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February 6, 2023
David Evans and Associates
Project: Downtown Seattle Transit Tunnel
Client: Sound Transit
The Downtown Seattle Transit Tunnel provided a valuable transit solution through the heart of downtown Seattle for over 20 years, carrying bus traffic through the 1.3-mile-long twin-bore tunnel with four passenger stations. When Sound Transit assumed ownership of the DSTT, it first needed to document the ownership rights and prepare for the numerous improvements to the facility to transition the bus tunnel to carry light rail trains and improve public access and safety.
To help accomplish this monumental task, Sound Transit created the DSTT State of Good Repair Program and enlisted the expertise of David Evans and Associates, under contract to WSP, with management support from KPFF, to survey the facilities and prepare the necessary documentation.
The three-dimensional elements of the ownership rights and improvement plans required an innovative solution to create a detailed conditions survey. The field surveying would occur while the facility remained fully operational, adding to this project’s complexity.
The David Evans Associates team applied innovative 3D laser scanning (LiDAR) and 360-degree digital photography to document the existing conditions, combined with traditional land surveying, for survey control and boundary monuments. This combination emerged as the most thorough, accurate, and efficient way to complete the field surveys.
The existing conditions survey was created using state-of-the-art 3D laser scanning technology to gather highly accurate and detailed pointcloud (LiDAR) data throughout the twin bores, the four stations, and the surface entrances to the underground facilities. The resulting 3D model featured colossal scale and detail and was used as the sole source of truth by the owner and supports design modifications, operations, maintenance, security and safety.
The second essential tool DEA developed was an interactive web map created from 360-degree digital photography, providing virtual views of the entire facility from any internet-connected device. These highly detailed representations of the facility’s as-built conditions also facilitated more efficient operations and maintenance work without the constraints of track access permits.
This highly complex and unique project will benefit the public for many years. The existing conditions (BIM) will simplify future improvement designs, operations, maintenance, security and safety. Ensuring that Sound Transit has all the ownership and access rights necessary for the tunnels and stations is vital to protecting the public rights to this valuable public asset.