Then out of nowhere, a flat ribbon of concrete runs like a roller coaster over giant pylons, burrowing in and out of the mountainside until it seems to leap midair over a 400-meter (1,200-foot) river gorge via the world’s highest cable-stayed bridge, called the Baluarte.

The Durango-Mazatlan Highway is one of Mexico’s greatest engineering feats, 115 bridges and 61 tunnels designed to bring people, cargo and legitimate commerce safely through a mountain range known until now for marijuana, opium poppies and an accident-prone road called the Devil’s Backbone.

Even those protesting the project say the 230-kilometer-long (140-mile) highway, expected to be completed in August, will change northern Mexico dramatically for the good. It will link port cities on the Gulf of Mexico and the Pacific by a mere 12-hour drive, and Mazatlan with San Antonio, Texas, in about the same time. The highway will eventually move 5 million vehicles a year, more than four times the number on the old road, plus more produce and goods from Asia to the Mexican interior and southern U.S.

Sinaloa state tourism officials predict an “explosion” for the resort city of Mazatlan, hard hit by drug violence in recent years, as the new road gives 40 million Mexicans in interior states an easy drive to the beach.

“It will change the landscape of this part of the country,” said Tourism Secretary Francisco Cordova. “It’s an opportunity to develop these areas and diversify the local economy.”

But it remains to be seen if the $2.2 billion highway will pull the towns of wood and corrugated-metal shacks in rural Sinaloa and Durango away from their historical ties to drug trafficking. In Concordia, the municipality that abuts the Baluarte Bridge in Sinaloa state, nine people were ambushed and killed last December as they ate their Christmas Eve dinner. The prosecutor blamed the attack on a war for control of drug trafficking.

The public security chief in Pueblo Nuevo, on the Durango side of the bridge, was gunned down a year ago by armed commandos as he walked down a street in daylight.

Government officials say the new road will bring legitimate economic activity to a troubled area. Locals say it may improve access, or take what little honest business they had as trucks and buses bypass towns altogether.

“It could leave some of the communities even more isolated,” said Jose Luis Coria Quinones, spokesman for 1,800 communal tree farmers, who have an injunction suspending construction on the Durango side near the bridge while a court considers their case. They say that the federal government hasn’t paid them sufficiently for access to their property during the construction and hasn’t repaired the damage caused to pine forests, water supplies and endangered species habitat.

From a distance, the Baluarte Bridge and its triangular web of steel cables are both spectacular and wildly out of place, a Golden Gate Bridge in the middle of a moonscape. While shorter than the Golden Gate, the Baluarte crosses a canyon deep enough to fit the Chrysler Building.

Engineers pump their fists when asked who designed it: “Puros Mexicanos.” All Mexicans.

A team of 60 to 80 experts started about 15 years ago in the Secretary of Communications and Transportation offices in Mexico City, said supervising architect Alberto Ortiz Martinez, using horseback, mule and helicopter to scope out possible routes. The entire road took 130,000 tons of steel and more than 20 times the concrete of an Olympic stadium.

Some 1,200 workers on the bridge lived for four years in a nearby encampment.

“The most complicated problem was getting there, to locations totally inaccessible, and bringing huge quantities of materials,” said engineer Jose Refugio Avila Muro, a federal subdirector of highway projects for Sinaloa state. He compared the topography to an electrocardiogram: “Lots of peaks, and you have to find a way to get to each peak from below. You just keep going, one by one, to each new point of construction.”

The new highway will cut the drive between Durango and Mazatlan to 2.5 hours from the current six hours of hairpin turns, few guard rails and the Devil’s Backbone, a stretch of road along the spine of a mountain with drops of hundreds of meters (feet) on either side.

Coming around a blind curve, a driver may suddenly have to negotiate passage between a semitrailer barreling downhill and a handful of cows tiptoeing along a narrow shoulder. Deadly accidents are common. A bus carrying mostly retiree tourists to Mazatlan plunged off the road a year ago, killing a dozen and injuring 22.

But the old highway is not the most forbidding part of the landscape.

From December 2006 until September 2011, when the federal government stopped providing numbers, Sinaloa and Durango on either side of the Baluarte Bridge were among the deadliest states in terms of drug-related killings. Mazatlan ranked 8th among Mexico’s more than 2,400 municipalities and Pueblo Nuevo, the municipality on the Durango side of the highway, was 35th most violent up to the end of 2010.

The U.S. State Department discourages travel in both states, except for specific tourist zones of Mazatlan.

The killings spiked in townships near the new road as a group known as the Mazatlecos and the Zetas battle for territory controlled by the Sinaloa Cartel, named for its home state and headed by Joaquin “El Chapo” Guzman, the world’s richest and most-wanted drug lord. A series of attacks around Concordia, Sinaloa, in late 2012, including the Christmas Eve massacre, caused some 250 families to flee their communities, said Concordia Mayor Eligio Medina. They have yet to move back.

Medina said the new highway could change the criminal dynamic, bringing tourism to colonial Concordia, founded in 1565 by the Spaniards as a way station between the coast and the gold mines. It’s also one of the most biologically diverse townships in the world, he said, noting that a new species of plant, the ageratina concordiana, was recently discovered there. He envisions everything from bird-watching to bungee jumping in Concordia’s Chara Pinta ecological preserve.

“The road will increase jobs and keep people busy,” Medina said. “When there is social mobility, criminal groups are more limited.”

Medina said the area is quiet again, with the Mexican military patrolling the towns that were attacked. Mazatlan tourism officials say killings there have dropped from 307 in 2011 to 43 so far this year. Latin America security expert Samuel Logan agrees the new road could be a boost to tourism and commerce, and but also to illegal transport.

“Maybe Concordia will grow and there will be a Holiday Inn Express there,” he said. “Will there be running daytime shootouts on this highway? Not likely. But will there be convoys of eight to 10 trucks going 90 mph (140 kph) filled with guys with guns? Probably.”