By: Contech Engineered Solutions
Project Summary
The 2024 NCSPA ALT2 Coating Project of the Year improved drainage along a major Interstate 35 widening project in Iowa. The slotted drain system helps manage roadway runoff, protect infrastructure investments, and improve driving conditions for motorists.
Supporting a Major Interstate Improvement Project
As traffic volumes continued to increase along Interstate 35, the Iowa Department of Transportation initiated a major infrastructure improvement effort designed to expand capacity and improve safety.
The project included bridge construction and the widening of an eight-mile section of Interstate 35 from two lanes to three lanes in each direction. Beyond increasing capacity, the improvements were intended to enhance traffic flow, reduce congestion, and improve overall roadway performance for daily commuters.
Like many major highway projects, the roadway expansion created new drainage challenges that required careful planning and long-term solutions.
Submitted by Contech Engineered Solutions, the project earned recognition as the 2024 NCSPA ALT2 Coating Project of the Year for its innovative approach to highway drainage and surface water management.
Managing Surface Water Along Interstate 35
Roadway widening often changes drainage patterns and increases the amount of paved surface area that must be managed during rain events.
Along Interstate 35, extensive grading, resurfacing, and roadway reconstruction created a need for an effective drainage system capable of capturing and conveying runoff before it could impact traffic operations or roadway performance.
To address these challenges, engineers selected a slotted drain pipe system designed to efficiently collect surface water while integrating directly into the roadway infrastructure.
Transportation agencies evaluating similar drainage applications can explore NCSPA’s Technical Resources and Design Data Sheets for additional drainage design guidance.
Slotted Drain System Provides Efficient Performance
The completed system included approximately 6,444 linear feet of 36-inch diameter slotted drain pipe equipped with 6-inch grates.
Manufactured in Iowa, the system was delivered and installed efficiently within the project corridor. The six-inch grate configuration met AASHTO H-20 loading requirements while providing the durability needed for long-term highway service.
Slotted drain systems continue to be an effective option for transportation infrastructure projects because they capture runoff directly at the pavement surface while minimizing maintenance requirements and preserving valuable roadway space.
The system’s performance characteristics made it particularly well suited for the Interstate 35 project, where reliable drainage was essential to maintaining roadway safety and protecting the investment in the expanded corridor.
Built for Long-Term Highway Performance
Highway drainage systems must withstand demanding conditions throughout their service life.
In addition to managing runoff during storm events, drainage infrastructure must accommodate traffic loads, temperature fluctuations, and long-term environmental exposure. Engineers designed the Interstate 35 drainage system to perform under these conditions while supporting the long-term goals of the roadway improvement project.
The use of ALT2-coated slotted drain pipe provided durability and corrosion resistance appropriate for a major transportation corridor. Agencies evaluating service life considerations can utilize NCSPA’s Service Life Calculator and review additional research available through NCSPA’s Studies & Reports.
A Proven Solution for Transportation Infrastructure
The Iowa DOT’s previous experience with similar drainage applications helped support the decision to utilize a slotted drain pipe system on Interstate 35.
That confidence, combined with efficient installation and strong long-term performance expectations, contributed to the project’s success. The completed drainage system now helps manage surface water, improve roadway conditions, and support safer travel for motorists throughout the corridor.
The Interstate 35 project demonstrates how properly designed drainage infrastructure can play a critical role in the success of large-scale transportation improvements while helping agencies protect roadway investments for decades to come.