For the next eight minutes, we're going to talk about traffic. Why? Because it's fun to know things! For example, did you know the study of traffic flow is an insanely complex field of mathematics and civil engineering? I know nothing about either of those things, but since we're on the internet there's nothing stopping me from pretending like I do! Traffic is frustrating for everyone, but especially for those who are working to improve it. If you're an engineer and you're trying to figure out the best design for a building, you could eventually find your way to a solution. But, if you're an engineer trying to figure out how to design roads for mass transportation... Good luck! The amount of factors involved in the flow of traffic are practically endless! The reactions of individual drivers, the fluctuating population of communities... the activity level of various locations during any given time of day, motor vehicle accidents... road construction... road conditions... the city's budget... the weather... The list is long and our runtime is short, you get the idea. Perhaps the biggest headache for the folks in charge of road construction is the dreaded interchange. A road junction where you can access major highways through entrance and exit ramps. Highways are high speed, but eventually, you need to get off of them, so that means slowing down. Interchanges are utilized to provide a safe method for cars to either get on the road or get off the road while avoiding the rest of the cars that need to keep going. Here's the problem though, intersections are TERRIFYING. Where two two-lane roadways intersect, there are thirty-two opportunities for drivers to collide into each other. Have fun sleeping tonight knowing that, but there's good news to be had. Engineers are finding ways to fix this.
Enter the Diverging Diamond Interchange. First employed in 1970's France, the design has been retooled and is now slowly, yet surely, making its way to the United States. I know this because I live in Springfield, Missouri, the first city in the US to use them. Springfield is the perfect mass transit guinea pig.
It's a former small town with a growing population that has the perfect mix of back roads and multi-lane monstrosities. Traffic fluctuates depending whether college is in session or not, and on top of that, being smack dab in the middle of Tornado Alley means our fair city can be used to test the latest and greatest traffic innovations against a variety of elements. The first Diverging Diamond Interchange in America was opened here on June 21, 2009, at Kansas Expressway and Interstate 44. If you're from around my neck of the woods, you know this area was notorious for backups during peek hours of the day. Like, one to two-mile backups.
Waiting twenty-five minutes or more was not uncommon, especially in the event of an accident. Today, thanks to the Diverging Diamond Interchange, traffic moves through this area in a matter of minutes. In fact, the Interchange was such a success story, Popular Science magazine featured it as one of the best new engineering innovations of 2009. Today this Interchange design has expanded to other trouble spots in the city, including National Avenue and James River Freeway... Kansas Expressway and James River Freeway... Chestnut Expressway and Highway 65... and Battlefield Road and Highway 65. Let's head out to this one and see how it all works. This is the intersection of National Avenue and James River Freeway. Two high traffic roads that have tons of congestion during peek hours thanks in part to the nearby hospitals, which account for a large portion of Springfield's employees. This is what it looks like when you are driving down National, and you cross over James River. Taking a right onto the freeway seems pretty straightforward. But driving straight through involves crossing over to a completely different side of the road and heading down a windy path of windy-ness. All of this looks and feels terribly confusing the first time you do it. The tilted traffic lights in the middle here made me freak out the first time I drove past them, yet for whatever reason, when you follow the dotted line... you're not sure why it works, but it just does. Things look like a convoluted mess of lines, lights, and barriers from the ground... but when you take to the skies, things become a bit clearer. Here's a quick mock-up of how things worked before the new system: Intersections were placed on either end of the entrance and exit ramps, which resulted in constant stops and traffic backups here, here, here, here, here and here. The new system temporarily shifts the traffic into the opposite lane, and allows vehicles leaving an easier way to exit, while the vehicles continuing down the road can move along at a steady clip controlled by traffic lights. This allows for two-phase operation at all signalized intersections, cars no longer have to clear opposing traffic when making long turns, making things much safer. Long story short: The new system is designed to shorten the time you're stopped, and these barriers coupled with this lane design eliminate opportunities for car accidents. Check this out, huge semi-truck takes the exit ramp onto National Avenue. Under the old system, this semi would either have had to stop at the intersection and wait for a green light, or if there was a designated turning lane, he or she had to stop and wait for room to make his or her turn while having an obstructed view if other cars happen to pull up too far. This means the truck could be stopped for around sixty seconds or more, which would cause a traffic backup on the ramp, which would stretch out onto the freeway itself. Very dangerous.
