For drivers heading in and out of the South Hills in August 2013, the daily commute was trying at times. Construction on the 5,888-foot-long Liberty Tunnel prompted 24-hour closures of first the outbound side, then the inbound.

That meant detours.

And while commuters making their way around the tunnel closures likely saw workers on the north and south ends of the tunnel restoring concrete facades, much of the work inside the tubes went unseen.

Working two 12-hour shifts a day, crews inside the tunnel resurfaced walls, made electrical upgrades and reconstructed the ventilation arch wall, which circulates air into the tunnel. Roughly 100 workers were involved in the day-to-day construction efforts during the closure period.