Safety Improvements at 1st Street and State Street Intersection

The City of Ankeny was concerned with the safety at the 1st Street and NW State Street intersection and seeking safety improvements. The intersection was two four-lane undivided urban roadways with traffic signal control. Dedicated turn lanes did not exist on any of the four intersection approaches and visibility of left-turning traffic was obstructed by on-coming left-turn vehicle queues in the inside through lane.

The first step was reviewing the crash data which revealed that the intersection crash rate was above statewide averages. HR Green recommended that the City request a study through the Iowa DOT’s Traffic Engineering Assistance Program (TEAP). The City was successful in its request for TEAP funds and the study was completed through our on-call contract. HR Green completed the design and construction administration of the recommended capacity and signal improvements for the intersection and assisted in obtaining Iowa DOT funding for the construction improvements.

The intersection updates entailed widening, reconstruction, relocation, modification or adjustment of the following infrastructure within the above-described project limits:

1. PCC pavement surface and sub-base, driveways, sidewalks, pedestrian crossings, curb and gutter, parking lot
2. Traffic signs and pavement markings
3. Storm sewer piping and structures
4. Sanitary sewer manhole castings
5. Water valve boxes, service stops, hydrants
6. Traffic signals, including footings, supports, and interconnects
7. ADA sidewalk improvements
8. Street lighting layout

The safety improvements project evaluated the existing traffic patterns, traffic control, and lane use geometry to reduce visual obstructions and conflict points. Traffic control elements included temporary traffic control plans involving traffic signs, pavement markings, and signals to safely maintain corridor traffic throughout the construction stages.

Following the reconstruction, the intersection realized consistent reductions in crashes following the reconstruction while also incorporating ADA improvements, improved lighting, and signal improvements.