With the most unsettling work done, all is calm at the world's busiest border crossing—the 40-acre San Ysidro Land Port of Entry, which is nearly four years into a three-phase $741-million transformation. Once worrisome, the incessant hum of the 50,000 vehicles that line up each day to cross into California from Mexico is now music to the ears of the members of the SYLPOE team, who, for three-plus years, had to keep more than 24 lanes of traffic moving 24/7 through an active jobsite.

The team is in a celebratory mood, having conquered the most grueling part of the decade-long overhaul: the $299-million first phase. The 46 new northbound vehicle-inspection booths, configured in tandem pairs, have slashed inspection wait times to 15 to 45 minutes from as long as four hours. The team also is celebrating the successful operation of the new non-potable-water, wastewater-treatment and energy systems that make SYLPOE the most self-sufficient border crossing anywhere.

Design work is gearing up for the $226-million second phase. Yet, already, the project is serving as a model for traveler-processing efficiency, security, safety and sustainability. "It's clearly the port of the future," says Anthony Kleppe, project manager for the owner, the Pacific Rim Region 9 of the U.S. General Services Administration.

Work at the 40-acre site—near San Diego, with Interstate 5 slicing through it—involved keeping 150,000 daily border crossers and port staff safe in a region the U.S. Dept. of Homeland Security recently ranked as the No. 4 top target for terrorists. Some 62 million vehicles and 137 million pedestrians crossed the jobsite since construction began in 2011.

"Every moment is crazy when you are working at the world's largest land port of entry and in the middle of a major freeway," says Jeffrey L. Wellenstein, project manager for Hensel Phelps (HP), manager of construction and general contractor for phase one, save a pedestrian bridge. "This was my hardest project ever."

At SYLPOE, DHS' U.S. Customs and Border Protection and other U.S. agencies process more than 50 million travelers annually, screening for terrorists, drug smugglers and undocumented travelers. By 2030, CBP projects that, each year, 85 million travelers will move from Tijuana into Southern California.

A study by the San Diego Association of Governments indicated that each 15-minute increase in vehicle wait time costs the local economy $1 billion in productivity and 134,000 jobs, annually. The region's stakeholders had made it clear to GSA that the port, which never shuts down, had to continue operating to preconstruction standards throughout the work.

That put the pressure on HP. "We agreed to not impact the wait times, which created a big problem for us," says Wellenstein.

In particular, disassembling the old administration building—constructed directly over I-5's 24 primary-lane inspection booths—and erecting in its place a 570-ft-long by 55-ft-wide canopy presented a "logistical nightmare," Wellenstein adds.

That became painfully clear on Sept. 14, 2011, when a suspended wood scaffold collapsed onto eight lanes of the inspection area. Seventeen people were injured, including travelers and construction workers, and 15 vehicles sustained damage. The accident interrupted port operations and construction for four days.

Fines issued to HP and its subcontractor AMG Demolition and Environmental Service by California's Division of Occupational Safety & Health (DOSH) were eventually dismissed. On Sept. 2, 2014, a DOSH appeals board reduced proposed penalties issued against a sub of AMG, Miller Environmental Inc., to $800 from $19,120. The biggest reduction was from $18,000 to $400 for alleged failure "to prevent dangerous accumulations of demolition debris on the scaffold."

"Cal OSHA has reversed its initial finding of overloading and all signals point to an inadequate scaffold design and installation that led to the collapse," claims Gregg Miller, president of Miller Environmental Inc., Orange, Calif. "There are multiple experts that have concluded that the scaffold design was inadequate and never met the design loads that it was advertised to support."

"Since we were closest to the issue we took the $400.00 general fine reduced from the $18,000 with no admission of guilt," Miller says.

Miller is in court with its scaffold subcontractor, Vertical Access Inc., Orange, Calif., over who pays for the mishap.

Michael D. Martinez, Vertical Access president and CEO, claims that his company is not to blame. "The overwhelming evidence shows that the scaffolding collapsed because of misuse by a subcontractor who overloaded the scaffolding with demolished debris. Vertical Access denies all liability," he says.

Soon after the incident, GSA announced that HP would be changing its demolition strategy: Travelers no longer would be passing under, and border protection staff would no longer be working beneath, suspended scaffolding. There have been no other mishaps.

The terrible site constraints even prompted GSA to put construction phasing in the design team's scope of services. "As an architect, we had never done drawings that took into account constructibility, [work] staging and phasing of an entire site," says Craig Curtis, a partner in the Miller Hull Partnership LLC, SYLPOE's master planner and architect.

The design team recommended modular elements, off-site assembly, laydown areas, demolition sequences, crane locations and even boom reach. "We were wearing the contractor's hat with no contractor on board," says Jay Taylor, principal-in-charge for the project's civil and structural engineer, Magnusson Klemencic Associates (MKA). "All the layers seemed overwhelming at first, but everything was so clear after we finished final concepts," he adds.

Throughout the work, site security kept everyone on their toes. Each of the 1,800 workers had to be vetted and badged. Six months into the job, CBP discovered that people were trying to slip across the border disguised as workers. After that, each day, workers were emailed a secret code from the CBP watch commander.

Document control also was sensitive. Any failed bidders had to return or destroy bid documents. For security, monthly aerial photos replaced a webcam.