Most of the drug shipments smuggled into the United States by the Mexican cartels are hidden in trucks that drive across U.S. border checkpoints in plain sight, with little fear of inspection, U.S. law enforcement officials tell ABC News.
Only about 5 percent of trucks coming into the country from Mexico are inspected, according to U.S. officials.
Watch "World News with Charles Gibson" tonight at 6:30pm ET and "Nightline" at 11:30pm ET for Brian Ross' full report.
"It is just too costly and too slow given the volume of trucks to actually try to stop and inspect each and every truck," said Juan Zarate who dealt with the issue in the Geroge W. Bush White House as Deputy National Security Director.
The number of trucks coming into the U.S. has steadily increased since the passage of NAFTA in 1993. Almost 3,000,000 loaded container trailers crossed at border checkpoints last year.
"It does open up the potential for drug networks to take advantage, but I think it is something we have to find alternative ways of addressing," said Zarate.
Any attempt to inspect all trucks crossing the border, "would have a hugely negative impact in terms of commercial traffic and trade between the United States and Mexico," said Zarate, who also held the position of Deputy National Security Advisor for Combating Terrorism.
"You would see lines like you wouldn't believe," he said.
The Mexican cartels' fleet of 18-wheelers has long since replaced the Caribbean air drops and speed boats used by the Colombian cartels in the 1980's and 1990's, the era of "Miami Vice".
And major cities at interstate highway junctions, like Atlanta, have become important hubs for the Mexican cartels.
"Atlanta is a central trans-shipment point for pushing narcotics to some of the largest distribution cells in the United States," said Rodney Benson, the Special Agent in Charge of the DEA office in Atlanta.
Instead of tracking fancy sports cars at glitzy night clubs in Miami, federal drug agents now spend a lot of their time trailing behind huge 18-wheel trucks and conducting surveillance at interstate truck stops.
Flying over Atlanta's "Spaghetti Junction," the intersection of interstates I-85 and I-285, Benson pointed out the truck stops and warehouses where his agents have made major arrests and drugs seizures.
"It's also a major money collection point," said Benson. "They do operate with a business-like efficiency," he said.
Federal agents and local police say the Mexican cartels often rent homes in quiet, upscale suburban neighborhoods for their operatives.
"You couldn't build a better environment to camouflage this activity," said Gwinnett County district attorney Danny Porter.
In a major raid last week, aimed at the Atlanta operations of Mexico's Gulf Cartel, police and federal agents raided 16 locations and arrested 21 people.
Nearby residents were shocked to learn their neighbors might be connected to the Mexican cartels.
"Their daughter goes to school with my daughter," said Amber Youngblood of Duluth, Georgia. "It makes you think twice about who your neighbors are," she said.