Saturday, January 28, 2023


Navigating diverging diamond interchanges in your RV

Driving your RV down the road demands your full attention. This is especially true when you come upon an unfamiliar road configuration like a roundabout or a Diverging Diamond Interchange (DDI). Like most everything else with RVing, it’s a good idea to learn as much as you can ahead of time. So here are some tips for navigating diverging diamond interchanges in your RV.

Background on DDIs

It all began with a term paper. Graduate student Gilbert Chlewicki began to pursue his master’s degree in traffic engineering in the fall of 2000. Gilbert had been interested in roadways since elementary school, often drawing different configurations and sketching unique highway designs. Chlewicki’s term paper was a success, and he continued to perfect his design.

On a trip to Versailles, France, Chlewicki saw a DDI in actual use. He was disappointed to learn that he was not the first to design the unique interchange, but at the same time very excited to see that the idea actually worked! (DDIs have been in use in France since the 1970s.)

Benefits of a DDI

The diverging diamond interchange has several benefits. Here are just a few:

  • Better sight distance at turns
  • Fewer conflict points
  • Potential points of conflict spread out throughout the interchange
  • Pedestrian crossings are shorter
  • Simple left or right turns from every direction
  • Increases left turn capacity with fewer traffic lanes
  • Greater functionality during power outages
  • Cost savings maximized

How to drive on a diverging diamond interchange

First, watch for signage—on overhead and street signs and on the roadway itself. Set your navigating device to your eventual destination and follow the directions it verbally gives you. Watch for barriers that may also be in place, helping to guide the traffic. Take your time. If you must change lanes, signal your intentions.

Here’s a video that will help you visualize the DDI ahead of time, so you’ll be better prepared to drive your RV safely through one.

Have you driven your RV through a diverging diamond interchange? Where was the DDI located? Do you have additional tips to share? Please do so in the comments below.



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10 hours ago

There is DDI on I-10 at the Houghton Rd. exit in Tucson, AZ

John Boy
1 day ago

My first and only encounter is in Branson, MO. When my wife and I came upon it we said what the ????. We were in our car at the time. We don’t have a need to drive our Motorhome through this part of Branson.
Great article and EXCELLENT explanation how to drive through a DDI.

2 days ago

DDI, What a stupid idea.

Last edited 2 days ago by JAMES
Daniel Merkovsky
2 days ago

I strongly dislike the DDI interchange. There is one in Washington, PA on I-70. The concept is very confusing when you first come upon the DDI. It is completely disorienting the suddenly have to drive on the “wrong “ side of the road. This is really an issue at night or in low visibility conditions when you suddenly see headlights coming at you in what was your lane. I consider the DDI to be quite dangerous.

Neal Davis
3 days ago

There is one off I-40 outside (eastward from) Knoxville, Tennessee, possibly the Pigeon Forge exit but in the opposite direction from Pigeon Forge. We drove another one, but we cannot remember where it was. We drove it last summer. Guess I need to annotate our travels better, huh? 😉

Donald N Wright
3 days ago

This is so cool. Thank you for explaining it.

3 days ago

Yes, thanks for the explanation!

Douglas L Roberts
3 days ago

The I-95 junction with I-595 just south of Fort Lauderdale, Fla., is now a diverging diamond (at least when traveling south). The diamond causes westbound traffic to travel counterintuitively to the east for a short distance before it swings around to the west. A similar diamond is about to open at Glades Road and I-95 in Boca Raton.

3 days ago

Good gravy, have never heard of such a thing. I’m still trying to figure out clover leafs. Even if I figured it out, my wife would be screaming at me for being on the wrong side of the road. And after I have figured out downtown Atlanta during rush hour, a new learning curve for me. “Country roads take me home to where I belong.”

Diane McGovern
3 days ago
Reply to  KellyR

Thanks, Kelly. Now I’ll have that song running through my head all day. 😆 And I’ll be thinking of my 18 acres of gorgeous mountain property (“where I belong”) waiting for me. BTW, thanks to John Denver, my two license plates are MTNMAMA and MTNMOMA. Have a great day! 😀 –Mountain Mama at

3 days ago
Reply to  Diane McGovern

No matter where I roam or end up, I’m still a country boy. You just can’t take that out of me.

Diane McGovern
3 days ago
Reply to  KellyR

Good for you, Kelly. I’ve always been a “mountain mama” (although I grew up just on the north edge of Seattle). When in school, everyone I knew wanted to go to Hawaii. They all thought I was nuts because I wanted to go to Alaska. (Too much Jack London, I guess.) Now I know my dream property is up there waiting for me, if/when I have time to go up there. Luckily it’s only about an hour drive from my home. But when I’m working 28/7/365 😆 it’s hard to fit it in. This year, however, I’m going to figure out how to do my work from up there for a few hours at a time, just to get my fix of the mountain property. No cabin or anyplace to sleep, so I’d commute just for part of a day. But still…that sounds sooo good. Just gotta watch over my shoulder for black bears, mountain lions, etc. Minor distractions like that. 😆 Later, Kelly. 😀 –Mountain Mama at

3 days ago
Reply to  Diane McGovern

No cabin, no place to sleep. Hmmm – Have you ever thot of an RV? Maybe a nice B? Commute and sleep in the same place. There is a website I like that tells you all about RVs. They have beds, bathrooms and all you need. is a good place to start.

