The heavy hauls along Route 15 have ended.

While most of us were sleeping, hundreds of tons of heavy machinery have been rumbling slowly through Prince William and Loudoun counties and across the southern edge of Leesburg. The hauls — 36 in all over the past five months — have been delivering bulky components for the Panda Stonewall power plant that is being constructed off Sycolin Road at Goose Creek.

Bechtel is building the Stonewall Energy Center in partnership with Siemens for Panda Power Funds, the Dallas-based owner of the plant, Bechtel spokeswoman Jane Griffin said.

The project has been billed as a “clean energy” plant, fueled by natural gas with advanced emissions control technology, and using reclaimed water from the town of Leesburg to cool the boilers. The plant is being built near existing power lines, Griffin said.

After the plant becomes operational in May 2017, it will supply enough power for 778,000 homes at peak capacity, said Andy Gillespie, the project manager and an engineer for Bechtel.

The hauling was overnight, between 10 p.m. and 5 a.m., to minimize the disruption to traffic, Gillespie said.

There was little evidence that the hauls were taking place at the time, except for signs flashing warnings of impending road closures and detours, and streams of email and text alerts from the Loudoun County Sheriff’s Office updating the progress of each haul.

The transports started in Gainesville, where the heavy components — gas and steam turbines, boiler modules, transformers and generators — were carefully lifted off rail cars. Edwards Moving & Rigging hauled them along a 29-mile course, north on Route 15, then to Battlefield Parkway in Leesburg, across the Dulles Greenway and onto Sycolin Road.

The size and weight of the components posed a significant challenge. The bulkiest were the 24 boiler modules, each weighing about 200 tons and stretching 120 feet in length — the height of a seven-story building when upright, Gillespie said. The heaviest were the generators, weighing more than 280 tons, he said.

“This took a year and a half of planning, to get all of these modules here,” Gillespie said. “When you build a project like this, our job is [to] manage risks. And we knew this was essentially a risk. Heavy haul always is.”

During the planning phase, the project’s managers coordinated with the Virginia Department of Transportation to make sure every bridge and roadway could support the loads. Traffic signals had to be raised at some intersections to make way for the boiler modules, which are 19 feet high even when horizontal, Gillespie said.

For most of the hauls, a truck pulled the load on a Goldhofer transporter — a flatbed trailer with 144 wheels, 18 from front to back and eight across. Another truck pushed from behind.

Moving the generators required two trucks pulling and two more pushing from behind. To disperse the weight, the generator was positioned on a girder supported by two Goldhofers, Gillespie said. Those hauls crept so slowly that they took place over two nights, stopping midway at Gilberts Corner in Aldie.

The project managers devised a procedure Gillespie called “crabbing” to move the heaviest hauls across the bridge over Interstate 66. So that all the weight would not be on one side of the bridge, the two Goldhofers were maneuvered across the bridge, with one on each side of the center median and the girder bearing the generator crossing diagonally between them.

During each haul, a VDOT crew removed street signs where necessary to make way for the behemoths, and a second crew trailing the haul replaced them, Gillespie said.

In an interview on March 16, before the last two hauls, Gillespie said he was looking forward to the end of the hauling process.

“It’s a feeling of great satisfaction, because there’s just so much effort,” he said. “So [after] a year and a half of planning, there’s nothing quite like when the plan has come together.”

Gillespie said that he received progress reports via text messages throughout each haul, and was always relieved when the last one came, usually about 4 a.m., notifying him that the load arrived safely.

Early Friday morning, he received the last text. The generator had arrived.