By: Contech Engineered Solutions
Project Summary
ALDOT used 3,479 feet of corrugated steel slotted drain to manage surface runoff during an I-85 widening project in Opelika, Alabama. The system captures sheet flow within the median while supporting highway safety and future roadway expansion.
Managing Surface Runoff During a Major I-85 Widening
Highway widening projects create challenges both above and below the pavement.
For the Alabama Department of Transportation, widening Interstate 85 near Opelika meant accommodating growing traffic demands. The project also included a new median barrier wall designed to help prevent crossover accidents.
However, the new roadway configuration created another important consideration: surface runoff.
ALDOT needed to capture sheet flow in lower portions of the crossover. Otherwise, water could collect on the pavement and increase hydroplaning risks. At the same time, crews needed to maintain traffic flow during construction.
The solution placed a corrugated steel slotted drain system directly within the center median.
The project demonstrates how slotted drain pipe can integrate surface drainage into heavily traveled paved areas. It also shows how drainage design can support larger transportation safety improvements.
3,479 Feet of Corrugated Steel Slotted Drain
The I-85 widening project incorporated 3,479 linear feet of 24-inch galvanized corrugated steel pipe. Variable-height grates ranged from 12 to 18 inches.
Contech Engineered Solutions fabricated the system and submitted the project to NCSPA. ALDOT served as both owner and engineer.
The variable-height configuration allowed the system to capture runoff while ALDOT optimized the pipe slope for improved hydraulic performance.
This flexibility matters in highway drainage.
Surface elevations do not always provide the slope needed below ground. Variable-height slotted drain lets designers address that difference while maintaining the desired surface inlet elevation.
Engineers working through similar drainage challenges can find additional hydraulic and structural guidance in NCSPA’s corrugated steel design resources. NCSPA also maintains broader technical resources covering CSP design, installation and long-term performance.
Designing the I-85 Drainage System for Highway Loads
The location presented a demanding structural environment.
The slotted drain needed to withstand repeated impacts under HS20 loading conditions. Therefore, the project used heavy-duty components to strengthen the system.
Crews welded shear studs to the sides of the grates. They then encapsulated the system with 750 psi flowable fill concrete.
That construction detail helped reinforce the drainage system within an active interstate environment.
Installation began by trenching and grading the ditch bottom in the median. Crews then placed the slotted drain before completing the flowable fill backfill.
The result is easy to overlook in the completed project photos. Only the narrow continuous inlet remains visible along much of the median.
Below that opening, however, the 24-inch corrugated steel pipe carries captured runoff away from the roadway.
Reducing Sheet Flow and Hydroplaning Risk
Surface drainage has a direct relationship with highway safety.
The I-85 system was specifically designed to collect sheet flow in lower areas of the crossover. By intercepting runoff, the system reduces water flowing across or collecting on the roadway.
That helps address one of ALDOT’s primary concerns: hydroplaning.
The approach closely parallels an older NCSPA project involving ARDOT’s I-430 and Highway 10 drainage improvements. There, engineers also used corrugated steel slotted drain to intercept hazardous roadway sheet flow while minimizing traffic impacts.
A similar approach appeared in the Highway 50 Camino Safety Project. That highway improvement incorporated more than 5,100 feet of slotted drain alongside roadway widening and median safety improvements.
Together, these projects demonstrate the role drainage can play in broader highway safety improvements.
Keeping Traffic Moving During Construction
Drainage was only one part of ALDOT’s challenge.
I-85 remained an active transportation corridor throughout construction. Therefore, maintaining traffic flow influenced how the project moved forward.
ALDOT used a crossover construction method that allowed vehicles to continue moving through the corridor during the work. The approach minimized traffic disruption while crews completed the widening and drainage improvements.
That construction efficiency is especially important for DOT projects, where closures and detours can create impacts far beyond the work zone.
It is also one reason adaptable steel infrastructure can provide value on transportation projects. NCSPA’s Why Steel resources highlight installation flexibility and reduced traffic disruption among the advantages of corrugated steel systems.
Building Capacity for the Future
The completed project addresses an immediate drainage need while supporting ALDOT’s larger transportation goals.
Widening I-85 helps accommodate increasing traffic through the Opelika area. The improvements also provide capacity for additional lanes in the future as regional transportation demands continue growing.
Meanwhile, the median drainage system helps protect that investment by moving surface runoff away from the traveled roadway.
For ALDOT, the project combines highway expansion, median safety improvements and stormwater management within one coordinated effort.
What appears from the roadway as a narrow opening in the pavement represents 3,479 feet of purpose-built corrugated steel drainage infrastructure underneath.
And on a busy interstate, sometimes the best drainage solution is the one motorists barely notice.