Diane McGovern
3 days ago
Reply to  KellyR

An RV? Now, why didn’t I think of that?! 😆 Yep. It’s a possibility. There is sometimes some vandalism up there, since it’s kinda remote but accessible. So, I’m considering getting a “portable cabin,” if you will, and then I won’t worry about my cabin getting broken into when I’m not there. And I’ll check out that Thanks for the great suggestion, Kelly! 😆 Take care. 😀 –Mountain Mama

Diane McGovern
3 days ago
Reply to  KellyR

Ha! I just combined two of our articles together in my (sometimes strange) brain and decided people can use a compass to navigate diverging diamond interchanges. 😆 Take care, Kelly. 😀 –Diane at

3 days ago

I just have to wonder how they work if the power is out in the region and the lights don’t work! I would hope they have some sort of RELIABLE long term backup power for the lights and hopefully if needed it will be available to avoid a total disaster.

3 days ago

We have several DDI’s in the Reno/Sparks area. Best idea for interchanges. Numerous roundabouts also. Each has its best locations. You just have to pay attention and know where you want to go before you enter each one.

3 days ago

Crossing I-5 @Lacey, Washington. GPS: 47.063555, -122.76539.

Marvin exit (ie the one to Cabela’s and Shipwreck Beads)There is a fairly complete list of all of them here

Martyn Price
3 days ago

Great article. I think that I have driven a couple of divergent diamonds without knowing what they were. The video demonstrates how they are laid out thoughtfully and make for improved traffic flow. Would be nice to see more driver education.

Roundabouts by contrast, seem to elicit near universal disapproval. Having grown up in Europe I think of them as second nature and a great excuse to drop down a couple of cogs, apply the power and practice my opposite lock techniques (when not towing that is). Just kidding- a little.

Seriously, I think roundabouts are either misunderstood in the US, or perhaps just over shadowed by a mindset of four-way-stop-ism. To me, the central purpose of a roundabout is to not have to stop before entering but to blend into the existing flow of traffic, choose the correct lane based on which exit is being taken, and to use turn signals to indicate those intentions. Roundabouts are not for the timid or mindless.

Last edited 3 days ago by Martyn Price
3 days ago

It’s a big bonus for the signal-light / overhead-arm manfacturer–at least 8 in less than 300 feet

3 days ago

There are quite a few of these in the St. Louis, MO area. One of the first was at I-270 & Dorsett, now at I-70 interchanges at both the Fifth Street exit in St. Charles and the Mid-Rivers exit in St. Peters, and apparently under construction at all of the I-70 exits in between.

Steven N
3 days ago

The first time I saw a DDI intersection was east of KC, Oak Gove Missouri, exit 28 on I70. The first time it was dark and a bit confusing but since then we have transited it in the daylight several times and it isn’t that bad. If you pay even the least bit of attention and follow the signs it isn’t a big deal. A lot of people in the comments are complaining about things that have nothing to do with the design of roundabouts and DDI intersections and more to do with a) a general problem with change and b) how so many drivers are mindless self centered a-holes who don’t care about anything but their cell phones (social media), chai lattes, blaring music, etc. You will never be able to do anything about the self centered a-holes but you can learn to come to terms with change because the only constant is change!

Jesse Crouse
3 days ago
Reply to  Steven N

Could not have said it better.

3 days ago

We have been through one down by Springfield, Missouri. It was a little confusing the first time we went through it, but got a little better each time we did. Just followed the arrows and signs. First few times we were just driving our car, but the last time we were driving our truck and pulling our 5th wheel. I think they’re better than roundabouts.

Andrew R.
3 days ago

There is a DDI at the I-95 Yulee FL interchange, seems to work well IMO. I like that turning left or right to access interstate is very easy.

3 days ago

We have one of these on our Main St. that goes under the freeway overpass. Supposedly it helps with the traffic getting on the freeway. Until you get used to it, it’s very difficult to see where the traffic is coming from because it is coming from the other side of the road. Lots and lots of accidents happen here. I try to avoid it.

3 days ago

Have not driven thru one of these. New England DOT’s have fallen in love with round abouts.
3 days ago

I’ve taken the MH through the DDI on the west side of Madison, WI numerous times and through one on the East side of Appleton in my car probably 50 times. Don’t see why anyone would have trouble if you watch the signs and obey the lights. the curves are more gentle than cloverleafs and roundabouts.

3 days ago

Wow – I’ve been through both Madison & Appleton plenty of times but haven’t encountered a DDI…in fact I’d never heard of them. I really appreciate this heads-up

3 days ago
Reply to  Rebecca

From the WI DOT website

I-39/90 and WIS 11/Avalon Road interchange, south of Janesville WIS 441 and Oneida Street interchange, AppletonI-39/90 and WIS 26/Milton Avenue interchange, JanesvilleI-39/90 and WIS 81 interchange, Beloit Not one listed near Madison but this might be out of date.

Last edited 3 days ago by Snayte

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