Diverging Diamond Interchange

Opportunities for Improvement

Interstate 35 serves as a primary transportation corridor connecting Iowa with other locations throughout the Midwest. At the time of its construction in 1965, the population of Ankeny, Iowa was just over 1,000 people.

Today, Ankeny is one of the fastest growing cities in the nation. Ankeny has doubled its population from 27,117 people in 2010 to over 55,000 people in 2016.

Increased traffic that accompanies the area’s growing population, along with residential and commercial development, has led to an increase of traffic congestion and severe crashes near the E. 1st Street Interchange.

A study completed by the Iowa DOT and the City of Ankeny proposed the following improvements:

  • Construction of a Diverging Diamond Interchange (DDI) at the E. 1st Street Interchange
  • Widening of I-35 from six to eight lanes from Oralabor Road to East 1st Street
  • Widening of I-35 from four to six lanes from E. 1st Street to NE 36th Street
  • Widening E. 1st Street to five lanes from Delaware Avenue to Frisk Drive to accommodate the Diverging Diamond configuration and provide additional capacity for continued growth in Ankeny
  • Reconstruction of two I-35 bridges over Four Mile Creek, two I-35 bridges over E. 1st Street, and the widening and overlay of the E. 1st Street bridge over Four Mile Creek east of I-35

Increasing Safety & Efficiency

A DDI was chosen over other alternatives for its ability to safely and efficiently move large volumes of traffic while minimizing its footprint on the surrounding area. Construction began in 2017 and is expected to conclude 2020, making the E. 1st Street DDI the second of its kind in the state of Iowa. During construction, a detailed staging design will allow continuous traffic movement while maintaining the safety of the public and contractors.

An Environmental Assessment completed in October 2015 concluded the project is necessary for safe and efficient travel with no significant social, economic or environmental impacts that would warrant an environmental impact statement. Due to the fact that Four Mile Creek is a sensitive urban stream, culverts and bridges are designed in accordance with DNR and DOT requirements to reduce upstream flooding.

Snyder & Associates serves as the primary design consultant for roadway and ramp improvements, with Shuck-Britson, Inc. as the lead structural designer for bridges and box culverts. Snyder & Associates will also facilitate coordination with utility owners and develop the required platting and permits. Terracon, Inc. will complete all geotechnical engineering.