Roundabouts are OUT and Diverging Diamonds are IN

Janesville residents were first introduced to the "modern" roundabout in 2007, one at the intersection of Sandhill Drive and Sandstone and the other on Morse Street off of Hwy 26 at the entrance of the new Menards development. Two more roundabouts were constructed in 2013 at the Racine Street on/off ramps with I-39/90. The roundabout was such a hot topic during construction that the City of Janesville posted a "Roundabouts" selection under Department and Services tab on their website in hopes of helping drivers navigate around the central island. 

While I've never personally been in or witnessed an accident in these areas, I can't deny that the roundabout provides a safer driving environment by reducing speeds and conflict points and allowing easier decision-making for drivers. So maybe the roundabout is everything they said it would be. 

Courtesy of http://www.mikeontraffic.com/

But what is a Diverging Diamond Intersection and will the City of Janesville soon be providing us with yet another selection under the Department and Services tab? The Wisconsin Department of Transportation already has.

The Diverging Diamond Interchange (DDI) is said to be a revolutionary design that transfers traffic to the opposite sides of the road for a short distance to allow vehicles to make direct turns onto the highway. Experts say diverging diamonds are safer than traditional highway ramps because they eliminate turns in front of oncoming vehicles. The DDI allows cars to enter the highway without turning in front of oncoming traffic. The design is said to improve the efficiency of an interchange. The diverging diamond design is more compact than other highway ramps, which means it requires less land and a smaller bridge and ramp system.

So, between now and 2021, Janesville residents and travelers all around will be introduced to the DDI at both I-39/90 and Hwy 26/Milton Avenue and I-39/90 and Hwy 11/Avalon Road. Although the definition of the DDI seems complicated and, at the very least, confusing, I assume that if I just concern myself with what is ahead of me instead of what is going on around me I'll be just fine, right? Below is a link showing an animation of both the I-39/90 and Wis 26 Diverging Diamond Interchange as well as the I-39/90 Wis 11 DDI. Check it out.



I-39/90 and Wis 26 (Milton Avenue) Diverging Diamond Interchange Animation


I-39/90 and Wis 11 (Avalon Road) Diverging Diamond Interchange Animation

The diverging diamond interchange was listed by Popular Science magazine as one of the best innovations in 2009 (engineering category) in "Best of What's New in 2009".