"OK, somehow I keep getting it right"
and
"Wait, I am no longer stuck in traffic here?"
"Not even at 5pm?"
"...woah?"<p>Yes, designing the traffic lanes works.
It's interesting to note that much of the gain in automobile safety over the past 50 years has been offset by an increase in miles driven due to increased sprawl [1].<p>It seems like this sort of intersection, while possibly being safer, would encourage even more sprawl due to its scale, and pedestrian-unfriendliness.<p>[1] <a href="http://www.planetizen.com/node/68200" rel="nofollow">http://www.planetizen.com/node/68200</a>
I also note the the "lights" in the simulation are cycling <i>WAY</i> faster than I have ever seen a traffic light cycle in the US.<p>A whole lot of intersections in the US would likely improve with that simple "innovation".<p>People are less likely to crash a yellow-to-red light when they know that their turn is coming again in 30 seconds. Make that 5 minutes and streams of people are going to crash that light.
I used to live near the Mixing Bowl [1] (not exactly an inspiration in city planning), so I just wonder how these would hold up under congestion. The mixing bowl proves you can do anything with ramps (& no lights!), but building flat intersections seems much harder.<p>Building freeway ramps isn't really that hard, though, so I don't see the point in restricting dimensions. It's good not to let it get out of hand like VDOT, but concrete is pretty cheap. Maybe if you've got a lot of 45mph roads connecting you'd want good lighted designs. Where I live now it's all 40s connecting to 55s connecting to the interstate, so it'd be pretty moot.<p>Planning for road speeds & traffic rates seem far more important than keeping things flat.<p>[1] <a href="http://en.wikipedia.org/wiki/Mixing_Bowl_(Springfield)" rel="nofollow">http://en.wikipedia.org/wiki/Mixing_Bowl_(Springfield)</a>
I used to live near a road that was designed similar to the "Continuous flow" model. It wasn't quite that elaborate, but Palatine Rd. just north of Chicago has "local" and "express" lanes. (Or was it Dundee Rd.? I forget.) I have no doubt it flows more efficiently than other roads, but I consistently had people drive into the wrong lane directly at me. I've never had that on other streets. So the question is - do these trade efficiency for basic safety?
That "diverging diamond" would terrify me.<p>Seeing a car moving at high speed on the right in a parallel trajectory is a deeply ingrained alarm bell that I'm in the wrong lane.<p>US Interstate 35 in Austin at 51st Street used to (may still have) have an overpass lane like this and it took a <i>LONG</i> time to get used to without it causing "Danger Will Robinson" reactions.
<i>Continuous Flow</i> model reminds me of divide and conquer sorting algorithms.<p>Most elaborate roundabout( with traffic lights ):<p><a href="http://i193.photobucket.com/albums/z202/keber1/razno/tomaevo3-pzr.jpg" rel="nofollow">http://i193.photobucket.com/albums/z202/keber1/razno/tomaevo...</a>
amazing. I've always fantasized a "diverging diamond" for the I-5/Genessee exit in San Diego. There are space constraints (the freeway is in a canyon) that prevent more traditional designs, and the exit is a nightmare, causes atrocious traffic snarls.<p>I had no idea that someone had actually made one.