Highways for Habitats #8: Keystone Parkway Roundabouts

Keystone Parkway CroppedTransportation planning is tough.  Roads have to serve a number of (sometimes competing) purposes.  Roads whose primary purpose is moving people and goods quickly through a community often have a detrimental effect on the communities they bisect (see: the history of freeways in Detroit).  Take state trunk lines for example, which you can recognize because they’re usually twice as wide to cross as the other roads in a neighborhood, and, of course, highways and interstates.  We’re currently running a series of posts featuring creative solutions from around the globe to make these roads – roads that must run through communities – also work to serve those communities.  Check out more about our inspiration here.

Indiana State Road 431 was decommissioned in 2007, and became the Keystone Parkway when Carmel, a suburb of Indianapolis, took ownership.  At nearly 20 miles long it connects I-465 and US-31, both major travel routes.  As the suburb grew, and with it traffic congestion, the Indiana Department of Transportation proposed to widen the highway with diamond interchanges as a solution, but Carmel saw this as a temporary solution that ignored local traffic patterns and required the destruction of a number of buildings.  Carmel chose instead to move forward with what it knew best – teardrop roundabout interchanges.

Teardrop roundabouts use one-third less area than traditional diamond interchanges, thereby preserving green space and potentially causing less damage to nearby neighborhoods.  They cost less to construct and maintain.  Removing stoplights keeps cars from idling (saving gas), improves traffic flow, reduces carbon emissions, and cuts back on noise.  Roundabouts are also proven to reduce the number of personal injury accidents at intersections – because they require constant attention and move traffic slower – by a whopping 78% (non-injury accidents by 37%).  To top of it all off, they look nicer, too.

Since 1997 Carmel has been swapping out traditional intersections – stoplights, stop signs and diamond interchanges – with roundabouts.  Residents appreciate the change, noting quicker travel times and gas money savings.  Carmel has plans to replace nearly all intersections with roundabouts, saving city money needed to light and maintain traditional intersection utilities.  Today Carmel is internationally recognized for its network of roundabouts, having more than any other U.S. city.  Michigan’s DOT has completed 13 roundabouts, and nationally we have around 3,000 (up 10% from 1997); we’d love to see that number continue to rise.


Photo from the.urbanophile on flickr.com