By Gail Marsh
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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RVT1260
Since roundabouts weren’t discussed, they are designed to accommodate large trucks and busses. There is skirting on the left side to allow larger vehicles to run off the lane edge without damage.
Roundabouts are traffic calming and reduce the frequency and severity of accidents. The signage, as required by the MUTCD, will inform you which lane (if there’s more than one lane) to safely continue on your preferred route.
“”There is skirting on the left side to allow larger vehicles to run off the lane edge without damage.””
Called ”Mountable curbs”. Reduces the outer diameter of the roundabout, reducing the land necessary for construction.
DDI’s are an ‘optical illusion’ looking for a place to happen.
Like ’roundabouts’ aka ‘traffic circles’, both work well when one understands their operation.
I can’t stand all the roundabouts they have in Colorado. Most of the people driving cars or normal vehicles are ruthless and always in a hurry, so they are very disrespectful of us in our rigs. I prefer a good old traditional exit.
I hate roundabouts and know I’d hate DDI’s. We have a roundabout in Avoca, Pa they had to paint airplanes on the road so people could find the Airport.
Thanks Gail. I’ve driven through several DDIs – I can’t recall where anymore. There’s one in Pine Island, MN over Hwy 52. It’s not a high usage one. I’ve had no troubles, just read the signs and pay attention.
We have both ddi’s and roundabouts in Reno NV. Roundabouts are used at intersections and work well when new traffic yields to the traffic already in the roundabout. Ddi are used under freeway overpasses and seem to allow for a smooth flow of traffic on and off the freeway ramps. Most people are aware of how they work and there are few problems.
Have been on two DDIs. Both times pulling a 33-foot 5er. One at the St George Blvd and I-15 interchange in St George Ut. A very busy interchange. Two College Drive and I-25 interchange in Cheyenne Wy. A very busy interchange with two truck stops one each side of the interstate. I like this set up because it makes a left turn to enter the on ramp very easy and a left turn on the off ramp very easy. The only problem I have had is knowing which lane to be on the off ramp left turn, especially if I want to make a righthand turn once off the end of the interchange. Once I figured out what lane to be in it was super easy to use this type of intersection.
Yep, I admit DDI’s are radically different. But driving thru one, following the signage, is as easy as a regular interchange. Where on I-40 is the DDI in the video shown?