Indiana State Road 431

Infobox road
state=IN
type=IN
route=431
alternate_name=Keystone Ave
length_mi=5.7
length_round=1
length_ref= [http://illi-indi.com/EndsPage.php?id=1431&section=1 Indiana Highway Ends - SR 431] ]
established=
direction_a=South
starting_terminus=
junction=
direction_b=North
ending_terminus=
counties=Hamilton, Marion
previous_type=IN
previous_route=427
next_type=IN
next_route=441

The former State Road 431, now simply Keystone Avenue remains a busy route connecting U.S. Route 31 with Interstate 465 at Exit 33. It passes through the Indianapolis suburb of Carmel, allowing traffic on U.S. 31 north of Carmel a shorter route to I-465 and the east side of Indianapolis. Until the 1990s, the State Road 431 designation extended south of I-465 to 86th Street. Prior to that, it also continued south along N. Keystone Avenue to S.R. 37 at Fall Creek Parkway, North Drive in Indianapolis.

State Road 431 was officially decomissioned on October 19, 2007, with the portions north of 96th Street being turned over to Hamilton County highway officials. Carmel Mayor James Brainard immediately proposed banning heavy trucks from the route, the Hamilton County portions of which lies within his city's corporate limits. He has also pushed for a plan to build six roundabout-style interchanges on Keystone in lieu of widening it to at least six travel lanes throughout.

Further south in Marion County, a former southern portion of S.R. 431 extended south along Madison Avenue from the south side of Indianapolis through Greenwood. Madison Avenue, which was the original routing of U.S. 31 on Indy's south side, does not have an interchange with I-465, however. The northern terminus of this section was at Madison's intersection with East Street, which used to carry U.S. 31 to the south. The southern terminus was where Madison merges with existing U.S. 31 alignment in Johnson County just south of Smith Valley Road, south of Greenwood Middle School.

References