Archive for Wednesday, December 1, 2010

KDOT eyes diverging diamond to help traffic flow

Project on I-35 scheduled to be completed by 2014

December 1, 2010


Diverging diamond diagram.

Diverging diamond diagram.

Move over roundabout, there’s a new trend for how traffic should flow through busy interchanges.

It’s called the diverging diamond, which involves motorists briefly driving on the opposite side of the road. Kansas will see its first by 2014.

The Kansas Department Transportation this week announced that a diverging diamond will be used at the intersection of Interstate 35 and Homestead Lane in southwest Johnson County. The interchange project, which is set to begin in 2012 and be completed by 2014, will provide access to Burlington Northern Santa Fe Railway’s proposed 443-acre rail-truck shipping center near Edgerton.

KDOT decided to build a diverging diamond because of a high volume of traffic through the intersection and the large number of left-hand turns expected to be made once traffic leaves the interstate, KDOT spokeswoman Kim Qualls said.

To best understand how the diverging diamond works, check out the diagram with this story.

Basically, traffic will enter and exit the interstate in the traditional diamond pattern; however, once motorists arrive at the overpass over I-35, traffic switches to the opposite side of the road.

This allows for traffic getting off both the south- and northbound lanes of I-35 to make an automatic left turn without cutting in front of oncoming traffic. This is the key safety feature of the design.

On either end of the overpass, traffic crosses back over to continue on the correct side of the road. Traffic movement is controlled by a traffic light on both ends.

“It allows more free-flow type movements with less delays,” Qualls said.

While a common feature on European highways, the first diverging diamond in the United States opened in 2009 in Springfield, Mo.

So far it’s been deemed a success, said Jorma Duran, community relations coordinator for the Missouri Department of Transportation.

Traffic accidents at the intersection have dropped and a once bothersome bottleneck has disappeared.

“You eliminate the risk of having to dodge in front of oncoming cars,” Duran said.

MoDOT built and opened another diverging diamond in St. Louis this year and is working on a few others. Other states, such as Utah and Georgia, also have embraced the traffic design.

Along with being safer and moving traffic more efficiently, diverging diamonds are less expensive to build, said Jim Hanni, Kansas AAA executive vice president of public affairs.

“It might take a little bit of getting used to. I’m certainly sensitive to that,” Hanni said. “But if you look at all the engineering data, it’s safer. There are just fewer conflict points for crashes, not to say anything about the cost savings.”

For it to work, Hanni thinks there needs to be plenty of signs and road markings alerting drivers of the changes.

In the case of the diverging diamonds in Missouri, Duran said it’s clear where drivers need to go.

“Even if a driver never heard of a diverging diamond, they would have to be utterly confused to get on the wrong side of the road and not follow the signs,” Duran said.


Driving A Diverging Diamond Interchange


Aerial view of a diverging diamond interchange


John Hamm 7 years, 3 months ago

“Even if a driver never heard of a diverging diamond, they would have to be utterly confused to get on the wrong side of the road and not follow the signs,” Duran said. Oh boy I can't pass this bit of idiocy up! And to this comment I reply, "And how many times a day in these United States do "confused" drivers drive on the wrong side of the road?" Heck it takes months for Kentucky and Tennessee Streets to become "safe" again after a new batch of students move in every fall! And there's absolutely nothing confusing about two one-way well marked streets.

Ron Holzwarth 7 years, 3 months ago

"absolutely nothing confusing about two one-way well marked streets."

I had to snicker a bit at that - I used to work with a woman who had an accident on TN or KY street, forget which one, with a woman who was from out of town.

The woman she collided with was from a small town, she was going the wrong way, and she had never even heard of a one way street!

blindrabbit 7 years, 3 months ago

I'll bet the insurance and liability lawyers are buying-up the surrounding property for their advertising signage anticipating crash business from the confused drivers. Need to get a tow truck business signed-up as well

Ron Holzwarth 7 years, 3 months ago

If you're a confused driver, your insurance company is going to need a defense lawyer, I'll grant you that much. But, judging from my experience in helping as an interpreter, the confused driver's insurance company just settles out of court.

