Two of fastest-growing cities in the U.S. lie less than 300 miles apart in the American southwest. Las Vegas and Phoenix, ranked third and seventh respectively in population growth from 2000 to 2012, also happen to be two of the biggest U.S. cities not linked by an interstate highway.

There are those who would like to change that. In fact, Nevada and Arizona recently wrapped up a two-year study that examined the possibility of building Interstate-11 from the U.S.-Mexico border in Arizona to the U.S.-Canada border.

“It’s necessary to continue to look at this,” said Sondra Rosenberg, I-11 project manager for the Nevada Department of Transportation. “There’s absolutely justified investment in further study.”

Lance Jungmeyer, president of the Fresh Produce Association of the Americas, Nogales, Ariz., said I-11 could do for transportation in the western United States what I-35 has done for in the middle of North America — create an international trade corridor.

Although the overall goal is broad, linking three countries, Rosenberg said the states are viewing the project in smaller segments. Linking Phoenix and Las Vegas is one of the top priorities, but Nogales to Phoenix also is a focal point.

“It would be a way to get produce from Nogales to Las Vegas a lot quicker,” Jungmeyer said. “Las Vegas is a huge food destination.”

Having a north-south interstate also would expedite shipments that now must often travel to Los Angeles and through congested California highways to make their way north.

“It’s not a good way to move produce,” Jungmeyer said.

Fixing the problem, he said, could take decades.

Rosenberg said there are constraints that must be overcome, including environmental concerns and land ownership issues. She said that makes it likely that building I-11 would involve upgrading existing roads to interstate standards rather than designing and implementing new totally new construction, which would require even more significant resources and involve more property complications.

That means the creation of I-11 likely would involve upgrading U.S. 93 between Phoenix and Las Vegas and U.S. 95 from Vegas to Reno.

“U.S. 93 is not true freeway,” Rosenberg said. “As you go through small towns, there are still stoplights and stop signs.”

U.S. 93 used to be a two-lane road with passing lanes, but the highway has been gradually improved and expanded in Arizona, and there are plans to make it a four-lane divided highway. The road still has access control issues, she said.

U.S. 95 remains is an undivided, two-lane highway in some portions of Nevada.

Jungmeyer said states need a long-term commitment from Congress in order to make significant investments in major projects. Instead, the Highway Trust Fund was on the verge of insolvency in August before legislators passed a $10.9 billion, nine-month extension. The trust is funded by an 18.4-cents-per-gallon federal gas tax, which hasn’t been increased in more than 20 years.

“We don’t have a long-term bill,” Rosenberg said. “I-11 is a big investment over the long term. It’s difficult to determine a schedule. We’re looking at segments to see what we can get done, what immediate steps that can be taken.”

Rosenberg said the first stretch of I-11, a bypass around Boulder City, Nev., has funding and is expected to be completed in 2018.

“Beyond that, it depends on funding allocation,” she said.

Construction of the nation’s interstate highway system began in 1956 and was completed in 1992. Thus, some southwestern cities weren’t deemed priorities at the time.

“Both cities were a fraction of what they are today,” Rosenberg said of Vegas and Phoenix. “These cities boomed in the last couple of decades.”

Las Vegas’ population grew more than 40% from 2000 to 2012, while Phoenix grew 32% during the same time.

“There’s a big push to expand manufacturing in Nevada and diversify state economies,” Rosenberg said. “If we do that, a more robust transportation system is needed.”