The United States and Mexico this week opened their first new rail link in more than a century, connecting Brownsville, in Texas' Cameron County, with the neighboring city of Matamoros, Tamaulipas.

The West Rail Bypass International Bridge, which broke ground in December 2010 and is aimed at expanding the regional transportation capacity, will primarily be used by freight trains, according to the U.S. Department of Commerce. It is part of plans to update infrastructure used to carry nearly $600 billion a year in bilateral trade.

"The infrastructure has not improved" since the North American Free Trade Agreement went into effect more than 20 years ago, Secretary of Commerce Penny Pritzker told Reuters. In the meantime, trade between the United States and Mexico has increased six-fold, and the neighbor to the South has become one of the nation's biggest trading partners.

"We need to have infrastructure that lives up to the economic opportunities that are in front of both of our countries," Pritzker argued, noting that the West Rail project was part of that effort.

The bridge over the Rio Grande and the connecting tracks came at a price tag of more than $120 million and it replaces the 1910 rail connection that cut through a busy section of Brownsville and Matamoros that included school zones and frequently interrupted trade during peak business hours.

"In an increasingly globalized economy, our collective competitiveness depends on our ability to replace outdated infrastructure and continue to develop a modern, efficient, and secure border," said Sec. Pritzker during the ceremony. "That is why we are prioritizing the development and execution of border infrastructure projects like this one."

Over $1.5 billion worth of goods crosses the border between the two countries every day, 80 percent of which do it by rail, government numbers show. During the inaguaration ceremony, held in Brownsville, the secretary added that the Nogales-Mariposa port of entry update has been completed and the road entry point can now handle 4,000 trucks a day, up from 1,600.