Missouri's Diverging Diamond Interchange

[roadman65]

I was wondering about everyone's opinion of the Diverging Diamond at the MO 13 & I-44 interchange in Springfield, MO.  To me, although strange to have you drive on the left like in the UK, it does have a great merit because you only have two signal phases.  You eliminate the need for left turn signals on MO 13. However, on the minus side, I feel, that the SPUI is just as effective, so really not much better, though making things more interesting to have another type of interchange thrown into the mix.

From what I understand its the first of its kind in this nation, chosen at the particular location, so we can say its waters being tested by Missouri. 

[Scott5114]

I've been through it. It's not as confusing as you'd think it is–MoDOT did a good job designing the geometry and traffic control devices, so the chance of driver error is low.

DDIs have one big advantage over SPUIs–the bridge is much narrower than is required for a SPUI. In fact, the DDI in Springfield that you mention was retrofitted onto an existing diamond interchange without having to modify the bridge at all other than adding barriers. That means that DDIs are much cheaper and quicker to retrofit onto an existing interchange than constructing a SPUI is.

[Revive 755]

From what I understand its the first of its kind in this nation, chosen at the particular location, so we can say its waters being tested by Missouri. 

Given the fairly widespread deployment - at least seven in Missouri, two near/under construction in Illinois, and probably at least one in many other states - I'd say the DDI is being tested in many locations.

It will be interesting to see where and when the first DDI fails to work as expected and is converted to some other type of interchange.

[bugo]

The Death Diamond is an experiment, and I see it being a failed experiment and for all of them to be converted to something else in the next few decades.

[corco]

Why?

[m2tbone]

The drivers in Missouri seem to be smart enough to use them properly.  I only foresee a lot more being built, especially in MO.

[Indyroads]

The Death Diamond is an experiment, and I see it being a failed experiment and for all of them to be converted to something else in the next few decades.

I don't see it causing any more accidents than a regular intersection, the issue remains with efficiency. It could be more efficient for traffic coming to or from the freeway but for large volumes of through traffic it would restrict traffic with the through lanes crossing each other at each side of the intersection.

[Alps]

A DDI gives each through movement 50% of the cycle. (Each direction has its yellow and all-red times, but that's a constant in this analysis.) For a SPUI, you have three phases in the cycle. The side ramps will typically use about 25%-30% of the cycle, and the main street left turns will typically use about 20% of the cycle. Guess what's left for the through movement? 50%! So it's not actually more inefficient from that perspective.
* What a DDI does better: You're moving left turns for 50% of the cycle instead of 20%, and you're moving ramp traffic 50% of the cycle instead of 25%-30%. If you have high ramp volumes (a major entrance to a commercial/business area from the freeway), a DDI can increase capacity over a SPUI.
* What a DDI does worse: Where ramp volumes are relatively light, you may only need 30% of the cycle to handle ramps and left turns. (I'll assume that we're looking at the same SPUI, just on the weekend or at nighttime.) Now your through traffic suffers. This can be an issue in downtown/entertainment districts where weekend and event flows have different patterns than commercial flows.

If a DDI didn't provide improved flow over a SPUI in certain scenarios, it wouldn't have been implemented.

[apeman33]

Just based on reaction I've seen posted on a local TV stations' page, people in Joplin hate the I-44/Range Line DDI. The general view seems to be that they think it's more dangerous than the cloverleaf it replaced. Me, I've been though it and I don't have any problems with it except that maybe people were driving through it a little too slow because it was weird to have to switch sides of the road.

[Alps]

Just based on reaction I've seen posted on a local TV stations' page, people in Joplin hate the I-44/Range Line DDI. The general view seems to be that they think it's more dangerous than the cloverleaf it replaced. Me, I've been though it and I don't have any problems with it except that maybe people were driving through it a little too slow because it was weird to have to switch sides of the road.

a) People who don't have a problem with it won't post about it.
b) People always have problems with new, unfamiliar scenarios until they adjust.

[jeffandnicole]

Just based on reaction I've seen posted on a local TV stations' page, people in Joplin hate the I-44/Range Line DDI. The general view seems to be that they think it's more dangerous than the cloverleaf it replaced. Me, I've been though it and I don't have any problems with it except that maybe people were driving through it a little too slow because it was weird to have to switch sides of the road.

a) People who don't have a problem with it won't post about it.
b) People always have problems with new, unfamiliar scenarios until they adjust.

c) Anyone can vote & comment on those polls, regardless if they have ever used it. Hell, they don't even have to be in the same state or country.

My guess would be most of the negative people haven't used it. From the air, or standing off to the side, it'll look confusing. From the driver's perspective, he's just following the lane markings, which easily guide him along the travel lane to the other side.

[M86]

I've driven through the DDIs in Joplin and Springfield. 

The one in Joplin needs better signage.  And the cloverleaf that was there is not missed. 

[huskeroadgeek]

Having been through the MO 13/I-44 interchange from the north on MO 13 many times-always turning left to head east on I-44, I think the diverging diamond is a major improvement over having to sit and wait to turn left. Same with the one at I-435 and Front St., which I've been through several times since it opened too(again, usually turning left to get on I-435). The idea of driving on the left side doesn't seem strange once you get used to it-plus it isn't for very long either.

[RoadSigma]

There is also one at Woods Chapel Road and I-70 in Blue Springs and personally, I kind of like them. I have no issues with them at all.

[Tom958]

If a DDI didn't provide improved flow over a SPUI in certain scenarios, it wouldn't have been implemented.

Are you sure? A DDI is a lot cheaper, and all it has to do is to provide enough of an improvement over the existing condition to justify the (much lower) cost. Or would Missourl save its pennies for a "perfect" SPUI rather than doing a "good enough" DII (or three) much sooner?

I drive the two in Georgia several times a week, and I love 'em.

[US71]

I've driven through the DDIs in Joplin and Springfield. 

The one in Joplin needs better signage.  And the cloverleaf that was there is not missed. 

My sister drove the MO 13/US 60 DDI today and hated it. I had to attempt to explain how it worked (like protected lefts), but she didn't understand it.

[apeman33]

My roommate expressed her displeasure with the Range Line DDI and agreed that it's poorly signed. She doesn't like switching sides of the road but could deal with it if it had, in her opinion, better signs.

[US71]

My roommate expressed her displeasure with the Range Line DDI and agreed that it's poorly signed. She doesn't like switching sides of the road but could deal with it if it had, in her opinion, better signs.

It feels a bit claustrophobic to me.

[Stratuscaster]

They're putting one in near me in Warrenville/Naperville, IL - at I-88 and IL-59. I've looked at the plans, and the signage seems a bit confusing from a drivers' point of view (but perhaps not from a MUTCD or roadgeek view).

I've driven thru some DDIs - and agree that often it's the signage that's the issue.

[US71]

They're putting one in near me in Warrenville/Naperville, IL - at I-88 and IL-59. I've looked at the plans, and the signage seems a bit confusing from a drivers' point of view (but perhaps not from a MUTCD or roadgeek view).

I've driven thru some DDIs - and agree that often it's the signage that's the issue.

Springfield, MO has 4 now. 2 are on MO 13

[skluth]

We have two near St Louis: I-270@Dorsett in St Louis County and I-70@Mid Rivers Mall Drive. I think they're great and very useful at interchanges where most of the traffic is entering/exiting the highway. Probably not as useful if the interchange is at a road with lots of through traffic. I am hoping they do more in the area and am encouraged by the post stating that they are relatively easy to retrofit.

Once you go through it you should have no problem navigating one again. If anyone finds it confusing, chances are they find a lot of driving confusing and the problem is behind the wheel.