A lot of accidents happen this way, believe me. The new system?
He yields for a few seconds... and he's on his way! Or she... you get what I mean. The truck's stop time is shortened, there's plenty of space for other vehicles to cohabitate, the driver's field of view is no longer obstructed, and because the same system is being employed on the other end of the interchange, the traffic that stopped the truck before is moving. So...yeah, no backup. By the way, I love this. Check out how easy it is for big rigs to make a left onto the highway now. No stop. Easy visibility and they've eliminated the possibility of accidents from oncoming traffic because there IS no oncoming traffic.
That's been shifted to the other side of the road. Flip the pic around, and you'll see the benefits go both ways. Now maybe this makes sense to you, maybe it doesn't. But let's address the biggest complaint naysayers seem to have about this design. Mainly: "It's too confusing to know what to do!" It really isn't. The cool thing about this design is that... well, you don't really have an opportunity to mess up. If you had never seen this intersection before and you suddenly came upon it, you'd come to a stop at the red light, and once it turned green, you'd follow the lane... and you'd get through it! These barriers prevent you from driving anywhere other than where you are supposed to go. The road itself is designed to eliminate the chances of collisions. There are thirty-two potential accident spots at a regular interchange, this design lowers that to fourteen. Now, when the Diverging Diamond Interchange was first proposed in America, it got a lot of flak from this guy, Charles Morone. A "recovering" engineer whose major complaint was that the design was ugly, unfriendly to pedestrians and likely that it looked so wonky, that more accidents would be caused by people who didn't understand how it worked than anything. In fact, he made this- like- cutthroat video lambasting the design in 2011 practically forecasting its utter failure. Well, it's been seven years and rather than spawning the Interchange Apocalypse it turns out injury accidents at these locations have seen a sixty percent drop. The study of traffic and mass transportation systems is incredibly complicated. I just can't explain it all in a YouTube video. The point is that there's no magic bullet to stopping traffic jams and cities have to do the best with the money they have. So, the next time you see annoying road construction, just remember that although road improvements sometimes seem to move at a snail's pace, things are improving. And a lot of people are working really hard to make sure you arrive at your destination safely. Also, while I have you here... these are turn signals, they let other drivers know what you are doing, and you should use them! ... See ya! Thanks to my patrons. I get contacted a lot by teachers who show my videos in their classrooms... if there's a topic you would like me to cover, then let me know in the comments below and I'll pretend to consider it. Also, if you're really bored, I have linked to a thirty-three-page document about the Diverging Diamond Interchange by the Missouri Department of Transportation. But before you do that, share this video with everyone on earth. And subscribe to my channel... or don't, I don't really care.
These videos just make me want to play Cities: Skylines.
I wish California would adopt this.but we all know it would take 25 years to build one intersection, let alone the whole state
I still feel that this type of intersection could be absolutely perfected if you raised one of the thru-lanes above the other so you could avoid intersections completely and just have merges and splits. You would never have to stop if that was the case and it would be impossible to fuck up.
It would probably cost quite a bit more though.
EDIT: Okay it is called a DCMI, I get it. Please read the other comment replies before you all post the same thing!
Thanks for sharing. It’s coming to my town. Can’t be worse than the current situation is.
I encountered this interchange a few years back knowing nothing about it and it was very intuitive and I had no issue.
After I went through it I was extremely impressed! It just makes sense.
but why does the lane have to cross over for that to work?
I see now , it offers relief for the other onramp , wowI see now, it's so they can make a left onto the highway, wow
So each side, has an opportunity to:
Take a right, before they cross the highway on the bridge
OR
Take a left, after the bridge
Because the road put them in the left lane already
Really elegant, beautiful - /r/oddlysatisfying
City Skylines in a nutshell
One just completed near where i live. So far so good. So many other overpasses here have four stop lights just to get on free way.
I've been playing a lot of Cities Skylines and I have dreams about traffic engineering now.