As project director on London’s $1.2-billion Silvertown highway tunnel, Juan Angel Martinez Diaz successfully adopted hovercraft-like skates to rotate the job’s 39-ft-dia tunneling shield to drive both bores of the 0.9-mile crossing, saving critical time on the project’s tight schedule.

After completing the southbound drive across the River Thames, the 1,600-ton shield was rotated in a pit on the south bank and launched with its train into the northbound drive. The whole operation lasted six weeks less than the 120 days allowed, says Martinez Diaz.