CASE STUDY
California I-40 Median Infill
Real-World Performance: MarMac® CSP Couplers in Action
San Bernardino County, CA
Apr-Nov 2021
105
CSP / CMP
This project stands as one of the largest single-site deployments of MarMac® CSP Couplers to date — a testament to the reliability of our coupling technology in major DOT stormwater infrastructure.
A safety-driven median regrading effort on one of California’s most remote interstate corridors demanded a drainage solution that was reliable, scalable, and fast to install. MarMac® Soil-Tight CSP Couplers delivered on every count — connecting and extending an existing corrugated steel pipe stormwater system across nearly 30 miles of high-desert freeway.
Project Overview
The California Department of Transportation (Caltrans) undertook the I-40 Median Infill project to address a significant safety hazard along a 29.6-mile stretch of Interstate 40 in rural San Bernardino County. The project corridor ran from approximately 4.5 miles east of Homer Wash bridge near the Town of Ludlow (Post Mile R125.0) westward to the California/Arizona State Line (Post Mile R154.6) — a remote stretch of high desert southeast near the City of Needles.
The existing median cross slopes within the 30-foot clear recovery zone (CRZ) ranged from 2:1 to as steep as 6:1 or greater — far exceeding safe highway design standards. Steep median cross slopes dramatically increase the risk of rollover collisions when vehicles leave the traveled way. To mitigate this hazard, Caltrans regraded the median to achieve slopes of 10:1 or flatter throughout the project corridor.
The substantial fill material required to bring the depressed median bed to grade with the freeway necessitated extensive modifications to existing drainage facilities within the median. This included the reconstruction and extension of existing offsite drainage facilities, specifically the extension of the corrugated steel pipe (CSP) storm drain network to maintain complete stormwater crossing beneath the roadway.
State of California
24-84" Diameter CMP / CSP
29.6 Miles
Installation Overview
1 Ease of Installation
The CSP Coupler’s external, band-style application allowed the contractor crews to work efficiently across a large, linear jobsite without requiring specialized equipment or extended installation time at each joint location.
2 Permanence
With the couplers buried beneath a regraded freeway median, long-term performance without maintenance was essential. CSP Couplers are engineered for permanent, in-ground service — providing lasting joint integrity even under dynamic loading and soil settlement conditions.
3 History of Performance
General contractor Ames Construction mobilized in April 2021 and completed the project in November 2021 — a seven-month construction window that encompassed both the median fill operations and the associated drainage work.
The drainage scope required extending existing CSP stormwater crossings beneath the roadway at multiple locations throughout the 29.6-mile corridor. At each location, MarMac® CSP Couplers were installed externally over the pipe joints, providing a soil-tight connection between the existing pipe sections and the newly installed extensions. The couplers’ corrugated profile engagement ensured a secure mechanical connection that resists axial separation and maintains alignment throughout the service life of the installation.
The project spanned portions of seven USGS 7.5-minute topographic quadrangles and crossed through multiple Ranges and Townships in unincorporated San Bernardino County — a logistically complex corridor in a remote, arid environment. The scalability and consistent field performance of the Soil-Tight Coupler were key enablers of on-schedule project completion.
Why MarMac® PolySeal Couplers
The Soil-Tight CSP Coupler delivered several critical performance advantages on this project:
Wide size range: Available from 6″ to 144″ in diameter, the Soil-Tight Coupler accommodated all 24″-84″ pipe sizes required across the project corridor — simplifying procurement and standardizing the installation process.
External application: The coupler installs over the outside of the pipe, eliminating the need to enter confined pipe sections and allowing rapid installation at each joint.
Soil-tight performance: Engineered to prevent soil intrusion at pipe joints, the coupler maintains the integrity of the stormwater conveyance system and protects the surrounding fill material from migration.
Durability in buried service: Designed for permanent underground installation, MarMac® CSP Couplers provide long-term joint performance consistent with the service life expectations of highway infrastructure.
Project Results & Performance
The I-40 Median Infill project was completed in November 2021, delivering a regraded median with slopes of 10:1 or flatter throughout the 29.6-mile corridor. By eliminating the steep, non-standard cross slopes that previously characterized the median, Caltrans significantly reduced the risk of rollover collisions — improving roadway safety for the thousands of travelers who use this stretch of I-40 each day.
The 105 MarMac® Soil-Tight CSP Couplers installed across the project corridor provide a permanent, maintenance-free solution for the extended stormwater drainage network — ensuring continued hydraulic performance beneath the newly regraded median for the long-term benefit of the traveling public.