Blessed4x 7 years, 3 months ago

Actually the diverging diamond is quite safe. It eliminates turning movements at a signal which speeds up flow through the interchange (the signal only has two thru movements and no turning movements). The raised medians and markings funnel you through the interchange with little thought or confusion. It looks like a confusing mess, but until you've driven one, you really do not have all the facts and are jumping to conclusions. They are quite efficient and safe. Really the only potential impact areas are in the merging/weaving sections as those getting off the mainline are entering the cross street traffic while those that are on the cross street are trying to merge over to enter mainline traffic. However, this is a pretty standard movement at a lot of interchanges and unavoidable as long as you wish to maintain full access at the interchange.

Kansas has been exploring this type of design as a possible solution to busy interchanges for some time. The article is somewhat in error by suggesting that the diverging diamond will replace roundabouts. They are two different animals and are used for two different purposes. There is a design commonly referred to as a "Dog Bone" that consists of two roundabouts, one on either side of the mainline, constituting the interchange, but they are very rarely used.

Please do not let phrases like "driving on the wrong side of the road" paint your view of this design solution. Those are merely catchy lines that the journalists use to shock readers.

WHY 7 years, 3 months ago

I went through one of these this weekend in Missouri. I just sat there for a minute trying to figure out what to do and then watched the other cars criss-cross. It will make a great DUI checkpoint because if I wasn't sober there is no way I would have gotten through.

just_another_bozo_on_this_bus 7 years, 3 months ago

From the diagram, it looks like the criss-cross is controlled by a traffic light, which should eliminate the confusion. Is that correct?

BrianR 7 years, 3 months ago

I think the light, coupled with a short prayer should do the trick.

Edwin Rothrock 7 years, 3 months ago

Reducing the number of conflict points at intersections greatly reduces not only the number of injury accidents, but also the total number of accidents. Innovative engineering like divergent diamond interchanges is proven to make driving safer - even for easily confused people.

Those darn facts.

gphawk89 7 years, 3 months ago

This interchange design increases the number of conflict points for folks driving on the "non-limited-access" street. From zero conflicts to two. The directions cross twice, not quite head on but it seems like it. I don't see how this can be safer and is definitely more confusing than just driving on the right.

Ron Holzwarth 7 years, 3 months ago

It might take a bit of getting used to, but if you read the article closely, you'll see that the problem with that particular intersection is the very large amount of traffic making a left turn. And, a lot of that traffic will be semi trucks.

Have you ever seen a car that has been run over by a semi truck? I have, one time it was only a minute or two after it happened, and it's not a pretty sight. Closed casket funeral, for sure.

If there is any way to eliminate those types of accidents from happening, it should be done.

somedude20 7 years, 3 months ago

Like they said in the Corps, diamonds are forever, now give me twenty. Those, fyi, are hard push-ups to do a bunch of)

gphawk89 7 years, 3 months ago

I drive through one of these every day. Mixed feelings.

It does help left-turning traffic. This could definitely help when exiting the highway because both a left and right turn on red (after stopping) would be legal - at least in most states.

On the other hand, it absolutely prevents simultaneous two-way traffic on the street that intersects the highway. They cross - twice - almost head-on - so one direction or the other always has to stop, sometimes twice.

The complex lane markings seem to work but I have a feeling it will become a nightmare when they're covered with snow at night.

For folks that have a hard time guiding a car under normal conditions (I don't want to pick on the inexperienced or elderly, but let's face it)... well... I'd rather not be in the intersection the same time they are.

I've not seen any actual wrecks - yet - but have witnessed a few near misses.

I think these interchanges could be a help in the appropriate places, but they're definitely not a fix-all. The one I drive has not seemed to help congestion at all. I guess the state had to spend it's stimulus money somewhere - they sure advertised it on the billboards during the construction.

staff04 7 years, 3 months ago

Been through the one in Springfield several times. Not confusing at all, just pay attention. It is almost impossible to go the wrong way due to the raised medians, and the only way I could imagine an accident happening there is if someone ran the red light.

It seems pretty idiot-proof to me, so I'll look forward to at least a few uber-idiots proving me wrong.

fanaddict 7 years, 3 months ago

Agree...went through the Springfield one twice last problems at all, and it was with quite a bit of traffic.

Alan Tabula 7 years, 3 months ago

Looks like smooth traffic flow for motor vehicles, but complexities abound for bicyclists and pedestrians (though this is true of many other interstate interchange designs as well) ...

SeaFox 7 years, 3 months ago

It's illegal to ride a bicycle on interstates to begin with last I heard.

