Steering Bertha is a challenge unlike any other. With no GPS available to steer the mammoth boring machine, engineers resort to a system of lasers to guide its movements.
Bertha has entered its home stretch, the last 1.7-mile trip north. The project which started in late 2013 has now completed 83% of the dig. The project has been an overall success so far with no need to inject any grout to reinforce buildings or streets. Bertha is expected to tunnel through some in the later part of May 2017.
This video was posted on youtube by wsdot.