• J.L. Patterson & Associates, Inc.

    Cascade Tunnel Study

    Stevens Pass, Washington, United States

Project Summary


The Cascade Tunnel, the longest railroad tunnel in the United States, near Stevens Pass, Washington, is a vital corridor for shipping cargo from Pacific Rim countries to the United States. BNSF Railway retained J.L. Patterson & Associates to survey and model the tunnel for re-alignment and clearance envelope improvements. However, the highly utilized corridor allowed just 1-2 hours of tunnel access at a time.


With these access constraints, it would have taken weeks using conventional survey methods to model the interior of the tunnel. Instead, J.L. Patterson & Associates combined control and LiDAR survey techniques to analyze the existing alignment of the track inside the tunnel and model the tunnel’s interior surface using MicroStation and its powerful point-cloud management tools. Using Bentley products and LiDAR technology, J.L. Patterson & Associates modeled the 7.8 mile tunnel including both the track and notch alignments in the tunnel roof created in 1989 to allow double stack intermodal trains to operate.


Bentley solutions were pivotal in saving time and money by reducing the amount of cut, improving operations, and minimizing disruptions to the line. Without track realignment, the cut would have been 177 cubic yards and cost USD 10 million. Calculating the realignment using powerful regression models in Bentley software reduced the cut to 8.3 cubic yards, thereby reducing construction duration and cutting costs by 90% to USD 1 million.


Using Bentley software to minimize work in the field helped avoid expensive excavations inside a highly trafficked tunnel. The LiDAR technology and Bentley Pointools helped to achieve the objective of designing the tunnel clearance for container traffic at one-tenth the cost.
  • The survey team established horizontal and vertical survey controls at each portal and control targets along the tunnel at 1,500-foot spacings.
  • Control points and inertial navigation data were used to determine the best estimate trajectory of the mobile mapping system’s 3D route.
  • Point cloud data from the LiDAR sensor, which traversed the tunnel on a specially equipped high-rail vehicle, allowed J.L. Patterson & Associates to develop a digital 3D model of the tunnel's internal surface, tracks and notch alignments.
User Quote:
  • "As engineers we are frequently tasked with solving complex challenges that inevitably have significant safety, fiscal, and schedule impacts. Bentley has always been there for us to use as a component of our engineering toolbox."

    Marc Cañas Vice President J.L. Patterson & Associates, Inc.