First Avenue Grade Separation

First Avenue is a main north-south arterial roadway in Iowa City, Iowa. Each day, approximately 13,000 vehicles utilize the corridor, and future volume is anticipated to increase.  In addition, there is notable pedestrian and bicycle traffic in the area due to a mix of development that includes South East Junior High School.

On average, between two and four trains block First Avenue per day, causing conflicts, major traffic delays, and safety concerns for vehicles and pedestrians.

Prior traffic studies were completed and reported an average wait time of 10 to 20 minutes for idle vehicles while the crossing was blocked. Traffic that chose to explore alternative routes was detoured at least four miles to the nearest grade-separation crossing at Summit Street.

To improve traffic flow and safety, Snyder & Associates, Inc. developed a plan which lowered First Avenue approximately 16.5’ and raised the Iowa Interstate Railroad (IAIS) 5′ to create a grade separation crossing. 

The City of Iowa City designated funds, along with support from federal funding, to design and construct the separation between the railroad and vehicle and pedestrian traffic. A new railroad bridge, street paving, retaining wall, storm sewer, water main, and other related work were included in the project.  The existing four-lane arterial roadway was reconstructed as a three-lane section with a bike lane in each direction.  Significant retaining walls were constructed to provide an opportunity to implement aesthetic elements into the project which included a decorative form liner, stain, and aluminum railing.

Construction consisted of five main stages beginning in April 2015 and concluded in fall 2016:

Stage 1 – Water main, storm sewer, onsite detour roadway, and railroad shoofly construction.

Stage 2 – Critical closure to complete onsite detour roadway and railroad shoofly construction.

Stage 3 – Retaining wall, bridge abutements and wingwalls, mass grading and paving, and new north (IAIS) railroad construction.

Stage 4 – Completion of mainline paving and junior high paving along with a critical closure to connect the new north (IAIS) railroad across the onsite detour roadway.

Stage 5 – Completion of the retaining wall, side path, and parking lot construction.

Key components contributed by Snyder & Associates, Inc.:

  • Unique project design with significant change in grade and infrastructure construction required within a fully developed area and with no direct impact on existing structures.
  • Keeping both transportation corridors open to the fullest extent was a primary goal during construction, so the Snyder team designed an onsite detour roadway to maintain at least one lane of traffic while providing a large work area for construction to occur.
  • A shoofly railroad track was designed to maintain unimpeded service for the (IAIS) Railroad.
  • During design, the need for a storm sewer pumping station was eliminated by finding a means of gravity draining the project. This resulted in significant cost savings in terms of construction and ongoing maintenance.