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.
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.
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.