Case Study: I-5 Skagit River Bridge Collapse During Construction (Washington, 2013)

Project Overview
• Name: I-5 Skagit River Bridge Replacement and Repair
• Location: Skagit County, Washington
• Year: 2013 (May)
• Project Size: $30 million repair project
• Scope: Partial replacement and repair of an aging steel truss bridge on I-5
• Lead Agencies/Contractors: Washington State DOT /

Category of the Issue, Problem, or Challenge
• Structural Failure
• Load Management

Summary of the Issue, Problem, or Challenge
During repair operations, an oversized load transported by a truck struck two critical steel girders, causing a partial collapse of the bridge span onto the river below. The collapse occurred during active traffic control and repair, disrupting a major highway route.

Root Cause Analysis

  • Oversized Load Clearance Miscalculation: The height and width of the transport were underestimated.
  • Inadequate Temporary Protection: No physical barriers or guard rails to prevent impact on structural elements.
  • Communication Gaps: Insufficient coordination between transport team and bridge repair crews.
  • Aging Structure: The bridge had limited redundancy, so impact led to disproportionate failure.

Impacts Due to the Issue, Problem, or Challenge

  • Immediate closure of I-5, disrupting regional transportation.
  • Emergency repairs costing tens of millions and long traffic delays.
  • Increased scrutiny on load permitting processes.

Corrective Actions Taken

  1. Revision of oversized load permitting, requiring strict route surveys and pre-clearance.
  2. Installation of temporary protective barriers during repair operations.
  3. Improved communication protocols between transport agencies and construction teams.
  4. Accelerated bridge inspection programs for other similar aging infrastructure.

Lessons Learned

  • Impact hazards during repair operations must be proactively mitigated.
  • Coordination between transport and construction teams is critical.
  • Temporary protection systems can prevent damage from accidental impacts.

Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation

  • Are routes for oversized loads surveyed and clearance verified with current construction activities?
  • Are temporary protective barriers installed around vulnerable structures during repair?
  • Is communication protocol established for coordination between transport and construction teams?
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