LOWER MACUNGIE TWP., Pa. -

It's been more than a year since Mack Trucks decided to shift its headquarters out of Allentown.

But Mack's manufacturing plant in Lower Macungie Township, Lehigh County is staying put and prospering.

You could say the one million square foot plant is the nuts and bolts of a building legacy lasting well over 100 years.

The plant has been building Mack Trucks since the 1970s. Sixteen months ago, Mack announced it was relocating its world headquarters from Allentown to North Carolina, but was keeping its local plant.

Last month, Mack shifted all production of its nine truck models to the facility, with 650 workers building 100 trucks each day. They are then shipped to more than 70 countries worldwide.

This October, 120 employees were brought back from layoffs, but the economy has taken a bite out of the bulldog.

Production is down 50 percent this year, however, an engine designed to leave air cleaner coming out than heading in is Mack's future.

The technology doesn't come cheap. Mack said hundreds of millions of dollars and countless hours have been spent to engineer what the company said is the cleanest truck on the road.