Alan Tabula 7 years, 3 months ago

The interchange connects the interstate with a local road -- that's where the bikes & peds are...

riverdrifter 7 years, 3 months ago

I've done the one in Springfield many times. No trouble at all even in heavy traffic The only problem I've ever seen with it was a fender-bender that had happened. Just pay attention. No texting or talking on the cell phone.

gphawk89 7 years, 3 months ago

"Just pay attention. No texting or talking on the cell phone."

To quote Hamlet: "Aye, there's the rub!" Some percentage of drivers don't pay attention and do text and talk on the cell phone.

Ron Holzwarth 7 years, 3 months ago

Yes, you're right. After all, the locomotive and automobile were invented there.

There's quite some argument about who invented the airplane, but Leonardo da Vinci sketched the first one about the year 1500.

Kris_H 7 years, 3 months ago

Can't wait to try one in Kansas City MO at night in the rain...NOT.

Ron Holzwarth 7 years, 3 months ago

Some people are resistant to change. For example, the cloverleaf intersection that is now common on Interstates all over the country, and also roundabouts. When they were first introduced in the United States, a lot of people had a great deal of trouble understanding how they were supposed to work. They thought traffic signals and four way stop signs were better.

Perhaps the Amish are right, and we should all go back to horses and buggies.

Ron Holzwarth 7 years, 3 months ago

Gimme a break, we won't need that! You get plenty of fresh air, and a wonderful smell from the horse's behinds!

Ron Holzwarth 7 years, 3 months ago

I'm quite sure something like this will be built at very few locations. That is, only in places that have rather unusual traffic flow, and where it makes sense to direct traffic in that manner. It seems to me that the article makes that clear.

independant1 7 years, 3 months ago

I think it's a wonderful idea. I love it!

Jay_lo 7 years, 3 months ago

Seems like if the whole idea was to prevent traffic congestion then the crossovers should be on different levels, then nobody would have to stop. Right lane over, left lane under.

It would take more space, but the idea wasn't to save space, but to ease congestion.

Watch the videos. It's great if you know which lane you need to be in "before" you get to the turn arrows.

I think a lot of first timers are going to be exiting by mistake and trying to find their way back on. Should be pretty simple after you've been through it each way a time or two.

whatadrag 7 years, 3 months ago

Implementing your idea would be wastefully expensive

Jay_lo 7 years, 3 months ago

Tell that to the families of those killed at the crossovers. I'm sure they would be glad to know how little you feel their lives are worth.

Expensive, probably, Wasteful, debatable. Unless you are talking about your moving expenses since you claim to live under a bridge and might be interested in relocating.

It's two little overpasses. They build them every day.

whatadrag 7 years, 3 months ago

You drive a car, you must be a traffic engineer.

I'm amazed at how little you know, yet how willing you are to bash a new, yet clever idea.

You're obviously unaware of how much cheaper an at-grade intersection is. They don't build "little overpasses" everyday.

How does that saying go? It is better to appear a fool and keep silent than to open your mouth and remove all doubt.

Jay_lo 7 years, 3 months ago

Also notice in the second video all the vehicles at a dead stop waiting to merge onto the main trafficway because there are no "get up to speed lanes". They have to merge from the ramp directly into a driving lane, which they can sometimes only do when traffic is stopped by the light.

I would hate to be sitting at the top of the on ramp at a dead stop and hoping that the hopped up trucker with little sleep behind me was paying attention, and not thinking it was just another" keep it moving" cloverleaf.

average 7 years, 3 months ago

"While a common feature on European highways"

Um, no. Before the one opened in Springfield last year, there were exactly two of them in the world. Both in France. This does not make them "a common feature on European highways".

It is a beautiful and ingenious design, though, for certain traffic conditions (heavy left turn traffic) and with budget constraints (it needs some additional land, but it can generally re-use an existing bridge from an over-used conventional diamond interchange).

BearCat 7 years, 3 months ago

Talk about being confused, whoever made the first video is. When it displays "Traveling North to East" it is actually going south and then turning east, and when it displays "Traveling South to East" it is actually going north and turning east. Hopefully, this isn't a government-made video :)

TopJayhawk 7 years, 3 months ago

I think the picture above is of the one in Springfield Mo, where Hgwy 13 crosses I 44. Drove it a few weeks back. It was confusing until I understood what they were doing. Actually it worked quite well. Hard to get in a wreck the way the islands funnel traffic.

irvan moore 7 years, 3 months ago

it would be a lot cheaper to put up a no left turn sign.

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