: The diverging diamond interchange comes to St Louis. We're all going to die.

10-18-10, 02:52 AM

Summary: When driving under the highway, motorists switch to the opposite side of traffic. In theory, this would effectively reduce congestion making it easier to merge on and off. The problem is that I don't trust my fellow motorists to figure it out.

The motorists here:
I grew up in Belleville IL with a large roundabout in the town square, and people understood how to use it because it was in the middle of downtown, but when I see them appear in the rest of the STL metro area, especially in the suburbs, I worry. Some drivers believe that traffic already in the circle doesn't have the right of way, or that they can enter the circle without checking for traffic.

I'm going to check out this new interchange tonight or tomorrow.

10-18-10, 08:35 AM
There is a DD interchange at I-44 and one of the exits in Springfield. It takes some getting used to. There will definitely be carnage...

10-18-10, 08:54 AM
The design is horrible. Theoretically it's efficient, but in the real world, it doesn't work out. In the US, anyone gets confused when you are dealing with a design in which you have to keep to the left to exit, enter, or anything else. It's unnatural. Right now, Milwaukee is going through an extensive rebuilding process of all of it's interchanges and ramps on I-94 to eliminate garbage like this.

The other problem with this design is that it's not expandable. If traffic volume grows in the next 20 years and this interchange becomes overloaded, the only option is to rip the whole thing down, bridge included, and start over.

Usually designs like this are chosen because either the municipality's budget or lack of real estate around the interchange restricts them from choosing the better design, like using flyovers which are more expensive to build and take up more space, but allow seamless entering/exiting from the right.

10-18-10, 11:05 AM
This intersection is not big enough to warrant a flyover. Once people get used to it, it should work OK, but there will be a steep learning curve.

10-18-10, 12:07 PM
there's a similar style overpass/exchange back home in Concord NH - but there's no median ... i guess the intersection isn't as wide so you're only traveling on the wrong side as you're turning left to get onto the on-ramps

10-18-10, 01:36 PM
Just wait till some urban planner gets the wise idea to try and put a round about in the center of one of these diverging diamonds. Where I went to school they stuck a massive traffic circle right inbetween 2 stop lights then wondered why everyone hated it....now to give them a slight bit of credit the stop lights were on the plan to remove....but like 2-3 years after the round about was installed.

10-18-10, 02:25 PM
Sorry, double post

10-18-10, 02:25 PM
That idea was tried and deemed "too dangerous" in L.A. thirty-five years ago! I take the Missouri Highway dept. is dending their people to the same graduate school as Virginia's VDOT, with the same, incompetent, disastrous results. Hell, Virginia's VDOT couldn't even figure out how to spend fedral money .... how incompetent is that!

10-18-10, 05:06 PM
I use one of these every day. It isn't really that difficult. It's weird at first, but not hard at all to grasp. Here's a google maps version of what I deal with:


EDIT: Look at that kick ass awesome on-ramp for 9A. You've gotta love Florida. :lol:

10-18-10, 05:18 PM
Sheesh! That arrangement is just asking for trouble. What's wrong with a regular diamond interchange? There are plenty of them at the busiest freeway-surface street interchanges in Phoenix as well as one I use frequently in Salem:


They handle heavy traffic just fine.

10-18-10, 08:04 PM
Here is the one in Springfield that the one in St. Louis is patterned after.

They do actually work very well.


10-19-10, 02:27 AM
I'll wait till the dust clearz. St Louisans can't drive to begin with. And now you want to confuse them with wrong way traffic flow. Hell the last two wrong way fatalities in the city were COPS!

10-19-10, 03:34 AM

Looks better in person. They used tall concrete curbs and walls to make it inconvenient to turn into oncoming traffic. When the directions switch, the turns are so sharp that it looks like a T intersection, encouraging the driver to go through the intersection to the other side rather than making a 90-degree right.