The initial Gravelly-Thorne Connector proposal included one motor vehicle lane and a shared-use path, to be built in stage 4 of the overall I-5 - Mounts Road to Thorne Lane I/C - Corridor Improvements project.
In the second phase of construction during the overall project, the design-build contractor, Guy F. Atkinson Construction, included in their design a new auxiliary lane to southbound I-5 between Gravelly Lake Drive and Thorne Lane. This new auxiliary lane provides capacity for traffic entering southbound I-5 at Gravelly Lake Drive and exiting at Thorne Lane or Berkeley Street. Based on traffic analysis, this new addition to the design in stage 2 construction will replace the motor-vehicle lane that was initially included in the Gravelly-Thorne Connector proposal.
As of July 2019, the new Gravelly-Thorne Connector proposed design now consists of a non-motorized shared use path. The shared use path will provide a much needed pedestrian and bicycle connection to and from Tillicum without having users trespass on to Sound Transit railroad right-of-way or use the shoulder of I-5. The shared use path will be built so emergency vehicles can use the path as an alternative to I-5 if needed.
Initially included in stage 4 construction was a proposed bicycle and pedestrian path between Lakewood and DuPont, providing a multi-modal option for travel beyond the Gravelly-Thorne Connector project.
A stakeholder engagement process evaluated options and determined that a Shared-Use Path alignment through Lewis North (parallel to roads open to the public) would best meet this need. The shared use path between Lakewood and DuPont will be addressed in a future project, separate from the Gravelly-Thorne Connector project.
In July 2015, the Washington State Legislature included $495 million to fund the I-5 Mounts Road to Thorne Lane Interchange - Corridor Improvements project, as part of the Connecting Washington transportation package. This project is funded through a 10 year period, from 2015-2025.
Gravelly-Thorne Connector estimated costs for engineering, right-of-way and construction total $21.5 Million.