Friday, February 22nd, 2008

Carmel Roundabout Renderings Released

Carmel has released its designs and renderings for the roundabouts at 106th St. and 126th St. on Keystone Ave. Construction is supposed to start this spring. As previously reported, both of these are of modified dumbbell shape. However, both feature four lane, not two lane crossings of Keystone. That should reduce concerns over capacity. Here are some pictures.

106th St. looking northeast.

106th St. looking south

A view of the 106th St. underpass.

126th St.

There is also more on Carmel’s proposal for a roundabout at 96th St. and also the Keystone/I-465 interchange. INDOT’s current proposal shows a partial cloverleaf at this interchange, with traffic signals. I wrote in feedback on the project that had two primary points I thought needed to be re-examined. This interchange was one of them. Because traffic to the south is free flowing on Keystone, and traffic to the north will be free flowing when the roundabouts are complete, it makes no sense for the only traffic light within miles to be at an interstate interchange. (My other main point was to make I-465 a true ten lane section between I-69 and US 31. What Wingfield calls a ten lane road is actually an eight lane road with an auxiliary lane. I’d do ten lanes plus and auxiliary lane, otherwise this is a $650 million project to add only one lane – but that’s a pretty minor tweak – overall I was pretty pleased with the project design).

Carmel shares my view and has their own interchange design that would include flyover ramps. There is no rendering of this proposal or 96th St. available online. It would be nice if they uploaded it to their project web site (hint, hint). However, the impression I get is a fully free flowing ramp system. When I read flyover I read expensive. I’m not sure it is necessary to go that far. I think the primary goal should be to move through traffice without lights, not interstate bound traffic. Some type of three-level roundabout or “volleyball” interchange might accomplish this at lower cost.

I’ve linked to this before, but here is a picture of a three-level roundabout in Athens, Greece that even includes an integrated toll both system. Note the free flowing through traffic, the multi-lane roundabout, and the extreme ROW efficiency of this design.

[Image unfortunately deleted from Wikipedia]

Obviously an enhanced design would raise the price tag on the project. However, there may be some partially offsetting ROW savings if designed right.
Carmel wants to coordinate this interchange with construction at 96th St. It sounds to me like there is quite a bit of incremental money to be found for these projects, and Carmel and Indianapolis will no doubt need to contribute to the pot.

I said this before, but in many ways it is now Carmel that is the engine driving the region forward, not Indianapolis. Here we see an interchange well inside Indianapolis, but the Indy city government is absent while Carmel is aggressively fighting for something better. This is yet another example of what I’m talking about.

Topics: Transportation
Cities: Indianapolis

8 Responses to “Carmel Roundabout Renderings Released”

  1. CorrND says:

    I’m amazed by the aggressive timeline here. Fantastic leadership by Brainard/Carmel.

    I don’t know enough about interchange design to comment on the 465/96th design, but I definitely agree that Keystone has to be free-flowing. Can you point me to information about “volleyball” interchanges?

    I also note that on the 106th underpass view, they refer to the road as “Keystone Parkway.” I like that.

  2. The Urbanophile says:

    Search for “volleyball interchange” on Wikipedia

  3. Anonymous says:

    Where’s Carmel?

  4. thundermutt says:

    I don’t know that it’s necessarily “leadership” for Carmel or Ham. Co. to deal with 96th and Keystone…it’s a state-mandated obligation.

  5. The Urbanophile says:

    Carmel, Indiana, just north of Indianapolis.

    I was referring to leadership on the redesign of the Keystone/I-465 interchange.

  6. Crocodileguy says:

    I agree that the roundabout designs for US31 leave a lot to be desired. That firm has very little grasp on roundabouts as is, especially as evidenced by the geometries of the on/off ramps in relation to the roundabouts–as depicted, drivers would not be forced to slow down at all.

  7. Anonymous says:

    I live here in Carmel. I have to say it’s an awesome city. I really appreciate the eye for the future and sustainability that our city has. I was just reading your article and wanted to let you know that this years incoming freshmen class has over 1200 students. About 100 more than last years. Also, our total student population at the high school is just over 4000. Thanks for the cool blog! I’m excited to see how the roundabouts on keystone are going to turn out, as I live right by one of the construction sites!

  8. Anonymous says:

    Cool Roundabouts, I go to USI and we have a little one. I like the big ones though, they are way cooler.

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