ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/319569
Carmel, Ind., is an affluent community to the north of Indianapolis and contains one of Indiana's largest b u s i n e s s d i s t r i c t s . I t h a s g ro w n substantially over the past 10 years, adding 50,000 residents. The explosive growth spurred many traffic challenges, with Carmel's most heavily traveled road—Keystone Avenue—growing increasingly sluggish and, as drivers tried to beat traffic lights, more dangerous. S i n c e t h e l a t e 1 9 6 0 s , K e y s t o n e Avenue, also known as Indiana State R o a d 4 3 1 a n d c o n t ro l l e d b y t h e Indiana Department of Transportation (INDOT), had been a four-lane, divided roadway with seven at-grade signalized intersections—two of which were rated as "failing" at peak travel periods, according to a state-led analysis. The c o r r i d o r, n o w re n a m e d K e y s t o n e Parkway, averaged 200 accidents each year. From planning gridlock to Fast track Seeking a minimally disruptive, long- term solution, City Engineer Michael McBride proposed to introduce grade separations at intersections using teardrop roundabouts. Meanwhile, Carmel Mayor Jim Brainard asked the state to relinquish control of the corridor—a request the city had been making for more than a decade. Taking their cue from "Major Moves"— an aggressive program by Indiana Governor Mitch Daniels calling for much faster execution of road and bridge projects—the state agreed that Carmel was in a better position to meet the deadlines. Keystone Avenue was turned over to Carmel, which then partnered with American Structurepoint Inc. to refine and implement its plan. Driven to teardrops As the engineers began shaping the design, it was clear roundabouts would be key ingredients to the solution, and with good reason. Studies point to roundabouts as one of the safest, most efficient intersection control techniques. Not only do accidents occur less frequently, but the severity of accidents at roundabouts is far less than stop- controlled or signalized intersections. "Anytime you remove conflict points, you improve safety," McBride explained. "A two-lane, four-way signalized intersection has more than 30 conflict points," he added, "but a typical single- lane roundabout has only eight." As the design progressed, a unique teardrop interchange configuration— the tightest in the nation—emerged as the silver bullet. When measured center to center of the teardrop, the ramp termini are less than 290 ft apart, with profile KEYSTONE PARKWAY INTERCHANGES–106TH AND 126TH STREET BRIDGES / cARMEl, INDIANA BrIDge DesIgn engIneer: American Structurepoint Inc., Indianapolis, Ind. prIme contrActor: Milestone contractors lP, Indianapolis, Ind. concrete suppLIer: Irving Materials Inc., Greenfield, Ind. gIrDer precAster: Prestress Services Industries llc, lexington, Ky., a PcI-certified producer BrIDge constructIon cost: $3,081,160 (without MSE walls and approaches) Superstructure and deck $76.01/ft 2 ; Substructure $39.78/ft 2 by David A. Day and Andrea B. Emerson, American Structurepoint Inc. Bridging the gap the nation's Most Compact double-teardrop interchange Keystone Parkway's teardrop interchange configuration is the tightest in the nation. This is the 106th Street Bridge. All photos: American Structurepoint Inc. 24 | ASPIRE, Fall 2010 ASP10-1704.indb 24 9/17/10 2:05 PM